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Where are your tree’s roots? Are they deep-rooted or shallow-rooted? What difference does it make?
A single tree can have hundreds of miles of roots, and hundreds of thousands of root tips. Approximately 20% of a tree’s weight is found in the root system. That means an 80’ hardwood tree, with a 24 inch diameter, which weighs approximately 10 tons, can have 4,000 lbs. of roots. [Your average new car weighs 2,871 lbs.] That’s a lot of roots. Function of tree roots Tree roots serve several functions. They anchor the tree in place. Tree roots absorb and store water, oxygen, and nutrients from the soil, compete with neighboring plants, and maintain incredible relationships with beneficial fungi and bacteria found in the soil. You may not think of tree roots when it comes to photosynthesis, but you should. According to Thomas O. Perry, in a report published by the Harvard Arboretum, tree roots produce produce nitrogenous compounds that are essential to photosynthesis. Knowing what your trees’ roots are doing, and what they need, can help you keep your trees healthy and productive. But it all starts with the first root. The first root The first root that emerges from a tree seed, be it an acorn, peach pit, or pine nut, is called the radicle. The radicle nearly always grows straight down, pulled by gravity. Once the radicle is established in a place where it can absorb water, oxygen, and nutrients, further root development continues.  I. Seed. II. Water uptake ruptures seed coat. III-V. Radicle (1), plumule ( 2), and the cotyledons (3) unfold. VI. Fibrous root system begins to emerge (Noahjgagne) CC BY-SA 4.0 Taproots and oxygen In some cases, such as walnuts, pines, and oaks, the taproot persists, growing down 3 to 6 feet. This taproot can grow extremely deep, under ideal conditions, but that's rare. Other trees develop a system of fibrous roots, and the taproot is not maintained. Tree roots move through the macropores and micropores found in the soil. If the soil is too hard or compacted, roots cannot move through it. Tree root growth generally stops when insufficient oxygen levels are encountered. This can be caused by compaction, the presence of hardpan, or by flooding. Cherry trees are particularly sensitive to insufficient oxygen in the soil, which is why they tend to be difficult to grow in compaction-prone clay. [Their roots contain chemicals that turn into cyanide gas when oxygen levels are too low! (Rowe and Catlin, 1971)] Perennial roots The place where major roots emerge from the subterranean trunk is called the root collar. Most trees put out 4 to 11 major roots that grow horizontally from the root collar. These roots are generally found in the top 12 inches of soil, though they can range 3 to 7 feet deep, depending on age, species, and local conditions. These roots are can be 3 to 15 feet long, and up to 1 inch in diameter. Like trunks and branches, these woody, perennial roots develop growth rings, and they provide anchoring support from which all the transport roots emerge. Transport roots Transport roots normally fill a circular area that can be 4 to 7 times greater than the drip line. Transport roots do exactly what their name implies: they transport resources collected by the root hairs into the vascular bundles that feed the rest of the tree. To take good care of your trees, you really need to know where these roots might be. GARDEN CHALLENGE: Where are your roots? I challenge you to learn where your trees’ roots right be. You can do this outside, with a tape measure and a long rope, or you can do it on your computer, or with paper and pencil. However you do it, it will probably surprise you just how far these roots go. Regardless of the method you use, these steps will help you learn where your trees’ root might be:
Note how the root systems of all your trees (and large shrubs and everything else) overlap in significant ways. Also note where those root systems might end up covered by your house, the street, or some other dead zone. [Printouts of current satellite views of your property are very handy for activities like this one.] But there is a lot more to tree roots than perennial and transport roots. There are some roots you’ve never seen, and some you’ve probably never even heard of!
Striker roots In particularly dry, sandy soil, trees will put out striker roots. Striker roots grow straight down, from the perennial roots, until they encounter a barrier or insufficient oxygen. These striker roots, as well as taproots, then start branching out horizontally, creating an entirely new layer of root system. Feeder roots Feeder roots are where all the action happens. These are the microscopic root hairs (which aren’t actually hairs at all) that interact with water, oxygen, and mineral molecules found in the soil, along with billions of soil microorganisms that make everything possible. These feeder roots grow upward into the top soil to collect (and disperse) nutrients, oxygen, and water. Causes of tree root damage You may be surprised to learn that fully 99% of a tree’s roots are found in the top 3 feet of soil, and that it is a lot easier than you might expect to damage those roots. Tree roots are frequently damaged by drought, flooding, extreme temperatures, the presence of rocks or hardpan, nematodes, springtails, and root-eating vermin, such as voles. Tree roots can also be damaged by human actions, even when our intentions are good. These actions include:
Signs of root damage Tree roots can be seen as a reflection of the aboveground portion of the tree. Not necessarily in terms of size or shape, but in overall health. For example, if the leaves are repeatedly removed from a tree, some of the roots will die, as well. In the same way, if a portion of the root system is damaged or drowned, a corresponding dieback of the aboveground portion of the tree can be seen. The vascular systems of some trees, such as oaks, are tied directly to branches on the same side of the tree. Damage to the roots will be reflected in poor health or death of branches on the same side of the tree. In other cases, portions of roots are tied to branches on the opposite side of the tree, while others have more of a spiral or zig-zag vascular system that serves the entire tree. These patterns can vary between species and individual trees, but arborists use this information to sort out problems related to irrigation, pesticides, fertilizers, insecticides, and herbicides. Helping tree roots You can help your trees’ roots stay healthy by aerating the soil, avoiding compaction, irrigating properly, mulching, and top dressing with organic material. These actions will help the worms, microorganisms, and other processes “fluff” the soil, improving soil structure, and provide important nutrients. Unlike the crown shyness seen above ground, where the leaves of individual trees avoid touching, the root systems of different trees, shrubs, and other plants can intertwine in complex networks that are made evermore astounding when you learn how they use soil microorganisms to share nutrients and to communicate. [We’ll talk more about that later.] In situations where several of the same species of tree are growing near each other, the roots of one tree will graft to the roots of another tree. [I’ve said it before, I’ll say it again - the more I learn, the weirder the world gets!] I hope that you can now see your trees with new eyes, eyes that can better imagine what is happening underground and under your feet. Fragrant pine needles are modified leaves. Unlike the soft, flat leaves of broadleaved plants, many evergreens have evolved an entirely different sort of leaf, the needle. #/media/File:Pinus_albicaulis_pollen_cones-crop1.jpg) Five-needled fascicles on a twig of 'Pinus flexilis' (Public Domain) Most plants with needles need very little water, which means they are called xerophytes. These plants also tend to grow at higher elevations. Each tree produces millions of needles over the course of its life. The physiological characteristics of needles are an adaptation that allow evergreens to thrive where other plants would perish. Benefits of needles Conifer needles have many characteristics that allow them to hang on to the water absorbed by the roots:
The dark green color of most needles also aids in collecting the sun’s energy. Anatomy of a needle Even though needles look very different from classical leaves, they still have many of the same structures and functions. For example, needles perform photosynthesis. The stomata, used in gas exchanges and moisture level control, are arranged in lines, down the length of the needle, or in small patches.  Cross section of pine needle (Lord of Konrad) Public Domain Needles often grow in clusters, called fascicles. There are also single needle fascicles. The number of needles found in a single facile can help you identify the species. At the base of needles, you will see a sheath, called the fascicle sheath. This sheath can be persistent, as in hard pines, or deciduous, as with soft pines. #/media/File:Pinus_monophylla_foliage-crop1.jpg) Single-needled fascicles on a twig of Pinus monophylla (Clinton Steeds) CC BY 2.0 Most needle-bearing trees are evergreen, though there are a few deciduous species. Just as the leaves of deciduous trees change colors and fall in autumn, the needles of many evergreens also change color and fall, it’s just not as obvious. This is a natural occurrence, much like citrus June drop. Most evergreens hold onto their needles for 2 or 3 years. Discarded needles are usually those found closer to the trunk. If needles are lost elsewhere on the tree, or if needles are discolored, it can indicate fungal disease. Needle pests and diseases Pine wilt can also cause discolored needles. Pine wilt is caused by pinewood nematodes, which attack the vascular tissue. Pinewood nematodes move from tree to tree by catching a ride on pine sawyer beetles, in a behavior called phoresy. Pine needles are a favorite food of some moth and butterfly species, as well as the pine sawfly. Goats will eat pine needles, too, but you wouldn’t want to drink the milk they produce after that snack. It’s nasty. Acidic pine needles There is a popular misconception that pine needles can be used to acidify soil. While it is true that fresh pine needles are slightly acidic, and a thick layer of needles on the ground can interfere with the growth of competing hardwoods, the dried needles, often called pine straw, are not acidic. While they will improve soil structure by adding organic material as they decompose, pine needles will not, I’m sorry to say, acidify your soil. Pine needles can be steeped in boiling water for a refreshing tea that is high in vitamins A and C. Pine needles have long been used to make baskets, trays, and other crafts. Here is a pine needle basket made by my grandmother.  Pine needle basket If extrafloral nectaries are not super-sized nectarine flowers, what are they? While most plants produce nectar in their flowers to attract pollinators, there are over 2,000 plants that produce nectar in other places, and for entirely different reasons.  Extrafloral nectaries on passionflower petiole (Eiku) CC BY-SA 4.0 What are extrafloral nectaries? Nectar is the currency used by plants to attract beneficial insects. Nectar is manufactured in glands, called nectaries. Nectaries are usually found in flowers. When these glands occur elsewhere, usually on leaves or stems, they are called extrafloral. So, extrafloral nectaries (EFN)s) are knob-shaped, nectar-producing glands found on leaves and stems. These glands can take many different forms. Some are very primitive in structure, while others are highly complex. Regardless of the form, the nectar produced by EFNs is surprisingly consistent across species, and around the globe. This is in direct contrast to the wide ranging differences found in the nectar produced by flowers. Why do plants have extrafloral nectaries? If nectar is supposed to attract pollinators, why would it occur on stems and leaves? The most popular theory asserts that extrafloral nectar attracts insects, spiders, and crustaceans that protect the plant from sap-sucking, plant nibbling, seed eating pests. There is another theory that claims extrafloral nectaries may also serve a waste elimination function, but that theory is not nearly as popular, or as appetizing. Many beneficial insects (and some not so beneficial insects) are attracted to EFNs, regardless of the reason.  Ant visiting extrafloral nectary of Senna stem (Beatriz Moisset) CC BY-SA 4.0 Insects attracted by extrafloral nectaries Scientists believe this structure evolved on vining plants, due to ant traffic. Ants are one of the most frequent visitors to extrafloral nectaries. Since ants frequently carry diseases from one plant to another, and they farm aphids, I don’t usually count them as beneficial insects, even though they do help aerate the soil. Recent research, however, has also shown that ants serve a valuable function to trees by feeding on nectar and harmful insects, and then pooping those nutrients onto leaves. Those nutrients are then absorbed through the leaf, providing valuable plant food, right where it is needed. A few, full-blown pests, such as Florida’s lovebugs, also tap into this food resource. For the most part, it is beneficial insects, such as ladybugs, lacewings, praying mantids, and wasps, who are attracted to extrafloral nectaries. Some plants provide sheltered chambers, called domatia, for similar benefits.  Extrafloral nectaries on sweet cherry petiole (André Abrahami) CC BY-SA 2.5 Plants that feature extrafloral nectaries
There are over 2,000 plants that have extrafloral nectaries. All cucurbits and many members of the Prunus and legume families feature extrafloral nectaries. This means that your squash, melons and gourds have these knobby glands, as do your peach, apricot, nectarine, cherry, and plum trees. Cowpeas and elderberries do, too. Common vetch, willow, peonies, and many ferns, vines, and carnivorous plants also feature extrafloral nectaries. [Some scientists disagree with ferns being included in this list, since ferns do not produce flowers. Those scientists call these glands ‘extrasoral’.] As more botanical research is conducted, we are learning than the food provided through extrafloral nectaries is critical to biodiversity, especially during times of drought. Which plants in your garden have extrafloral nectaries? Flowers come in many shapes and sizes. When a flower cluster has a flat or dome-shaped profile, it is said to be corymb [kor-im].  Carrot umbel (Alvesgaspar) CC BY-SA 3.0 Corymb comes to us from the Greek word (korumbos) for ‘cluster’. The only reason this information is important, besides helping you win more often in word games, is that it can help you to identify plants of mysterious parentage. So, let’s find out more about corymbs and flower clusters. [And don’t let all the new words scare you off.] Umbels and corymbs First, we need to differentiate between umbels and corymbs. Umbels are flower clusters that look like umbrellas. The tiny stems, called pedicels, all emerge from a central stalk. Carrot, dill, and parsley flowers are all umbels. If a flower cluster has many branches, instead of a single point of contact, it is called a panicle. [But don’t panic! You can do this!] Flower clusters Flower stems are called peduncles. As soon as the tiny stems of a flower cluster begin to emerge, that main stem changes its name to rachis [ray-kiss]. Each individual stalk within a flower cluster is called the pedicel. Each pedicel holds a floret. Pedicels can be arranged in pairs (parallel), or they can take turns (alternate).
Types of corymbs Corymbs may be flat-topped or convex. This is because the tiny stems, or pedicles, get progressively longer as they move away from the center. If the pedicels of a corymb all emerge from the central rachis, it is said to be racemose. If there are several layers of branching rachis, it is called cymose.
Cymose corymbs
Cymose corymbs are said to be determinate. Determinate inflorescences have a flower on the top that halts further growth. This top (apical) flower is the oldest one in the bunch. Younger flowers develop below this primary flower. Forget-me-nots, jasmine, and figs are all cymose. Racemose corymbs Racemose corymbs, or racemes, are said to be indeterminate. Indeterminate inflorescences are those with the oldest florets at the base and newer growth at the top. They just keep on growing. Cherries and other stone fruits all have racemose corymbs. Snapdragons and yerba maté are also racemes. The next time you look at a flower cluster, take a moment to see if it is built like an umbrella (umbel), if its branches are all connected to a central stem (raceme), or if there is a complex system of branches (cymose). This can help you make better use of the many plant identification tools available online. Accessory fruits are not designer handbags or the latest fad. In the word of botany, accessory fruits are more familiar that you might expect.  Strawberries are accessory fruits (Alexas_Fotos) Pixabay What is fruit? Fruit is the tissue that surrounds the seeds of angiosperms (flowering plants). Fruit tissue is made from the ovary. Except when it isn’t. In some cases, a fruit develops from both the ovary and nearby tissue, found outside of the carpel. These neighborly tissues can be either the perianth, the flower whorls, or the hypanthium, the flower base. When this occurs, the part we eat is called an accessory fruit.  Parts of a flower (LadyofHats) Public Domain Popular accessory fruits
Using our botanical definition of an accessory fruit, we learn that pineapples are accessory fruits because the fruit is made from the ovary plus tissue from the pistils and sepals. We also learn that strawberries are accessory fruits. [The seeds you see on a strawberry fruit are actually achenes, a type of dried fruit. Each achene develops from a single pistil.] Other popular accessory fruits include apples, figs, mulberries, and pears. And those delicious cashew nuts? Those are the seeds of the cashew apple, another accessory fruit. Now you know. The truth about nuts may surprise you. While you probably already know that peanuts are not nuts (they’re legumes), many of the other foods you have come to know as nuts are not true nuts at all. Let’s begin by learning the botanical definition of nuts.  Raw mixed nuts (Kai Reschke) Pixabay True nuts are hard-shelled, inedible pods that hold both the fruit and the seed of a plant. These pods do not open of their own accord, which means they are indehiscent. The pod, or shell, of a nut is made from the ovary wall, which hardens over time. Hazelnuts, chestnuts, and acorns are true nuts. So are kola nuts, which gives “cola” soft drinks their signature flavor.  Immature hazelnuts (Thomas Molnar, Rutgers University, Dept. of Plant Biology and Pathology) CC BY-SA 2.0 [Did you know that small nuts are called ‘nutlets”? To me, that sounds like the perfect name for a little chihuahua.] So, when is a nut not a nut? A nut is not a nut when it is a fruit seed. Fruit seeds can be angiosperm, drupe, or gymnosperm seeds:
These not-nut nuts are commonly referred to as culinary nuts. [Did you know that cashews are the seeds of an accessory fruit, which means they share characteristics with strawberries and poison ivy. Isn’t botany amazing?]  Ripe cashew apples with seeds hanging below (Abhishek Jacob) CC BY-SA 3.0 Of course, you can call any of these delicious morsels "nuts" whenever you want to. True nut or culinary nut, many of these yummy snacks find their way into our gardens and foodscapes. Which ones are you growing?
Plant prickles are skin spikes. Unlike thorns, which are modified shoots, and spines, made from modified leaves, prickles are spiked skin extensions. .jpg) Silk floss tree truck (Rhododendrites) CC BY-SA 4.0 Because prickles are made out of epidermis and cortex tissue, they can occur anywhere on a plant. This is also what differentiates them from the hairs (trichomes) growing on your squash plant leaves. Trichomes only contain epidermis tissue, whereas prickles contain both epidermis and cortex. #/media/File:Stem-histology-cross-section-tag.svg) Cross section of flax stem: 1. Pith 2. Protoxylem 3. Xylem 4. Phloem 5. Sclerenchyma 6. Cortex 7. Epidermis (SuperManu) Public Domain The purpose of prickles The most obvious purpose of prickles is to make plants less palatable to herbivores. Chewing on a stem covered with prickles can’t be very appealing. In extreme cases, such as the silk floss tree, the entire trunk is covered with massive prickles. I suppose that’s the level of protection needed in rural South America. While prickles are generally meant to keep herbivores away, most species specific pollinators have learned to maneuver around the prickles without too much trouble. Prickles can also provide limited amounts of shade or insulation from temperature extremes. A rose by any other pokey bit Everyone calls the sharp bits on rose stems thorns, but they are actually prickles. One easy way to tell if a protuberance is a prickle, thorn, or spine, is by how easy it is to remove. Spines and thorns contain vascular bundles, but prickles do not.  (A) Thorn or spine (B) prickle (CASF) CC BY 3.0 This is why it is so easy to flick a rose thorn from its stem, while trying the same trick on your orange tree won’t work. Orange tree thorns have added strength from the phloem and xylem, carrying water and nutrients into the pointy protuberance. Thorns do not have that type of attachment, so they are easier to remove.
So, now you know the difference between thorns and prickles. A person is called pithy when they are concise and forcefully expressive. Did you know that many plants can also by pithy?  Elder shoot cut to show white pith in the center, surrounded by yellow wood (MPF) CC BY-SA 3.0 Pith, also known as medulla, is a type of plant tissue that stores and transports nutrients. Typically, it is very soft and spongy. Stem pith In the very center of many stems, you can see a spongy area. This is particularly noticeable inside sunflower stems and their central cores, or steles. This is pith. Xylem surrounds the pith, and phloem are outside of the xylem. When pith first develops, it is white. As it ages, it can darken. In some plants, the pith may disintegrate completely, while, in others, the pith may have a chambered structure.  Chambered pith of walnut stem (MPF) CC BY-SA 3.0
Hesperidium is the name given to certain types of fruits. Hesperidia are berries with a tough, leathery skin that tends to be bitter.  Hesperidium ‘C. australasica’ (Ivar the Boneful) CC BY-SA 4.0 If you cut a hesperidium open, you will see separate compartments, called carpels. Within these carpels, you will see hundreds of tiny, fluid-filled vessels that are made out of specialized hair cells. These vessels are called vesicles.  Common hesperidium (USDA) Public Domain If you haven’t already guessed, all citrus fruits are that special type of berry, known as hesperidia.
Bud scar may sound like a great punk band name, but knowing how to recognize this tiny bit of plant anatomy can come in handy. At the tip of most twigs is an area of meristem tissue. This plant tissue can turn into several different types of plant cells. When the tissue grows upward, to continue the trunk of a tree, or a branch stem, it is called apical meristem, or a terminal bud. In this sense, terminal does not mean lying on its death bed. Rather, it refers to the bud at the end of the branch. As these terminal buds burst forth with new growth, the protective scale normally falls away, leaving a bud scar. Bud scars look like rings around stems and branches of trees and other woody plants. Bud scars are from the terminal bud on a stem. These marks are different from leaf scars. Leaf scars occur at the point of attachment for a leaf, after the leaf has fallen off. Just above a leaf scar, there is usually a lateral bud that can grow into a twig or flower.  Almond bud scar Ultimately, the growth of the tree or branch will grow over these scars, but that can take a long time. Until then, you can use the number of bud scars to determine the age of a branch, since each terminal bud indicates one year’s growth.
As a child, I would eat around the center core of my carrots, leaving the darker, sweeter core for last. I didn’t know it then, but that inner core is called the stele.  Carrot steles are far more visible in purple carrots (Kate Russell) Vascular plants have both root and stem steles, but they didn't start out that way. Primitive steles were nothing more than a strand of xylem, surrounded by phloem. [Remember, water and minerals ‘rise up the xylem’ from the roots, and manufactures sugars ‘flow down the phloem’ from the leaves. In case you forgot.] More modern steles may consist of vascular tissue, pith, and pericycle. Pith is the spongy material seen in the center of stems, and the pericycle is a thin layer of tissue between the xylem and the endodermis. There are two major types of stele: protostele and siphonostele. #/media/File:Protostele.jpg) Types of protostele (EncycloPetey) Public Domain Protostele Protostele describes the more primitive stele, which consists of a strand of xylem, surrounded by phloem. Protosteles may or may not have an endodermis that controls the flow of water. There are three different types of protostele:
Siphonostele Siphonosteles are a little more complex than protosteles. Siphonosteles may have gaps in their vascular tissue in places where leaves are born. These spaces are called leaf gaps. You can think of these leaf gaps as sections cut from a hula hoop and pulled a little apart, making room for leaf tissue to grow through. Siphonosteles also contain pith. If the xylem is found only outside of the pith, it is called ectophloic. If the xylem can be found both within and outside of the pith, it is called amphiphloic. Members of the nightshade family, such as tomatoes and peppers, are amphiphloic. There are three types of amphiphloic steles:
#/media/File:Siphonostele.jpg) Types of siphonostele (EncycloPetey) Public Domain Stele diseases
Diseases of the stele include phytophthora root rot, verticillium wilt, black root rot, and crown rot. In each case, prolonged exposure to wet soil creates the conditions needed for pathogens to infect your plants. Maintaining good drainage and soil structure can help prevent these diseases. So, why would you care what sort of stele your plants have? Besides sounding really smart, being able to look up information about what’s inside a plant stem can help you identify unknown plants. What's inside your stems? Every rose has its thorns, right? Well, no. They don’t. Roses do not have thorns. Roses have prickles. Citrus trees have thorns.  Lemon tree thorns Thorns, prickles, and other spiky bits
Thorns are a type of spinose structure made out of a modified leaf, stem, root, or bud. Many people use the terms bristles, prickles, spines, and thorns interchangeably. Botanically, these terms mean very different things:
So, where bristles are stiff hairs and prickles are hard, spiked skin (neither of which contain plant veins), spines, being modified leaves, and thorns, modified stems, do contain plant veins. Thorny problems Plants use thorns as a mechanical defense against herbivores (and gardeners). Cacti are far less likely to be eaten when they are covered with hard thorns. And the pollinators who specialize in pollinating these particular types of plants seem to be unaffected by the presence of thorns. In some cases, thorns are also used to shade certain plant varieties, or to provide a layer of insulation. Home, sweet thorn Some thorns are hollow. These tiny chambers are called domatia. Plants, such as certain acacia species, produce domatium to provide shelter for beneficial arthropods (insects, spiders, and crustaceans). Similar to galls, which are produced by the resident, rather than the landlord, domatium are the plant’s side of a mutually beneficial relationship, most commonly with ants or mites. Occasionally, thrips may also move into these tiny apartments, but they are generally unhelpful to the plant. The plants that create these thorny thresholds are called myrmecophytes. While I do not expect any of you to stop calling rose prickles thorns, why not impress your friends with your new-found knowledge? Wax is made by honey bees to build the comb used to store honey and to protect larvae. Did you know that plants also make wax?  Water beads on the waxy cuticle of a kale leaf (Rei) CC BY-SA 3.0 Nearly all vascular plants manufacture wax. This wax is used as part of the cuticle, or outer layer of the epidermis, of leaves, stems, and even some fruits. Protective wax Having a waxy outer layer reduces evaporation, making it easier for plants to hang on to the water they need. It also reduces the chance of abrasion, when plant parts rub against each other. Finally, wax makes it more difficult for pests to attack. Wax chemistry Wax is actually a class of fatty compounds that are insoluble in water and tend to be relatively soft at room temperature. When honey bees are between 12 and 20 days old, they develop a special gland on their belly that converts the sugars in honey into waxy flakes. The flakes are collected by other bees and chewed up before being used to make new comb. [I thought you’d want to know about that.] Plants, however, have neither the organ nor the chewing ability. Instead, plants synthesize wax out of hydrocarbons, made up of fatty acids and long chain alcohols, along with aromatics, ketones, and other chemicals. The chemical make up of a plant’s wax varies by species and geographic location.
Plant wax candles Carnauba wax, of shiny car and confectionary fame, is a wax made by the Brazilian palm Copernicia prunifera. A lighter colored substitute, ouricury wax, comes from the Brazilian feather palm Syagrus coronata. Several species of native bayberry (Myrica cerifera), also known as wax myrtle, and the succulent stems of candelilla (Euphorbia antisyphilitica), produce so much wax that they were used by Native Americans to make candles. In the case of bayberry, the berries are boiled until the wax separates from the plant material. After it hardens, it is removed from the soup. These candles are still made today, due to the pleasant smell as they burn. Candelilla plants are now endangered and collecting them is forbidden. Other plant waxes include castor wax, rice bran wax, and tallow tree wax.  Bayberry candles The next time you look at a leaf or stem, take a closer look and see if wax is part of that plant’s defense system.
What bottle of wine would be complete without its cork? The same is true of most trees. Everyone knows that trees and woody shrubs are made of wood, surrounded by bark. But there’s a lot more going on in those outer layers than meets the eye. #/media/File:1-Arraiolos-0050.jpg) Cork oak (Sallyofmayflower) CC BY 3.0 The bark you see protecting the living wood of a tree is made up of dead plant cells. This layer is called the rhytidome. The reason these cells are dead is because the cork layer cuts them off from the tree’s resources. Components of bark Bark is made up of three basic layers. The inner layer, or phloem, is a living part of a tree’s vascular system. Manufactured sugars ‘flow’ down the phloem to feed the rest of the plant. The middle tissue, or cortex, is made up of porous tissue that stores and transports carbohydrates, tannins, resins, and latex. The outermost layer of bark is called its periderm. #/media/File:Tree_secondary_components_diagram.png) Tree cross section diagram (Brer Lappin) Public Domain Periderm
The periderm is also made up of three layers: the cork, cork cambium, and phelloderm. Cork (phellem) is produced by a specialized layer of cambium tissue, known as the cork cambium, or phellogen. This cork cambium layer is only one cell thick and the cells divide in parallel (or periclinally) toward the outside of the tree. In some trees, the cork cambium layer also produces cells towards the inside of the tree. These inner cells are the phelloderm layer. Function of cork Cork keeps wine safe from the elements because it is impermeable to gases and water. Because of the cork, your wine stays where it is and (as long as the cork remains intact) will only grow better with time. The cork of a tree also blocks air and water. Cork is able to keep trees and wine safe from the elements, along with insects, bacteria, and fungal disease because it contains suberin. Surberin is a waxy material that creates a protective barrier. This barrier also blocks water and gas exchanges between the outermost layers of the tree killing the epidermis, cortex, and secondary phloem. This is the bark you see. Trees and shrubs also use cork to cut off an unwanted body part (leaf, diseased twigs, mature fruit) from the rest of the plant. This is called abscission. If you pick a dandelion, you will see a viscous, milky white goo come out of the stem. That goo is latex. Exposed to the air, latex coagulates, creating a protective barrier. Plants use latex as a defense against insect feeding. [Slugs will eat leaves drained of latex, but not before.] We use latex in very different ways.  Dandelion with stem exuding latex Latex gloves, latex paint, and cosmetic sponges all get their start from latex. So do chewing gum, balloons, adhesives, and opium. The latex collected from the rubber tree is where we get, you guessed it, rubber. [Most latex paint, such as is used in whitewashing, is actually a synthetic latex.] It is estimated that 10% of all flowering plants, angiosperms, contain latex.
Plants that produce latex
There are over 20,000 species of plant that produce latex, occurring in over 40 plant families. Some of the more commonly known latex-producing families include:
Some mushroom, conifer, and fern species also produce latex as a defense mechanism. Allergic reactions to latex Because latex contains defensive chemicals, it can be an irritant. Prolonged exposure can lead to an allergic response. Individuals with a latex allergy are at risk for anaphylactic shock and should avoid contact. Some forms of latex can cause blistering of the skin, or blindness, while other plants produce a latex with reduced amounts of the allergen. As you work in the garden, note which plants exude latex when damaged. And monitor your skin for reactions to this liquid plant defense. When you look at a flower, you probably notice the petals first. Bright colors and brilliant arrangements attract people and pollinators alike. All of those petals together are called the flower’s corolla, or inner perianth. At the base of that corolla, you will sometimes see a green cup shape made up of lobes. The lobes together are called the calyx, or outer perianth. Each lobe, individually, is called a sepal.  Green sepals of an oyster plant flower Supportive sepals Sepals encase a bud before the flower blooms, providing protection. Usually, after the flower blooms, the plant has no use for the sepal and it is allowed to whither. Some flowers retain their sepals, using the cup-like structure for added support for the flower. In some cases, such as oyster plants, the sepals are quite large and they protect the nyctinastic flower during the afternoon and through the night. Tomatillos and groundcherries, however, put their sepals to work as papery outer coverings for their precious fruit. These protective bladders help keep birds and insect pests away.  Tomato sepals are the spikes sticking out just above the fruit Sepal description
Like flower petals, sepals are modified leaves. While often smaller than the petals, sepals can be longer and larger. Sepals can look like teeth, ridges, or scales, especially on plants in the grain family, or they can look like leaves or petals. Normally green, they can also be very colorful and may look like petals. When the petals and sepals are too difficult to tell apart, they are called tepals. Flowers with tepals are called petaloid. Tulips and aloe plants are petaloid. Sepal attachment Some sepals are attached or fused to each other (gamosepalous), while others are separate from one another (ploysepalous). When the sepals are fused toward the base, as in the case of legumes and pomegranates, they form a calyx tube. In the rose and myrtle plant families, this structure is called the hypanthium. Sepal count and plant classification The number of sepals present can help with plant identification. The number of sepals is called its merosity. Eudicots generally have a merosity of four or five, while monocots and palaeodicots have a merosity of three. If you see a flower with 4 or 8 sepals, you will know that it is a eudicot. If it has 3, 6, or 9 sepals, it is either a monocot or a palaeodicot. If is has 15 sepals, well, you’re on your own. Achenes are small, one-seeded dry fruits that do not open to release the seed, which means they are indehiscent. [Pronounced ah-KEEN or eh-KEEN, depending on who you ask.] Examples of achenes The tiny bits that you see on the outside of a strawberry are achenes. If you look closely, you will see that each tiny bit is actually a dried fruit that contains a single seed. If those seeds happen to sprout while still attach to the strawberry, it is called vivipary.  Strawberry achenes (Rich Caulton) CC BY 4.0 Many members of the sunflower family feature achenes. Cardoons, cannabis, caraway, and roses also produce achenes. Some plants, such as the maple tree, produce modified achenes, called samaras. Other plants, such as wheat, barley, and other grains, produce a caryopsis, which is much like an achene, except that the seed coat is stuck to the pericarp. In the same way, each spike of a dandelion is a type of achene known as cypselae.
Scientists are still sorting out the details of this particular mode of seed life. Until recently, the individual seeds from sunflowers were considered achenes, but genetic research may be changing that decision. I’ll keep you posted.
Pea pods are just one example of the protective seed covering we call a pod. Most legumes and many Brassicas produce a long, dehiscent fruit that contains many seeds. [Dehiscent means that the structure opens spontaneously when its contents are mature.] Vanilla beans come in a pod, as well. But what makes a pod unique in the plant world?  Purple-podded peas Anatomy of a pod
A pod is made up of two identical long halves (bivalve) that contain seeds. These halves are joined and then split along a seam, called the suture. Legume pods are made from a single carpel, while Brassica pods (siliqua and silicula, depending on the pod dimensions) are made from two carpels. A pod’s purpose A pod protects the developing seeds. Pods can also perform photosynthesis, providing the seeds with food energy. Scientists have recently learned that pod tissue can recognize when a seed is damaged and relocate resources to where they might be better used. It ends up pods are major players in regulating seed development. Pod pests and diseases Plants invest a lot of energy into creating pods to protect their precious cargo. While bean seed beetles and other seed-chewing beetles may gnaw their way inside, and the pod spot (Ascochyta fabae), powdery mildew, and other fungal diseases may try to dissolve the pod, pods tend to be a strong defense for the genetic information they contain. The pods of beans, okra, peas, radish, and mustard are just a few of the edible pods you may have in your garden. And if you allow any of these plants to go through their complete life cycle, the pod will dry and split open, dispersing seeds where they fall, generating more plants for your foodscape! Trichome is one of those words you’ve probably never heard before, but you’ve seen what it means your whole life. Trichomes are plant hairs. Trichome can also refer to plant scales, such as those seen on the outside of pineapples. These hairs or scales can be seen on leaves or stems. Understanding the vocabulary related to trichomes can help you identify unknown plants.  Trichomes on borage  Sticky trichomes trap and begin digesting insects (Noah Elhardt) CC BY-SA 3.0 When a plant is covered with hairs, that covering is called an indumentum. The presence of trichomes provides a physical barrier against grazing, as in the case of nettles. In other cases, there is a sticky secretion that traps insects as food. Anatomy of trichomes Trichomes can be unicellular or multicellular. Unlike thorns and spines, which grow from shoots and leaves, respectively, trichomes are more similar to root hairs, both being outgrowths from epidural plant cells. Each of these cells, or groups of cells, may turn into thread-like extensions that can be long or short, stiff or soft, straight or curved. Some trichomes are glandular, meaning they secrete fragrant essential oils or toxic histamines. Plants with hairs or scales are called pubescent. If a plant lacks hairs or scales, it is said to be glabrous or glabrate. _lehekarv_(trihhoom)_311_0804.JPG) Electron micrograph of single-celled branching trichome (Heiti Paves) CC BY-SA 3.0 Types of trichomes Trichome hairs can be single strands or they can branch. These branchings can look like a tree (dendritic), star-shaped (stellate), or be tufted. There are different words used to describe the various forms of indumentum:
Take a closer look at your plants to see how they use trichomes to defend themselves.
Did you know that bean leaves have historically been used in Europe to trap bed bugs? Apparently, the spiky trichomes found on bean leaves puncture tiny bedbug feet, trapping them in place. In the world of plants, crown can mean two very different things. Like the fancy hat on a monarch’s head, crown can refer to the canopy of a tree. It can also mean the part of a plant slightly above and below the soil line. In both cases, the more you know about them, the better your plants will grow. Tree top crown Technically, the crown of a plant refers to everything that is above ground. Most people, however, use the term to describe the outer branches or canopy of a tree. In either case, mature crown size is an important factor when selecting a site for a tree. While most trees don’t mind mingling their branches, there are a few species that exhibit ‘crown shyness’ and will grow in such a way as to keep their distance from the branches of other trees. Tree crowns are classified by their shape. They can be rounded, weeping, funnel-shaped, spreading, pyramidical, oval, or conical.  David W. Lamb, et al (2016). Comparison of Canopy Volume Measurements. Remote Sensing, 8(5). Reproduced with permission of the authors. Leaves that make up the crown are responsible for far more than just photosynthesis. In addition to being the major food manufacturing system of the tree, they also filter out dust and other particles from the air, slow the speed at which raindrops hit the ground, and shade the ground below the tree, stabilizing soil temperatures for the root system. [Seven or eight trees also produce the oxygen you need to breath each year.] Tree crowns can be reduced moderately using heading cuts. Pruning in this way can lead to increased stem development lower in the tree, which means even more pruning to maintain air flow and sun exposure, while limiting the fruit load to a level that the tree can safely support.
In most cases, these diseases can be prevented with simple cultural practices:
Exceptions to the rule In some cases, transplants can be replanted deeply enough that the lowest set of leaves end up underground. These leaves should be removed at transplanting time. The nodes where the leaves were are then transformed into root tissue, increasing the availability of water and nutrients found in the soil. This practice is not recommended for most plants. However, tomatoes and peppers, in particular, can increase their yields substantially with this practice. I have heard mention of using the same technique on brassicas, such as cabbage and broccoli, but I could not find any verifiable proof, so I am skeptical until proven otherwise. As you walk through your garden, be sure to inspect the ground level crowns of your plants for signs of fungal disease and pests. Then, look skyward for a quick check on the overall form of your trees. These quick checks can reduce your workload and protect your plants over the long haul. Scapes are long, leafless flowering stems that grow out of a bulb or other underground structure. Scape or stem? Many people generalize that a scape is a flower stem, but it is not that simple. Botanically, a scape is a single internode, without leaves or branches, that either provides the base for, or becomes, the flower stem, or peduncle, and that it arises directly from an underground structure, such as a bulb, corm, or root. Most flower stems tend to emerge from twigs or spurs, instead. Which plants have scapes? In the world of edible gardening and foodscaping, scapes are the flowering stems of chives, garlic, onions, leeks, and scallions. The scapes of these edible plants can be eaten. The flavor becomes stronger and the scape becomes tougher as it matures, so scapes are normally harvested while still young and tender. Cyclamen, tulips, amaryllis, day lilies, and many succulents also feature a scape.
Each kernel of corn is a specialized type of fruit, called a caryopsis. So are rice, oats, barley, and wheat. Unfamiliar fruits Fruits are the seed-bearing structure of angiosperms (flowering plants), made from the ovary (pericarp) of a fertilized gamete. Fruits taste good because that makes them more likely to be eaten, spreading seeds far and wide. We are all familiar with fruits. Apples, peaches, olives, and avocados are all fruits, but so are cereal grains.  Oats and wheat Cereal fruits Unlike apricots and nectarines, which have thick, juicy fruit walls, cereal grains have a very thin, dry fruit wall, or husk. A caryopsis is a simple fruit. This means they develop from a single pistil. Because there is no seam to split open and release the seed within, it is called indehiscent. Botanically, the outer skin of corn kernels and grain seeds is the pericarp, or husk. The husk is firmly attached to the seed coat. That is why special milling processes must be used to get at those edible seeds.  Ransomes, Sims & Jefferies Ltd. advertising poster, The Museum of English Rural Life, The University of Reading, UK Public Domain Hulls, husks, and seed coats Hulls and husks are the same thing - most of the time. Looking at an ear of corn, the leafy outer coating is called a husk. Botanically, a husk, or hull, is another name for a seed coat. It can also refer to a pea or bean pod. These outer coats are removed using a process called threshing. Threshing is a brutal process (if you’re a grain). Mules and other livestock have been used to walk in circles on the grain, breaking it free of its hard outer coat.
Leaves come in a variety of shapes. Having a firm grasp of the vocabulary associated with leaf shapes can help you to identify and talk about plants more effectively. This is a HUGE subject, so, grab yourself a beverage and get comfortable. When describing leaf shape, some terms refer to the entire leaf, while others refer to specific parts of the leaf, such as the edge, tip, or base. Nearly all the terms are tied closely to the Latin word forms, so you are in luck if foreign language comes easily (or if you happen to already know Latin). Personally, I am not gifted in that particular area. Luckily for all of us, Latin is a pretty reliable language, when it comes to putting pieces of words together to make new words. .png) Leaf shape (Pearson Scott Foresman) Public Domain Don’t let all these new words scare you off, and don't expect to be able to remember everything. You can always return to this page, or use a field guide, when describing leaf shapes or identifying unknown plants. The important thing is to become familiar with the different ways that leaves are described and categorized.
Some leaves are shaped like a heart, kidney, fan, arrowhead, or spear:
Some leaves are shaped like a teardrop, while others look more like the silhouette of a violin, a spoon, a sickle, or a hand:
The Latin of lobes Some leaves have protrusions, called lobes, that can be rounded (like your earlobes) or pointed. Lobes can be arranged pinnately (in pairs) or palmately (like a hand). Lobes can be gently waving lines, they can be sharp incisions, or they can fall somewhere in between. These features are usually described as relative to the midrib line. Depending on the type of lobe a leaf might have, descriptive suffixes are added:
All about the base The way leaves attach to the rest of the plant can also provide clues for identification.
Here’s a tip At the other end of the leaf, tip shape can also provide clues for identification. Leaf tips can be:
There is a lot of variation in leaf tips:
Take it from the edge
The edge of a leaf is called its margin. Leaf margins provide an easy classification tool, since this trait stays consistent within a species. At the most basic level, leaf margins are:
If the stem attaches to a leaf near the middle, rather than at an edge, it is peltate. [Nasturtium] If it looks as though the stem passes through the middle of the leaf, it is perfoliate. [Miner's lettuce] You can find lots of online illustrations of leaf shapes, but, for right now, it has stopped raining and hailing and my garden is calling. Leaves nearly always appear singularly or paired. There’s nothing unusual about that, but the mathematics behind those arrangements may surprise you. Take a look at a stem or flower from above. You will almost always see distinct patterns in the way the leaves and stems are organized. These patterns are called phyllotactic spirals. Very often, Fibonacci numbers and the Golden Mean (or Golden Angle) are involved. Fibonacci numbers are a big part of nature and architecture. You can get a simple explanation at the bottom of my post on garden design.  Echeveria Leaf attachment Leaves emerge along a twig or stem at points called nodes. The space between each node is called the internode. Sometimes, in the angled space between the leaf and the stem, called the leaf axil, a bud may appear. The scaly covering on buds is actually made up of modified leaves, called bud scales. Note that only leaf buds have scales; flower buds do not. Where leaves emerge, along a stem, is determined by plant hormones, called auxins. Leaf arrangement At the most basic level, leaves emerge from a stem either individually or in pairs. Leaves that take turns up a stem, alternating from one side to the other, are called alternate. Leaves that appear in pairs are called opposite. Leaves growing close to the ground, around an upright stem, whether alternate or opposite, are called basal. Leaves arranged like an upright deck of cards are called two-ranked, or distichous [dis-ti-kus].
Leaf arrangement math
The fraction of a circle used to arrange leaves around a stem is very species specific. You don’t have to be a math whiz to understand this stuff, either. Let me explain:
Now look at leaf arrangement along and around a stem in the same way:
Are you with me? Hang in there! This stuff is amazing! So, since leaves and stems are different sizes, and species have different sunlight needs, there are different fractions, or ratios of rotation, around a stem. For example, hazel leaves are arranged in 1/3 (or 120°) rotations, apricots use 2/5 rotations, sunflowers and pears use 3/8, and almonds use 5/13. This means that the leaves of an almond tree are positioned 5/13th of the pie apart. If you do the math, this works out to 38.5° between each leaf attachment, as you work your way up or down a stem. This is where it gets really weird! The fractions that describe leaf arrangement are almost always made with a Fibonacci number and its successor, as the numerator and denominator, respectively. Now, the number of steps taken for a leaf arrangement to work its way around a stem, before repeating the pattern, is called its gyres. A three leaf cycle of rotation has one gyre, while a five leaf cycle takes 2 gyres. The number of gyres ends up being the numerator in the Fibonacci number that describes the rotation! Holy spring bulbs, Birdman! Whorls take this math to a whole new level The rotation of successive whorls is nearly always one-half the angle between the leaves. For example, say you have a whorled leaf arrangement that uses three leaves. From what we calculated above, there would be 120° between each of those leaves, along the length of the stem. All the other whorls will be half that distance, or 60° apart from each other. I have no idea why. Bottom line: whether leaves are alternate, opposite, whorled, basal, or distichous, the mathematics of leaf arrangement ends up providing each leaf with the optimal amount of sunlight. [If you really love this stuff, check out Gray’s Botanical Textbook: Structural Botany (1879)] Floral symmetry refers to whether or not, and how, a flower can be segmented into mirror images of itself. Flower basics Angiosperms (flowering plants) use a wide variety of structures, colors, and aromas to attract pollinators. These non-reproductive parts of a flower are called the perianth. The perianth consists of the petals (corolla) and the green cuplike structure at a flower’s base, called the sepals, or calyx. Looking at a flower from above, if you were to cut it in half, through the perianth, the two halves might be relatively identical, identical only along one plane, or not identical at all. These different types of symmetry are called radial, bilateral, or asymmetrical, respectively. Radial symmetry Snowflakes and apple pies have radial symmetry. No matter how you cut them in half, both halves look the same. Flowers with radial symmetry are called ‘regular’ or actinomorphic. Actinomorphic also refers to ‘regular’ star-shaped flowers that can be divided into three or more identical sections. Each section looks the same, no matter how you rotate the flower. Even though each half may not contain a complete petal, they are still considered actinomorphic.  Orange lily displays radial symmetry (Denis Barthel) CC BY-SA 3.0 Bilateral symmetry Most people have bilateral symmetry. This means our left and right sides look very much alike, but our fronts and backs look very different. Some flowers, such as orchids and snapdragons, are the same way. Some flowers have only one line that can be cut to create a mirror image. These flowers are classified as ‘irregular’ or zygomorphic. Zygomorphic flowers have bilateral symmetry and that line is called the sagittal plane. Lavender, olive, sage, mint, nasturtiums, basil, and rosemary flowers are zygomorphic. .jpg) Bee orchid displays bilateral symmetry (Hans Hillawaert) CC BY-SA 3.0
Flowers can be simple or compound, but don’t let the names fool you. Simple, or primitive, flowers, such as strawberries and geraniums, are actually more complicated than compound flowers. Simple flowers usually have 3 to 6 petals, sepals, stamens and pistils. Compound flowers, called inflorescences, are made up of hundreds or thousands of flowers, each with only one or two sepals and petals. To analyze compound flowers for symmetry, you would have to look at individual florets from that inflorescence. While sunflowers and dandelions may appear to exhibit radial symmetry, the actual florets may or may not be symmetrical, depending on the species.
Go take a closer look at the flowers in your garden. What sort of symmetry do you see? |
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