Heliotropism refers to a plant’s ability to track the sun’s movement.
For many centuries, it was believed that a plant’s tendency to follow the sun as it crossed the sky was a passive action caused by water loss on the side of the plant exposed to sunlight. Now, we know that there is far more to it than that.
Growing toward sunlight
Instead of passively shrinking to one side as the sun’s harsh rays boil away a plant’s bodily fluids, we now know that plants actively grow toward (or away from) sunlight. [When a plant grows away from sunlight, it is called skototropism.]
Experiments conducted in the 1800’s demonstrated that plants will respond to any type of light: street lights, grow lights, or sunlight. When plants are attracted to this light, it is called phototropism. Phototropism is a function of the hypocotyl, or individual cells found in the same region. Hypocotyls are the embryonic stem found below the seed leaves (cotyledons) and directly above the root. You can easily see examples of phototropism when seedlings first emerge and they don’t get enough sunlight - they become leggy and lean toward whatever light they can. This is phototropism.
In heliotropism, not any old light source will do. It is only radiation from the sun that causes the reaction. And the mechanical causes of these two types of movements are very different.
Mechanics of plant movements
When plants move in response to the position of an external stimulus, it is called a tropic [TRO-pic] movement. If a plant’s movement is independent of the stimuli’s position, it is called a nastic movement. In phototropism, plant hormones (auxins), found in the meristem tissue of leaf and stem tips, photoreceptors, and multiple signaling pathways are used to direct a plant to grow more rapidly toward sunlight. In heliotropism, a structure called the pulvinus is used to direct movement.
The power of pulvinus
The pulvinus is an amazing, fluid-controlled joint found at the base of a plant leaf stem (petiole) or just below a flower.
The pulvinus causes movement by altering fluid pressure in the surrounding plant tissue. These changes in fluid pressure start when sucrose is moved from the phloem into the apoplast. The apoplast is the conjoined spaces between plant cells. As sugar is pumped into the apoplast, potassium ions are pushed out, followed by water molecules. This changes the pressure within the affected cells, causing movement. This is called turgor-mediated heliotropism. But not all heliotropic flowers have a pulvinus. Those that do not are still able to move by permanently expanding individual cells. This is called growth-mediated heliotropism. Pulvini are also used in response to nyctinastic and thigmonastic movements.
Heliotropic flowers face the sun from dawn to dusk. Slowly tracking the sun’s path across the sky, these flowers are believed to use heliotropism as a way to improve pollination, fertilization, and seed development. Heliotropic flowers often have five times as many beneficial insects present, due to the added warmth. [Many tropical flowers exhibit a modified form of heliotropism in which flowers maintain an indirect tracking of the the sun. This is believed to reduce the chance of potential overheating.] Beans, alfalfa, sunflowers, and many other species turn their blooms to follow the sun’s path across the sky each day. But sunflowers only use heliotropism in their early development, in the bud stage. Once a sunflower head emerges, it may track the sun for a short time, as an expression of phototropism, until the flower head reaches full size. The majority of sunflowers found in the northern hemisphere nearly always end up facing east.
Like floral heliotropism, leaf heliotropism is the method by which plants focus their leaves perpendicularly to the sun’s morning rays (diaheliotropism), or parallel to midday sun (paraheliotropism). Diaheliotropism allows leaves to capture the maximum amount of energy from the sun, while diaheliotropism protects plants from overheating and dehydrating.
How do your plants move during the day?
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.
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.
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.
Most fruits hang in their own singularity: apples, oranges, and apricots are common examples. Other fruits, such as grapes, form clusters. Still other fruits are formed when a group of flowers merge to create a fruit. Soroses are that type of fruit.
What is fruit?
Fruit is the fertilized ovary of a flowering plant (angiosperm). After pollination and fertilization occur, two new structures are produced: seeds (fertilized ovules) and pericarp (thickened ovary walls). In the case of apples and oranges, one flower produces one fruit. Sometimes, multiple flowers can fuse together to create a fruit. There are three different ways that this can happen:
In nearly every piece of literature you see, pineapples are listed as a common example of sorosis, but this is incorrect. I don’t know why they do this.
How a sorosis fruit develops
If you look at a mulberry flower cluster, you will see several flower buds held tightly together. Each of these individual flowers open up, awaiting pollination.
If you look closely, you can see tiny fruits at the base of each flower. Each of these fertilized fruits will develop around the stem that they emerged from in the first place. This is unlike pineapples, which include the receptacles and flower parts in their fruit development.
Berries vs. soroses
While mulberries may appear to have the same structure as blackberries and raspberries, botanically, they are quite different. Raspberries and other members of Rubus are made up of several drupes (a type of fruit) that are clustered around and attached to a dry thalamus. All of the drupes in a single fruit are made from a single flower. In mulberries, and other soroses, each rounded bit is its own fruit, formed from its own flower.
It won’t make any difference, as you enjoy a fig, some pineapple, or a mulberry, but now you can impress your friends with this fascinating word!
Some garden words are fun to say. Schizocarp [ˈskitsōˌkärp] certainly qualifies.
A schizocarp is a type of dry fruit that splits into single-seeded parts, called mericarps, when ripe. Each mericarp is made from its own carpel. [A carpel is the female reproductive parts of a flower, including an ovary, stigma, and usually a style.] Mericarps can be dehiscent, which means they split open when ripe, or indehiscent, which means they stay closed.
The seeds of carrots, celery, coriander, anise, dill, parsnip, and other umbellifers are all indehiscent schizocarps. Hibiscus (Malvaceae), mallows and cheeseweeds (Malva), false mallows (Malvastrum), and wireweed (Sida acuta) fall in the same category.
Members of the Geranium genus produce dehiscent schizocarps. [These are not the garden variety geraniums, which are another genus altogether (Pelargonium). I know, I know, it gets confusing.] True Geranium species include the cranesbill, horns’ bill and filaree plants that produce needle-shaped schizocarps that twist and gyrate into the soil (and were fun to play with, when we were children).
Maple trees produce winged schizocarps, called samaras.
Unlike the juicy fruits we enjoy each summer, or the dried caryopsis of cereal grains, plants that produce schizocarps have found that procreation works best when each flower produces a number of independent seeds protected by a dried fruit coating.
Now you know.
Plants cannot be green without magnesium, but too much magnesium in the soil can turn plants yellow. How can this be?
Magnesium is essential for plant health. Magnesium stabilizes cell membranes, making plants better able to withstand drought and sunburn. Magnesium is found in enzymes that plants use to metabolize carbohydrates. Most important, magnesium is contained in the chlorophyll molecules that convert the sun’s energy into food. This process, the Calvin Cycle, is what makes photosynthesis possible. Clearly, magnesium is important to plant health. But too much magnesium can interfere with the absorption of other plant nutrients.
Plants use 13 dissolved minerals as food. There are three primary macronutrients (nitrogen, potassium, and phosphorus) and three secondary macronutrients (calcium, sulfur, and magnesium). Plants use large amounts of these macronutrients to grow, thrive, and produce. Seven other nutrients, used in smaller amounts, are called micronutrients. Fertilizers claim to provide all the food your plants need, but it’s not that simple. [Is it ever?]
The chemical interplay, taking place in the soil, that allows plants to absorb nutrients, is a delicate balancing act. Too much, or not enough, of one nutrient can create a domino effect that causes starvation for plants that are surrounded by a banquet of nutrients.
What is magnesium?
Magnesium is an elemental metal. Pure magnesium (Mg) is too stable of a molecule for plants to absorb. The less stable, cation form of magnesium (Mg2+) is a dissolved salt that plants use for food. To be able to attract and hold those positively charged molecules, plants also need negatively charged molecules (anions), such as nitrogen, phosphorus, and sulfur. The ability of soil to perform this balancing act is called its Cation Exchange Capacity (CEC). Without a soil test from a reputable, local lab, you cannot know your soil’s CEC or nutrient levels.
For example: My first soil test found magnesium levels of 798 parts per million (ppm). The ideal range is 50 to 120ppm. Clearly, before I moved in, someone was applying an awful lot of fertilizer. The problem they were probably trying to correct was not insufficient nutrients, but a nutrient imbalance. Without a soil test from a local, reputable lab, you simply do not have enough information.
Base saturation and magnesium
Soil test results also include base saturation figures for potassium, calcium, and magnesium. Base saturation is the percentage of available connections being used. [Think of it as how many grocery bags you can carry in from your car.] The optimal range for magnesium base saturation is 10 to 30%. This means that soil particles, because of their electrical charge, will ideally hold on to 10 to 30% of the magnesium in the soil. It takes the right absorption percentage and the right volume of magnesium in the soil for plants to be healthy.
My soil’s magnesium base saturation was 32%. That sounds close enough to the 10 to 30% optimal range, right? The problem is, with seven times the amount of magnesium needed in the soil, my plants were getting 32% of too much.
Too much magnesium in the soil makes it difficult for plants to absorb calcium and other anion nutrients, which can lead to blossom end rot, bronzing, and many other problems. This is a common problem in areas with alkaline soil. The opposite is true in areas with acidic soil. Insufficient magnesium symptoms look very much like potassium toxicity symptoms: older leaves, at the bottom of the plant, start turning brown, between and alongside the leaf veins, working upward through the plant. Magnesium deficiencies in stone fruits often start out as slightly brown areas along leaf edges (margins) that expand inward, causing cracking, necrosis, and leaf loss. Magnesium deficiency in California is extremely rare.
Stabilizing magnesium levels
Reaching and maintaining ideal mineral levels in soil for healthy plant growth is both science and art - mostly science. To start, get a soil test from a local, reputable lab. Unfortunately, over-the-counter soil tests are not yet accurate enough to be useful. Once you have your results, you can take these other factors into consideration:
Finally, schedule regular soil tests for your garden and landscape. Look at these tests as an annual physical for the living skin of your property. The information in these tests will help you make informed decisions about the magnesium in your soil.
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.
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.
What is latex?
Latex is an emulsion made up of of proteins, fats, starches, sugars, oils, resins, alkaloids, tannins, and gums. Emulsions are mixtures of two or more liquids that generally do not mix - think salad dressing. Homogenized milk and mayonnaise are also emulsions. Normally, latex is thick and white, but it can also be yellow, clear, orange, red, or watery.
How is latex different from sap, or resin?
Sap is the combined water, sugars, and plant nutrients that move through a plant’s vascular bundles to feed and water the plant. Resins, like latex, are protective substances that ooze from injury sites. Unlike latex, which coagulates and dries, resins create a hard, crystalline barrier.
How do plants make latex?
Latex is produced and transported in a separate system called the laticiferous system. There are two methods of latex formation and movement. Articulated laticifers consist of rows of plant cells found in the meristem tissue of stems and roots. The walls of these cells dissolve, creating tubes, called latex vessels. This method is common to poppies, fig trees, mulberries, rubber trees, and members of the sunflower family. Non-articulated laticifers, such as milkweed and spurge, develop a branching network of latex-producing cells throughout the plant. In some cases, the entire network is made from a single cell.
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, as can multiple surgeries, or spina bifida. 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. These forms are being researched as an alternative.
As you work in the garden, note which plants exude latex when damaged. And monitor your skin for reactions to this liquid plant defense.
How would you like a garden or landscape filled with plants for free?
Rather than buying seeds and seedlings, digging furrows, rows, and hills, planting and watering those seeds and seedlings, and hoping for the best, you can let nature takes its course and grow a surprising number of self-seeding vegetables, herbs, and flowers without any help from you.
What is self-seeding?
Plants classified as self-seeding are usually annuals or biennials that tend to produce a large number of viable seeds, pods, or capsules. These seeds fall to the ground, where they then start a new crop of the same plants (called volunteers) within the immediate (and not-so-immediate) area, during the next growing season. All this productivity occurs without any human intervention. As an added advantage, self-seeding plants provide more pollen and nectar for local pollinators and other beneficial insects than would otherwise be available, and for a longer period of time.
Self-seeding plant selection and placement
Self-seeding plants come in all shapes, colors, and sizes. Aeoniums, borage, marigolds, nasturtiums, poppies, snapdragons, sunflowers, sweet alyssum, and zinnias and are all self-seeding. Before installing a self-seeding plant, however, be sure to check with your local extension service to make sure it is not an invasive plant. Also, be sure to select a location suitable to long-term growth. You can introduce self-seeding plants into an area for free simply by tossing a seed head from a mature plant into the area. The seeds will take care of themselves, providing a new crop during the next growing season.
Allowed to follow their natural lifecycle, many popular garden vegetables will bolt and produce hundreds of seeds. While many of these seeds will rot or be eaten by birds and other critters, you will end up with more seedlings than you know what to do with. (Give them to neighbors, family, and friends, Plant It Forward style). A surprising number of vegetable plants readily self-seed, as long as your winters are not too cold:
While these offspring are not always true to their parent plants, especially in the case of hybrids (names that include F1), I have found they are always delicious and edible! Open-pollinated heirlooms are more likely to look, grow, and taste like their parents.
I have maintained the same four beet plants, two yellow, one white, and one red, for several years, for seed production. As a result, I have beets turning up everywhere! And the parent plants add changing shapes, sizes, and colors throughout the seasons. Endive and several lettuces are now naturalized in my foodscape. By naturalized, I mean that the plants turn up wherever they take hold. At first, they are low-growing mounds of salad deliciousness. Then, in mid-spring, a central stalk appears, drawing the plant upward in a cone shape that ends up bearing lovely blue and white flowers. After the seeds have been dispersed, I cut the plants off at ground level and feed them to my chickens. Next winter, new crops of endive and lettuce appear like clockwork, with no effort on my part. I transplant some of these volunteers to create lovely borders and accent plants. And they don’t cost me a dime.
Many herbs are also self-seeding. Basil, chamomile, chives, cilantro/coriander, dill, fennel, lemon balm, oregano, parsley, and sorrel, are just a few favorite herbs that willful an area without any help from you. Parsley, in particular, is a super seed producer. A single parsley plant can produce the equivalent of 10 seed packets! For free!
The very characteristics that make self-seeding plants so successful can also make them troublesome. Some self-seeding plants can take over an area, much the way mint plants do. Also, if a plant is prone to certain diseases, such as powdery mildew or blight, or susceptible to insects commonly found in your garden, you might need to incorporate crop rotation to break the disease triangle, or insect life cycle. If you really want them, these self-seeding plants are best corralled into containers and deadheaded frequently.
If your self-seeded volunteers turn up in undesirable locations, you can always transplant them into a more suitable or convenient spot, pull them by hand as seedlings, or mow any that turn up in a lawn. If your winters are too cold to allow self-seeding to occur naturally, you can always collect seeds from these abundant producers and use them to start next year’s crops.
Lighten your work load and increase biodiversity in your garden and landscape with self-seeding vegetables and herbs!
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.
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.
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.
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.
You can make clones of many favorite plants for free with layering! Layering is a form of vegetative propagation.
Unlike other vegetative propagation methods, such as cuttings and division, layering allows the parent plant to continue providing water and nutrients to their offspring as they develop their own root system. This is because they are still attached!
Strawberry runners are an example of natural propagation by layering. The parent plant sends out runners. Where the nodes touch soil, adventitious roots emerge and a new root system begins to develop. As it does, the parent plant continues to support this newly developing clone. Once the offspring are self-sufficient, the runner stem eventually dries up and falls away. Layering uses the same basic idea by pulling a stem downward until it touches the soil at what would have been a leaf node. Coming into contact with moist soil, the plant reprograms that node to become root tissue.
Many window sill gardens are populated with herbs, such as rosemary, sage, and lavender, that are easily propagated with layering. In some cases, plants are wounded on one side, to stimulate rooting. In other cases, the stem is bent sharply at the point where it touches the ground. The most critical point in layering is that the soil must be kept moist as the new roots grow. If the growing medium dries out, the process fails. In some cases, this process is complete within the first year. In other cases, it can can 3 or 4 years, so be patient. Some people use rooting hormones (auxins) to speed things up.
There are six different types of layering:
Air layering Air layering is used predominantly on thick-stemmed houseplants that have become leggy. It is also used to generate new trees and shrubs, including apple, blueberry, citrus, cashew, cherry, fig, kiwi, pear, pecan, and walnut! Stems are slit just below a node and the slit is pried open. Th wound is then wrapped with wet, unmilled sphagnum moss and wrapped with plastic, which is tied in place. When new roots fill the moss, a cut is made below the root ball, separating it from the parent plant and replanted elsewhere.
Compound (serpentine) layering Compound layering is best suited to plants with flexible stems, such as pothos. Stems are bent into rooting medium in a serpentine arrangement that allows several nodes to begin developing their own root system. Again, some people wound the area that ends up below ground to stimulate rooting.
Mound (stool) layering Mound layering, also called stool layering, is used primarily on woody plants to stimulate rooting of new shoots. During the dormant season, the plant is cut back to one inch above ground level. Soil is then mounded over the new shoots as they emerge in spring. This method is best suited for apple and plum rootstocks, and gooseberries.
Simple layering Simple layering consists of bending a stem down to the ground and covering it with soil, leaving the last 6 to 12 inches exposed. This tip is bent into a vertical position and staked in place. Wounding the area that ends up underground can stimulate rooting. This method is best suited for hazelnuts, forsythia, and honeysuckle.
Tip layering Tip layering is a method commonly used on cane fruit, such as blackberries and raspberries. Tip layering consists of digging a small hole, 3 or 4 inches deep, and putting the tip of a cane into the hole and covering it with soil. At first, the tip will grow downward. Then, it will complete a U-turn in the soil and emerge aboveground. That bend will develop roots, allowing the new plant to be separated from the parent plant in spring and replanted elsewhere.
Trench (etiolation) layering Trench layering, or etiolation layering, is generally used to create fruit tree rootstock and grape vines. In this method, parent plants are planted at a 30 to 40° angle. As new shoots emerge, they are pulled down into shallow trenches, pegged in place, and covered with soil until new roots emerge.
Layering is an easy way to make new plants out of existing favorites, without spending any money!
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.
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?
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.
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.
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 bedbugs? Apparently, the spiky trichomes found on bean leaves puncture tiny bedbug feet, trapping them in place.
Is it true that melons and squash can cross-pollinate? If I plant a lemon tree too close to an orange tree, will the oranges be sour? You’ve heard of cross-pollination, but what does it really mean and do you have to worry about it? Let’s start by reviewing pollination.
Pollination and fertilization
Pollination refers to the act of pollen, the male genetic information (gametophyte), moving from the anther to the (female) stigma. From there, the pollen grain grows a pollen tube, which makes its way down the style to the ovary. Two sperm cells (gametes) then move through this tube to fertilize female gametes. One male gamete fuses with a female gamete to produce an embryo, while the other fuses with a different type of cell, called a polar body, to form the endosperm, which will feed the developing embryo. [You can think of these two much like the yolk and white of an egg, respectively.] Since two fertilizations are actually occurring, it is called double-fertilization, but I digress.
Types of pollination
Pollination can occur one of two ways: self-pollination or cross-pollination. Self-pollinating flowers pollinate themselves. Cross-pollination, or allogamy, refers to the way pollen moves from one plant to another of the same species. Wind and insects, such as honey bees, are the main perpetrators of cross-pollination. Natural cross-pollination can only occur within a species (we will not discuss genetic manipulation at the nano surgery level).
To give you a clearer idea, consider this: Horses breed with horses. Donkeys breed with donkeys. When a female horse breeds with a male donkey, their offspring, a mule, is nearly always infertile. The same is true in the plant world.
This means that zucchini plants can cross-pollinate with pumpkins and other summer squash varieties, but not with melons or cucumbers. This is because squash and pumpkin are both members of the Cucurbita pepo species. In the same way, cucumbers (Cucumis sativus) cannot cross-pollinate with muskmelons (Cucumis melo). Their genetic information doesn’t match up properly.
When cross-pollination within a species does occur, the offspring (seeds) are often useless, but it has no affect on the current season’s fruit or vegetable. The only exception to that rule is sweet corn. When varieties of sweet corn cross-pollinate, the current season’s crop will exhibit characteristics of both species. In nearly all other cases, it is the DNA found in seeds that is altered. If you save seeds for next year’s crop (and I urge you to do so), you will grow plants with characteristics of both parent plants. This is how we get many new cultivars with desirable traits or unique properties. The only way to prevent cross-pollination is to keep crops 100 yards or more apart, which probably isn't realistic in your home garden. You can reduce the chance of cross-pollination by keeping plants as far away from each other as possible.
The science of genetics owes its start to cross-pollination among common pea plants
and a central European monk, named Gregor Mendel, back in the mid-1800’s.
Most of us grew up learning about how pollen sticks to bees as they go from flower to flower, collecting nectar and pollinating many common food crops. But that’s not how it works for your tomatoes and peppers. Instead, they use buzz pollination.
Buzz pollination video (PBS)
Most flowering plants (angiosperms) have male parts, called anthers, that have pollen on the outside, available to all takers. This pollen held in place by its extreme stickiness. [That stickiness is why you need to use soap and water to get pollen off your face and eyelashes, for those of you who are prone to allergies.] This pollen can be knocked loose by busy pollinators and then carried on the wind, or the pollinators find themselves covered with the sticky stuff, as they move from flower to flower, feeding on nectar and collecting pollen.
Dry, dusty pollen
Some flowers don’t have sticky pollen. Instead, they have pollen that is dry and dusty. If that pollen was exposed, it would all be gone with the first breeze, most of it never making it to another flower. Instead, these plants have evolved a specialized type of anther, known as a poricidal anther. Poricidal anthers are tubes with tiny openings at one end, but these openings are too small for bees to use. To make matters worse, these plants generally do not offer nectar, so how do they get pollinated?
Pollination by vibration
Approximately 8% of the world’s flowers are only pollinated when the correct sound wave frequency occurs nearby. When it does, the flower explodes a small dose of pollen into the air, coating whatever is at hand with genetic information and protein-rich food. This is called buzz pollination, or sonication. It gets those names because certain insects that have learned how to buzz at just the right frequency to trigger these plants to share their bounty.
These flowers release pollen at frequencies between 40 to 1000 Hz, depending on the species [You can use a tuning fork or an electric toothbrush to try this for yourself.] Scientists believe this arrangement evolved as a means to ensure that each visiting pollinator carries away a smaller portion of pollen (which they are less likely to drop on their way to the next flower) and that those portions are spread out over a greater number of pollinators, and over a wider time frame, for better odds of procreation. How’s that for evolution?
Not honey bees
Honey bees do not use sonication to get at pollen, but several other bees do. Sweat bees, carpenter bees, and bumblebees all use buzz pollination to get at the pollen held in poricidal anthers. They do this by disconnecting their wings from their flight muscles [I have no idea how they do this!] and vibrating those muscles at just the right frequency. In most cases, this frequency is close to middle C. The force generated during sonication can reach 30 Gs, which is almost more than a human can tolerate!
Which plants use sonication?
You may be surprised to learn that many common garden plants use sonication. Members of the legume and nightshade plant families frequently use buzz pollination to generate the fruits and vegetables we love. In addition to tomatoes and peppers, other edible plants that use buzz pollination include eggplants, potatoes, peas, blueberries, tomatillos, and kiwi.
How are your flowers being pollinated?
In the world of plants, crown can mean two very 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.
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.
Ground level crown
The ground level crown is where the shoots, stem, or trunk meets the root system. Very often, when a root stock is grafted to a fruiting stock, this is where the graft will occur. If you look closely, you should be able to see a grafting scar. Grafted or not, the crown is a vulnerable area. Fertilizer, mulch, and standing water should be kept away from the crown. It is much better for your tree’s health to irrigate and fertilize closer to the drip line. The drip line is the outer edge or silhouette of the overall tree.
Being exposed to water and soil, the crown is susceptible to fungal infestation and other problems. Some of the more common pests and diseases of the crown area (and their hosts) include:
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 under ground. 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.
Edible garlic scapes
While garlic plants do not produce flowers, they do grow flower stalks, or scapes. Garlic scapes are normally removed by gardeners because the scapes use nutrients that could be going to the underground bulb. This is true of hardneck garlic, in particular. As an added bonus, these garlic scapes are delicious! If left on the plant, these scapes will result in the development of tiny bulbs, called bulbils. These bulbils can be planted to create the next generation of garlic.
Have you harvested garlic scapes before? Tell us about it in the comments!
Each kernel of corn is a specialized type of fruit, called a caryopsis. So are rice, oats, barley, and wheat.
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.
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.
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. In some regions, grain is spread on roads to be threshed by cars and trucks. Traditionally, the dried fruit husk was removed using a flail.
After the grain was threshed, it had to be winnowed. Winnowing uses wind to separate the grain from the dried fruit hull, or chaff.
Maybe, if we had to do all that work for our grains, too many carbs wouldn't be such a problem....
Once the dried fruit covering is removed, the remaining seed is called a groat. If that groat is parboiled, it is then called bulgur. Now you know.
We don’t know why certain flowers tuck themselves in at night, or why some leaves fold themselves together as the sun sets, but we know how they do it. These openings and closings of petals and leaves is called nyctinasty [nik-TIN-as-tee]. Nyctinastic movements are also called sleeping movements.
Options in plant movement
While plants are not free to get up and walk around, they do have options when it comes to movement. Some plants follow the sun’s movements across the sky, in a behavior called phototropism. There are also rare individuals who exhibit skototropism by moving away from sunlight. Note that both of those words end with -tropism. Movement is tropic [TRO-pic] if it is in reaction to a source of stimulus. Tropic movement is nearly always growth related and it is dependent on the direction of the stimulus. If a plant’s reaction is independent of the stimuli’s position, it is called a nastic movement. Nastic movements may or may not be growth related. If you see a plant behavior word that ends with -nasty, you will now know that it is a nastic behavior. Nyctinasty is one of those words.
Latin bed times
We all have our bedtime routines. Some plants do, too. These routine behaviors are called nyctinastic. You just learned that -nastic means movement independent of a stimuli’s position. When it happens because of nighttime, we add the Latin prefix nyct-, which means ‘at night’. Put the Latin for non-directional reaction to nighttime together and you get nyctinasty.
YouTube video by Joshua Puzey
Why do flowers close at night?
We don’t know. Charles Darwin thought that nyctinasty was used to protect against freezing. Some scientists theorize that it has to do with pollination and reducing competition, or protecting nectar from bacteria and fungal spores. Other possibilities include saving up aroma molecules for when they will be most effective, energy conservation, or as a means to prevent pollen from getting wet. Wet pollen is heavy and insects are less likely to carry as much, potentially reducing pollination rates. Yet another theory is that nyctinastic flowers and leaves close up shop to prevent being eaten by nighttime herbivores. The truth is, we don’t know why. We do know, from laboratory tests, removing the gene that causes nyctinasty results in plants with smaller leaf areas and reduced biomass. We may not know why they do it, but we do know how they do it.
How flowers and leaves open and close
Several different flowers, such as tulips, dandelions, crocuses, and daisies, and the leaves of many legumes species, open each morning and close each night. Some flowers, particularly the Kalanchoe genus, grow new or longer cells each morning, on the inside of the flower, to open it, and on the outside of the flower each evening, to close it. Other flowers, and most nyctinastic leaves, rearrange fluids within the plant to cause these movements. This movement of fluids is a reaction to changing temperatures and light frequencies.
Movements of liquid and light
Nyctinasty is triggered within a plant in response to changes in external light, temperature, and humidity, and an internal circadian clock. As the sun sets, light frequencies change and temperatures drop. The shorter wavelength and higher deflectability of blue light gives way to longer, less readily deflected red wavelengths, and lower temperatures. The reduction of blue light triggers blue-green pigments (phytochromes) to rearrange potassium ions within the plant. This rearrangement of ions pulls water along with it, causing turgor. Turgor refers to rigidity that is normally caused by the presence of fluids.
So, as dawn arrives and temperatures start to rise, interior cells grow faster, or are inflated with water, to push open your flowers. At days end, outer cells grow longer and faster, or internal cells are deflated, and the flowers close for the night. This is nyctinasty.
Endophytes are tiny heroes of the garden.
You rarely see them with the naked eye, but most of these tiny organisms work hard to protect our plants.
What are endophytes?
The word ‘endophyte’ literally translates as ‘in the plant’ (‘endo’ = within; ‘phyte’ = plant). Endophytes are tiny organisms that live inside plants, for at least part of their life, without causing disease. In most cases, they provide a benefit to the host. The plant returns the favor by providing the endophytes with carbon [sugar]. Endophytes can be fungal, bacterial, or viral, or they can be other plants. Endophytes are everywhere and they can occur in any place within a plant.
Some endophytes grow between plant cell walls, while others live inside plant cells, and they tend to grow at the same rate as their host. Researchers have learned that plants and their endophytes use chemical signals to communicate with each other. These communications determine which helpful chemicals and what quantities are needed by both sides of the arrangement.
The science behind endophytes is relatively new. Because of this, the definitions are still being sorted out. Some scientists include parasitic and pathogenic organisms as endophytes, while others focus on the beneficial, or mutualistic forms. That’s where I stand, for now. There are several different ways that endophytes help their host plants.
Certain endophytes help plants get the food they need. The rhizobium bacteria that helps legumes fix atmospheric nitrogen is a type of endophyte. Other endophytes break down rock phosphate within the soil, making it absorbable to plant roots. Some scientists categorize mycorrhizae, or root fungi, as a type of endophyte, while others do not. [Isn't it exciting, being on the crest of new scientific research?]
Endophytes have been shown to enhance overall plant growth. They do this by improving a plant’s tolerance of abiotic stresses, such as drought, heat stress, water stress, salinity, and poor soil. When allowed to grow naturally, these mutually beneficial arrangements make both parties stronger. Unfortunately, the use of fungicides interferes with endophyte development. Also, the use of fertilizers reduces a plant’s reliance on its resident endophytes. This is, theoretically, fine, as long as the fungicides and fertilizers continue to be supplied. As soon as these artificial treatments are withdrawn, however, host plants are left with less food and protection.
Commercial agriculture is slowly coming around to the long term benefits associated with these natural arrangements, but you can take advantage of it in your own garden right away by avoiding the use of chemical fertilizers and fungicides.
Did you know that when you inoculate legumes, you are putting endophytes to work for you in the garden? Now you know!
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.
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.
Leaf and leaflet silhouettes
Leaves are first identified by their overall shape. They can be round, triangular, oval, rectangular, or diamond-shaped:
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. [Miners lettuce]
I will be adding more images and examples of different leaf shapes in the near future but, for right now, it has stopped raining and hailing and my garden is calling.
How many different leaf shapes can you identify in your garden?
You can grow a surprising amount of food in your own yard. Ask me how!