Ferns look lovely in a stumpery, but there is surprisingly more to ferns that you might expect
These plants have been around for over 350 million years, long before flowering plants, or angiosperms, made their appearance. Or dinosaurs, for that matter! Ferns are vascular plants that do not produce flowers or seeds. Instead, they reproduce using spores, similar to mushrooms and other fungi.
There are over 10,000 known fern species of fern [so far] and some species can live for 100 years. While some ferns are nearly microscopic, others can reach 80 feet in height.
There is a group of ferns (Azolla) found predominantly in water and they do not look like any ferns you might see on land. One in particular, the mosquito fern, is able to fix atmospheric nitrogen the same way land-dwelling legumes do before going to seed.
Ferns have three basic parts: rhizome, fronds, and sporangia. Fern rhizomes come in three forms: erect, lateral, and vertical. Erect rhizomes provide the solid base from which leafy fronds unfurl. Laterally growing, creeping rhizomes move above and below ground and may even climb trees. Vertical rhizomes often look more like the trunk of a tree.
Fronds are a fern’s leaves. The leaf stem, called a petiole when referring to other types of plants, is called a fern’s stipe. The flat blade of the frond is called a lamina. The lamina is often segmented into pinnae by short stems called rachides. When a frond first appears, it is tightly curled and called a fiddlehead or koru. Fronds perform photosynthesis and they provide support for a fern’s reproductive sporangia.
Black, brown, or orange sporangia are the reproductive structures of ferns. If there are no sporangia present, the fern is sterile. Normally found on the underside of the fronds, spores are formed in the sporangia. A cluster of sporangia is called a sorus. In some cases, a flap of tissue, called the indusium, may cover the sori until the spores are mature.
Ferns are unique in their method of reproduction and they are the only plants with two distinct living stages. As each spore matures, it becomes a sporophyte. Sporophytes that land in hospitable environments grow into very tiny, short-lived plants called gametophytes. Gametophytes have two sets of reproductive organs: a female archegonia and a male antheridia. Fertilization can take place within the same plant or between two neighboring plants. This fertilization produces a new sporophyte that grows into an adult fern.
While most ferns are not considered edible, they also tend to not be poisonous. There are some varieties of fern that are edible, such as:
As always, do not eat anything you are not sure to be safe.
Fern pests and diseases
Ferns are naturally resistant to most plant-eating insects. One edible fern in particular, Tectaria macrodonta, has a gene that was transferred to cotton plants, providing resistance against whiteflies! Foliar nematodes (Aphelenchoides fragariae) and soil borne nematodes (Pratylenchus) can sometimes be a problem.
Ferns are susceptible to diseases such as bacterial blight (Pseudomonas cichorii or P. gladioli), Pythium root rot, and Rhizoctonia blight. Infected plants should be discarded. Environmental problems, such as drought, which causes greying, and over-fertilization, which results in frond lobing and leaf tip burn, can be avoided with good cultural practices. This means investing in disease-free plants, using only as much fertilizer as recommended for each fern species, and avoiding overhead watering.
If you have a moist, shady crevice in your garden, ferns might be just what you've been lookin for!
Heartwood is the dead center of a tree. It is usually a different color from the living wood and it provides the support needed to hold up a tree that might weigh several tons
Tree trunks are made up of several layers of tubes, surrounded by an outer layer of bark. These tubes are the vascular bundles that carry water and nutrients to the rest of the tree. One type of tube, called the xylem (or sapwood), pulls water and nutrients up from the roots. The majority of the trunk is made up of xylem cells. Another type of tube, called the phloem (or inner bark) carries the sugars made by the leaves through photosynthesis down into the rest of the tree. [I remember these two by saying, “Food flows down the phloem, while water and food rise in the xylem.”]
Just between the xylem and the phloem is the cambium layer. This is where the actual tree growth occurs. At the very center of the tree is the pith, surrounded by layers of xylem cells. As these xylem cells age, they eventually go through chemical changes that make them solid, losing their ability to transport water and nutrients. There is debate about whether or not these cells are still alive. This is the heartwood.
Characteristics of heartwood
Heartwood is very strong. The amount of heartwood present depends on the species. Some trees, such as ash, maple, and pine, have very thick heartwood. Other species have only a little heartwood. This group includes chestnut, mulberry and sassafras trees. Some tree species have no heartwood at all.
Heartwood gets larger over time. Young trees have very little heartwood, whereas older trees have significantly more.
Heartwood is resistant to decay, but wood that looks like heartwood might also be infected with disease or dealing with an insect invasion. Louisiana homes built over 100 years ago out of of bald cypress heartwood appear to be as good as new because of the decay resistance of heartwood.
The next time you need to remove a large branch or tree trunk, take a closer look at the layers and see if heartwood is present.
If you have ever canned jelly or fruit preserves, you have probably used pectin. Pectin is found in many plants and it has some unique properties.
The word pectin comes to us from the Greek word for “congealed” and with good reason. Pectin converts liquids into jelly, much the way gelatin does, the difference being that gelatin is made from animal skin and bones, and pectin is made from plants.
Pectin is found in most fruits, to one degree or another:
But fruits are not the only plants that contain pectin. Carrots hold an average 1.4% pectin. Commercially, most pectin is made from citrus peels and apple pulp. Soft fruits, such as grapes and strawberries also contain pectin, but at very low levels.
How do plants use pectin?
Pectin is a structural chain of molecules used in cell walls. Pectin is a major component of cellulose, specifically a layer called the middle lamella. The middle lamella is an outer layer to plant cells that is used to bind cells together. This allows plants to grow larger. The level of pectin present in a plant varies over time due to factors such as plant age and seasonal changes.
As fruits ripen, the pectin begins to break down, which is why the fruit becomes softer. A similar process occurs during abscission, when parts such as leaves naturally die and fall from the plant. In some desert plants, pectin has been shown to help repair DNA by creating a mucous layer that captures dew.
How do we use pectin?
Pectin is used for more than jelly making. Pectin also provides dietary fiber and it acts as a thickening agent and stabilizer for desserts, cosmetics, and medicines. Pectin also binds to cholesterol and slows the rate at which we absorb glucose. This is especially true when the pectin is from apples and oranges. You know that old saying about an apple a day? I guess they were right!
The pectin found in apple pulp is also one of the best throat lozenges I know. The mucilaginous pectin provides a surprising amount of soothing relief. Next time your have a sore or scratchy throat, skip the menthol (an irritant) and slowly eat an apple.
Molybdenum (Mo) is a plant micronutrient. So little is used that they used to be called trace minerals, but that doesn’t mean they are not important. Molybdenum is very important to your plants’ health.
Generally speaking, molybdenum is plentiful in alkaline soils and tends to be deficient in acidic soils. You can’t know what your soil contains without a soil test from a reputable lab. Those cute, colorful kits from the garden center don’t even test for molybdenum. Even if they did, they are not [yet] accurate enough to be useful.
How plants use molybdenum
Molybdenum is an essential ingredient to some very important enzymes. These enzymes are used in nitrogen, oxygen, and sulfur cycles. Specifically, molybdenum is used convert nitrate into nitrite and then into ammonia in order to be used to synthesize amino acids. It is also used by the bacteria responsible for converting atmospheric nitrogen into forms usable by plants. Molybdenum is also part of the process that converts inorganic phosphates into organic ones. Cruciferous plants, such as broccoli and cauliflower, and legumes, such as soybeans and clover, and citrus use a lot of molybdenum.
Plant nutrients are either mobile or immobile within a plant. Molybdenum is mobile, which means it moves around easily within a plant. This makes diagnosing deficiencies easier because they are most often seen in older leaves as plants pull nutrients to make new leaves. Molybdenum toxicity is practically unheard of, but deficiencies can be a serious problem.
Symptoms of molybdenum deficiency
Without molybdenum, leaves turn yellow and die and flowers may fail to form at all. The yellowing is often along leaf margins and downward cupping may also appear. In some cases, leaves develop a whiptail shape, rather than the leaf’s normal wider blade shape. Corn kernels may germinate on the cob prematurely in a last-ditch effort at reproduction. Legumes will have fewer or no root nodules if molybdenum is in short supply.
Again, you don’t know what your plants have access to without an inexpensive, lab-based soil test. Take my word for it, it is worth the effort.
Radishes, broccoli, cauliflower, mustards, and other members of the cabbage family produce a special type of seed pod called a silique [se-LEEK] or siliqua [sil-eh-KWA].
What is a pod?
Pods are made from carpels. Carpels are the female reproductive organs of a plant. The pods of legumes are made from a single carpel, while members of the cabbage family produce pods made from two carpels that have been fused. The pods made from fused carpels are called silique.
Pods are a type of dehiscent fruit. Dehiscent means that the structure opens spontaneously when its contents are mature. If a pod does not open automatically, it is called indehiscent. In either case, pods are made up of two identical long halves and they contain seeds. Those halves are the outer walls of the ovary. The two halves are joined along a seam, called a suture. Held between those two halves is a ribbon of seed-bearing tissue called the septum.
There are two categories of Brassica pods: siliqua and silicula. The difference between the two is simply the pod dimensions. If the length of the pod is more than three times the width, it is a silique. If the length is less than three times the width, it is a silicula (or silicle).
If you allow your radishes and other Brassicas to go to seed, you will see siliquae for yourself, plus you will have seeds for next year’s crop!
You’ve probably read dozens of articles and posts about the wonders of dish soap as a pesticide, fungicide, and surfactant in the garden. All of those posts are wrong.
How dish soap works
Dish soap, also known as dish washing liquid, is a detergent. Dish soap helps us get our dishes clean by cutting grease, oil, and wax. Dish soap generally contains colorants, fragrances, bleach, enzymes, phosphates, and rinsing agents.
Insects and plants have waxy coatings that are also damaged by dish soap. When this protective coating is removed, infection, pest infestation, and dehydration all become more likely.
Dish soap v. insecticidal soap
Insecticidal soap is not a detergent. It is a soap made specifically formulated for use on plants. And it must be used properly to be safe for plants and effective against pests. While liquid hand soap is a soap and not a detergent, it contains fatty acids which are phytotoxic, or poisonous, to plants.
Before trying a Quick Fix on your edible plants, take the time to research what is really going on. Your plants will thank you.
Over-fertilization is an increasingly common problem in home gardens.
It happens all the time. Your plants start out doing so well. Then they lose some of their vigor. You might see chlorosis (yellowing), cupping, less fruit production, or simply a failure to thrive. What is a gardener to do?
The traditional response was to add more fertilizer, manure, or aged compost. And it would work. For a while. Then those same symptoms would return, motivating you to add more fertilizer. And more. And more. Until it reaches the point where no matter how much fertilizer you add, your plants are simply not performing well. In fact, they seem more prone to pest infestations and diseases. How can this be?
Balanced plant nutrients
Just as we must eat a balanced diet to stay healthy, plants need access to a balance of nutrients. This is true partly because those nutrients are absorbed at the molecular level, as cations and anions, according to their electrical charge. Too many of one charge or the other makes it difficult for plants to absorb what they need. Also, some minerals, such as iron, are needed to absorb and use other nutrients. If there isn’t enough of these nutrients, or if they are made unavailable due to an imbalance, your plants can starve while sitting at a banquet. Mulder’s chart provides an image of what those nutrient relationships look like.
Too much of a good thing can be a bad thing. In the same way. too much of a nutrient can lead to toxic levels. Phosphorus, for example, is critical to plant growth and photosynthesis and it tends to bind tightly to soil particles. Phosphorus toxicity can lead to severe stunting and it blocks plants from absorbing iron and zinc.
Potassium is critical to enzyme reactions and water and mineral movement within a plant, helps prevent diseases, and regulates the rate of photosynthesis. Potassium toxicity causes leaf distortions, chlorosis, and yellowing along leaf margins. Potassium toxicity can cause calcium, nitrogen, and magnesium deficiencies.
Similar problems occur when there is too much of any nutrient. Compounding the problem, these excess nutrients often leach into rivers, streams, and groundwater, causing algae blooms that kill fish and create ripples of pollution and threats to biodiversity.
Too much of any one nutrient can throw a monkey wrench in the works. Too much of several nutrients can take years to resolve.
Is your soil over-fertilized?
The first step it to get a soil test. You don’t know what is in your soil without a soil test from a reputable lab. Sadly, those colorful over-the-counter soil tests are not accurate enough (yet) to be really useful. Many universities offer inexpensive soil tests. These tests can save you time and money and help your plants be healthier.
Below, you can see my soil tests from 2015 and 2019. In 2015, I learned that the property we bought had been over-fertilized for a very long time. Phosphorus and magnesium levels were critically high, and there was too much of pretty much everything. Except iron.
Remember what I said about iron and nutrient absorption? Yep, my plants had been sitting at a feast, unable to do more than nibble. And it showed. The plants in my landscape were prone to fungal disease, borers and other insects, and they simply were not thriving.
For four years, I thought I was doing better. I added a little iron. I avoided using any fertilizer, besides blood meal and ammonium sulfate (for nitrogen). But I continued to add aged compost to help reduce my compacted soil. My compost is mostly made up of chicken coop bedding. It ends up that chicken poop contains very high levels of nitrogen, potassium, phosphorus and calcium. While my plants needed the nitrogen, they certainly didn’t need any of the other nutrients.
How to correct over-fertilization
Looking at the results of my 2019 soil test, I realized that I hadn’t done nearly enough to correct my over-fertilization problem and had wasted 4 years in the process. Now, to correct the problem, I have stopped using my nutrient-rich compost on the ground. Instead, I am saving it for raised beds and container plants until my over-fertilization problem has been corrected.
And that’’s the cure - stop adding nutrients. The other half of the cure for over-fertilization is to remove nutrients by taking plant material out of your yard completely. Instead of grasscycling, bag and remove grass clippings. Or, you can add them to the compost pile or feed them to your chickens. Avoid using the chop and drop method for a while. Plant more heavy feeders, such as asparagus, beans, beets, broccoli, Brussels sprouts, cabbage, carrots, celery, corn, cucumbers, eggplant, garlic, leeks, melons, okra, onions, parsnips, peas, peppers, potatoes, pumpkins, shallots, squash, tomatoes, and turnips. And harvest those crops to within an inch of their lives. Take everything they have to give and get it out of your yard.
Armed with the results from my more recent soil test, I am now adding far more iron, to help my plants absorb what they need, and using wood chip mulch to counteract the compacted soil, but these actions will take time to have an effect. To monitor the effectiveness of these new actions, applying more iron and removing more plant material, I will switch to annual soil tests until the over-fertilization problem has been resolved.
I urge you to do the same.
Conifers produce seeds but not flowers. This makes them gymnosperms. Instead of flowers, conifers produce cones. Botanically known as strobili, cones are the reproductive organs of conifers.
There are male cones and female cones. Male cones, called microstrobilus or pollen cones, produce pollen and look very little like the cones we imagine. Male cones are more herbaceous than female cones and they look very similar to one another across species. Female cones are the familiar woody structures that produce and contain seeds. Female cones, also known as seed cones, ovulate cones, and megastrobili, are structurally unique to each species and helpful when it comes to identification.
Female cones are covered with plates called scales. Female cones start out as a central stem covered with bracts. Bracts are modified leaves or scales with a small flower or flower clusters in its axil. The bright red “petals” of poinsettia are not actually flowers. They are bracts. In some cases, the bracts harden and fuse to the woody seed scales.
Male cones appear in clusters and are much smaller than female cones. They contain pollen sacs and generally start growing on the end of the previous year’s branches, usually lower in the tree canopy, below female cones. This prevents self-pollination.
Cone and seed development
While male cones usually only last one year, it can take 3 or more years for a female cone to fully develop. Once a female cone is receptive and pollination has occurred, it can take up to a year for fertilization to be complete. As seeds develop, some cones will slowly begin to open, while other species need fire to trigger opening. Stone pine seeds, while delicious, require a lot of hard work to separate them from their cones.
Some conifer seeds have a wing that allows them to be carried on the wind, while other species rely on animals, such as squirrels, and birds help them disperse. Stone pine seeds, while delicious, require a lot of hard work to separate them from their cones.
Types of cones
The cones of holiday decoration fame are only one of many different types of cones. The scales can be arranged in one of two ways: imbricate or peltate. Imbricate scales overlap much like roof tiles and are attached along a common axis. Peltate scales do not overlap and are attached from a central point, more like an umbrella. Some cones look more like berries than cones.
Araucariaceae (monkey-puzzle tree, kauri, and the nearly extinct Wollemia tree) - fused scales create a spherical cone; imbricate
Cupressaceae (arborvitae, cypress, juniper, redwood, sequoia) - bracts and seed scales are fused; peltate
Pinaceae (cedar, fir, larch, pine, spruce) - archetypical cone; imbricate
Podocarpaceae (Prince Albert’s yew, Matai) - many of the scales are fused into a brightly colored, often edible aril; imbricate
Sciadopityaceae (Japanese umbrella pine) - imbricate
Taxaceae (yew) and Cephalotaxaceae (plum yews) - female cones have only one scale, with a single poisonous ovule; the surrounding fruit is sweet but the seed is deadly
While not conifers, cycads and welwitschia, or tree tumbo, also produce cones. Tree tumbo plants are considered living fossils and are unique in that female plants produce female cones and male plants produce male cones.
How many cone-producing plants do you have?
Plants are particularly thin-skinned. Did you know that a plant’s epidermis is only one cell thick? Just under that skimpy outer layer is a plant’s cortex.
The cortex is made up of thin-walled cells called parenchyma. Some of those cells are purposefully torn or separated to create air spaces. This porous tissue is called the aerenchyma [a-REN-ky-ma], from the Greek word for ‘infusion’. This word makes sense when you learn that the phloem is not the only part of a plant that transports nutrients. The cortex does, too!
The cortex is responsible for transporting nutrients and carbohydrates into the central core of a plant’s roots through diffusion. But there is even more to the cortex than just nutrient transportation.
Functions of the cortex
Depending on the plant, cortical cells may also store carbohydrates, essential oils, latex, resins, and tannins. in many cases, the cortex also contains chloroplasts that are able to perform photosynthesis, converting carbon dioxide and water into simple carbohydrates. Taking things one step further, the cortex can then convert those simple carbohydrates into the complex carbohydrates found in bulbs, tubers, and root vegetables, such as beets, carrots, and turnips. The cortex also manufactures the bark seen on the outside of woody plants and the underlying cork.
Cortex and water flow
In herbaceous plants, the innermost layer of the cortex is called the endodermis and the outermost layer is called the exodermis. The endodermis and exodermis are unique in that all of the cell walls have a woody band, called the casparian strip, except those facing the center or the outside of the plant. These casparian cells help regulate the flow of water between the vascular bundles, found just inside the cortex, and the outer cells of the cortex and epidermis.
Flax stem cross-section: 1. Pith 2. Protoxylem; 3. Xylem; 4. Phloem 5. Bast fiber 6. Cortex 7. Epidermis (Public Domain)
Pests and diseases of the cortex
Several bacterial diseases invade the root cortex through injury sites and natural openings. These diseases include bacterial wilt of beans (Curtobacterium), ring rot of potatoes (Clavibacter), cucurbit bacterial wilt (Erwinia), black rot of cucurbits (Xanthomonas), and Pierce’s disease of grapes (Xyella). The Pythium oomycete, which causes blackleg, also moves through the cortex. Dry, brown lesions seen in the main or taproot cortex can indicate Fusarium crown and root rot.
The next time you cut a plant stem or root, use a magnifying glass or hand lens to see what’s really going on in there. There are some amazing things going on in there!
Cavitation is the sound of water breaking.
While we don’t normally think of water being able to “break”, the columns of water that move upward through a tree’s veins can be broken, allowing air bubbles to form or simply severing a pathway for life-giving water.
Trees use a lot of water
The general rule of thumb for how much water a tree needs each week of summer is 10 gallons of water for every inch of trunk diameter, as measured at knee height. This means a large, mature tree, with a trunk diameter of 18”, will need 180 gallons of water every week at the peak of summer, on average. The flow of that water is critical to a tree’s health.
In healthy trees, water is absorbed through the roots and pulled upward through tubes called xylem. There are thousands of xylem in a mature tree. Picture the xylem as straws that run the vertical length of a tree. Water moves through xylem in a process called transpiration.
Transpiration refers to the way negative pressure is created within xylem as water evaporates from the surface of the leaves. This occurs because of surface tension, or the tendency of water molecules to stick together. When one water molecule leaves the plant through evaporation, lower water molecules are pulled upward.
Bubbles can be bad
Bubbles might be fun to play with, but bubbles in veins are bad. Just as air bubbles in an IV tube can kill you, so, too, can bubbles block the flow of life-giving water for a tree. Rapid transpiration can cause air bubbles to form in xylem. If too many air bubbles remain in place, it can kill a tree. Cavitation is much like an embolism for trees. Small, infrequent bubbles are not a serious problem. Large, fixed bubbles are deadly.
During periods of drought, the rate of evaporation on the surface of the leaves is so great that xylem can collapse and break, like a rope pulled too tautly. These breaks halt the flow of water completely, also killing a tree. Cavitation also occurs in response to thawing after water within a tree has frozen.
The sound of silence
If you could hear higher frequencies, it would sound similar to popcorn popping. In most cases, the frequency of this sound is too high for us to hear, but it can, occasionally, be heard. [It might be fun to try using a stethoscope on a tree…] I can only imagine that our peaceful summer walks in the woods sound more like a riot of trees screaming for water to our dogs…
Bottom line: make sure you irrigate your trees properly to keep them healthy, especially during summer.
Sometimes plants grow in ways you might not expect.
Instead of a nice round stem or flower, you get a flattened ribbon shape, or undulating folds, called ‘cockscomb’. This is called fasciation. It is also known as cresting.
Fasciation is a relatively rare physiological disorder that can create some really beautiful mutations. It can occur anywhere on a plant, but stems and flowers are the most commonly seen examples.
How does fasciation occur?
In normal plant development, growing tips (apical meristems) focus all their resources on a single point. This is what gives us straight and/or cylindrical stems and flowers. Fasciation elongates the apical meristem, creating a ribbon-like growth. The Latin word fascia means “a band” and can refer to anything that looks like a ribbon or wide band.
In some cases, these distortions can create unique bends, twists, and odd angles, or unusual clusters of growth that look like a witches broom. Flowers and leaves growing on these distorted stems may be smaller than normal, more abundant, or have other unique characteristics of their own.
One rare form of fasciation, called ring fasciation, has a ring-shaped growing point that creates hollow tubes.
What causes fasciation?
Fasciation can be caused by plant hormone imbalances, genetic mutations, environmental conditions, or bacterial, fungal, or viral infections. It can also occur for no apparent reason. Environmental factors include chemical overspray or exposure, mite or other insect infestation, and the presence of certain fungi. Exposure to cold and frost can also cause fasciation. Unless the fasciation is caused by bacteria, it is not contagious to nearby plants.
Plants affected by fasciation
In addition to my milkweed, this condition is most commonly seen on nasturtiums, geraniums, dandelions, and ferns. It has also been seen on fruits and vegetables, such as asparagus and broccoli.
Some plants are prized and propagated simply because of their fasciation. I look at it as a nice little surprise from the garden.
Have you seen fasciation in your garden?
Long, long ago, there were no flowers.
It wasn’t until the Cretaceous period, some 130 million years ago, that a handful of renegade cone-bearing gymnosperms started protecting their naked seeds with a new structure. This new, flimsy bit of color was so successful at boosting pollination rates that it spread far and wide, making flowering plants (angiosperms) one of the most successful types of plant life on Earth.
That structure is the petal.
Of course, that’s a pretty big claim for such a delicate flap of plant tissue. Too frequently discounted as an unimportant fashion accessory to more vital, functional parts of plant anatomy, there is far more to a flower petal than meets the eye!
Before we get to the really astounding stuff, let’s make sure we know what we are talking about when we talk about petals.
What are petals?
You may be surprised to learn that petals are modified leaves. In fact, sepals, stamens, and carpels are all genetic twists on the leaf. As a modified leaf, a petal has a broad, flat area called a blade. At the narrow end, where the petal attaches to the plant, is the claw, which is very similar to a petiole, or leaf stem. Where petals are attached to one another is called the limb. The petals that make up a flower are called its corolla.
Just under a collection of petals is another set of modified leaves, called sepals. Sepals are usually green. When discussing the combined petals and sepals of a flower, it is called the perianth. When sepals and petals are indistinguishable from one another, they are called tepals. [Aloes and tulips are tepals.] Sometimes, sepals look more like petals than leaves. When that occurs, they are said to be petaloid.
Petals of parentage
The number of petals present in a flower, the way the petals are arranged, whether or not they are fused to neighboring petals, or how much they are fused, as well as color are used by pollinators to find the pollen and nectar they seek. We can use the same information to identify unknown plants
First, flowers with 3 or 6 petals tend to be monocots, while flowers with 4 or 5 petals, or groups thereof, are most often eudicots, though not always. Petal arrangement, or floral symmetry, can also help with plant identification:
Petals, in particular, evolved to protect the reproductive part of a flower and to attract or repel specific pollinators. We know that flowers come in every color imaginable, but did you know that they also feature colors we cannot see, with glowing flight lines, traffic patterns, and welcome mats? It’s true! Flowers exist to attract the type of pollinator that will help them to procreate their species. Not all pollinators are created equally. It is a waste of resources for a plant (or any living thing) to attract the wrong sort.
The story of floral scent
Orchids produce floral scent in specialized sacs, but most flowers get their scent from chemicals produced by the petals. While many of us, along with most insect and bat pollinators, find floral aromas appealing, herbivores and disease-carrying insects often disagree with that evaluation. Combined with the colors, petal arrangement, and floral placement, floral scent works to increase a flower’s chance at becoming pollinated and/or fertilized.
Did you know that plants use floral scent to communicate with each other? It’s true! The volatile chemicals that give a flower its fragrance trigger a behavioral response in a surprising number of neighboring life forms and no two floral scents are identical, sort of like snowflakes.
Sensing a reproductively fertile neighbor, another flower may shift its chemical production to attract pollinators of its own. On the other hand, a fertilized flower will often release ethylene, a ripening agent, to discontinue the scent so that local pollinators will turn their attentions to neighboring flowers in need of pollinating. Also, injured flowers produce different scents than those being chewed on by herbivores. We can’t see it or smell it, but it’s going on all the time.
The Daily Garden is all about plant vocabulary. Today, we are looking at overall plant anatomy because it can be difficult to talk about something if you don’t know the words.
By taking a closer look at plant anatomy, we will be better able to understand each other, we can get more out of plant descriptions, and be better able to identify those mystery plants that always seem to pop up in the yard.
Plant anatomy, or phytotomy, starts with simple descriptions of the outside and inside of plants. Remember those black-line masters from grade school used to teach parts of a plant? Well, let’s start there.
Basic plant systems
Plants are have two basic systems: roots and shoots, with the root system below ground and the shoot system above ground. Roots provide anchorage and often store nutrients. Roots can develop as a taproot or fibrous root system. Roots have hairs that absorb water and nutrients. The shoot system consists of vegetative parts (leaves and stems) and reproductive parts (buds, fruits, seeds, and flowers or cones). Let’s take a closer look at each of those parts.
Leaves are the sugar factories of the plant world, absorbing sunlight and converting it into sugar through photosynthesis. The wide, flat part of a leaf is called the blade, or lamina. The shape of the leaf blade is very useful in plant identification, as is the way those leaves are arranged along a stem and the pattern of veins within a leaf. The edge of the leaf is called its margin. Leaves are coated with a waxy protective cuticle. There are tiny holes, usually found on the underside of a leaf, called stoma, that allow plants to exchange gases with the environment and to regulate water flow within the plant. The stem that connects a leaf to a stem is the petiole. Leaflike structures seen at the base of the petiole are called stipules,
Stems support leaves, flowers and buds. These structures are attached at nodes. The spaces between nodes are called internodes. Herbaceous stems have waxy cuticles for protection while woody plants have bark. Stems contain a vascular system that consists of the xylem, phloem and may include a cambium layer. This system carries food, water, and minerals throughout the plant. That vascular system is arranged in a circular pattern in dicots and eudicots, while it is more scattered in monocots. Twigs are woody stems from the previous year. Branches are more than one year old and may have lateral stems. Trunks are the main stem of woody plants, such as trees and shrubs. Canes are a type of stem filled with spongy pith. Canes generally only live for a year or two. Modified stems occur both above and below ground. Bulbs, corms, rhizomes, and tubers, such as potatoes, are below ground modified stems. Crowns, spurs, and stolons are aboveground modified stems. Thorns are also modified stems, but rose thorns are not really thorns. They are prickles, which are modified epidural, or skin cells. Stubby stems, called spurs, produce fruit buds.
Buds are shoots that may develop into leaves or flowers. Buds are identified by their location on a stem: lateral buds are found along the sides of a stem, while terminal buds are found at the end. Lateral buds usually grow where leaves meet the stem and are called axillary buds. Renegade adventitious buds may show up at injury sites, on roots, or even at the edge of a leaf. The place where buds fall off leave a mark called a bud scar. Tree leaf buds have scales, while leaf buds of annuals and herbaceous perennials have delicate naked buds. Potato eyes are clusters of buds.
Fruits are ripened plant ovaries. Fruits can be simple (formed with one ovary), as in the case of stone fruits, or compound (formed with several fused ovaries). Compound fruits can be multiple or aggregate. Apples and other pomes are multiple compound fruits. You can tell by the 5-pointed star shape in the center of the fruit. Raspberries, which are drupes, not berries, along with pineapples and figs are formed by many flowers fusing together and are called aggregate fruits. By the way, strawberries are not berries, either. They are ripened receptacles. Berries, such as pumpkins, cantaloupes, cucumbers, eggplants, and tomatoes, all have many seeds inside an outer shell of varying thicknesses and hardnesses. Dry fruits, such as peas and beans, grow in pods that either open down a seam (dehiscent), or stay closed (indehiscent), as in the case of peanuts and most cereal grains, such as wheat and barley.
Seeds have three parts: the embryonic plant, stored food, called endosperm, and a protective seed coat. As temperatures rise and moisture is absorbed through the sed coat, a primary root, called the radicle, will emerge, followed by the first stem, or hypocotyl. First leaves, or cotyledons often look very different from adult leaves.
Flowers exist solely to attract pollinators. Only angiosperms make flowers. Gymnosperms, such as conifers, ginkgo trees, and cycads make cones, or strobili. The colors, patterns, showy displays, and sweet aromas we associate with flowers are all in place to attract insects, bats, and birds. Flowers are supported by a stem called a peduncle. Small green leaf-like structure, called sepals, are often seen at the base of a flower. A collection of sepals is called a calyx. Individual petals may produce nectar or scent. All of the petals together are called the corolla. The combined corolla and calyx are called the perianth. The tip of a flower stalk, called the receptacle, contains the plant’s reproductive organs. Flowers can be male, female, or both, though not always at the same time. The female part, or pistil, consists of a pollen-receiving stigma, supportive style, and the ovary. [When you eat saffron, you are eating the style and stigma of an autumn crocus flower.] The male part, or stamen, consists of a pollen-producing anther and a supporting filament. Flowers are very useful in plant identification.
Genetic research and electron microscopes have brought plant anatomy to exciting new levels. Assumptions about kinship have been wrecked asunder and colorized scanning electron microscope (SEM) images can be breathtaking. Different types of plant cells gather together to create tissues. Those tissues come together to create the functional parts of a plant.
Ultimately, all those functional parts grow into delicious, nutritious foods that we can cultivate in our yards for decades. For me, feet up in the yard with a nice glass of wine beats standing in line at a grocery store any day!
What do wedges of citrus, hard walnut shells, the white bits inside a pomegranate, and the paper coating around avocado pits have in common?
They are all endocarps.
How can this be? How can structures so very different be the same part? Let’s find out by starting with some basic fruit facts.
The fruits and seeds we eat are plant ovaries. When a flower is pollinated and fertilized, three new structures form: seeds, pericarp, and placentae. Embryonic seeds attach to the placenta, and pericarp begins to grow, to feed and protect the embryonic seed, and to attract seed-spreading herbivores. There are three different types of pericarp tissue: exocarp (outer skin), mesocarp (flesh), and endocarp (inner layer). So, endocarp is the interior fruit that surrounds seeds. But what about all those differences?
Types of endocarp
Endocarp is generally not fruit in the way you would expect, unless you are talking about peppers or citrus. The fleshy parts of sweet peppers and chili peppers is the endocarp, as are those membranous wedges of fruity goodness found inside lemons, limes, and oranges. If you look inside an apple, the endocarp is the hard clear plate-shaped bits close to the seeds.
If you take a close look at a stone fruit, such as a nectarine or cherry, the endocarp is very hard and inedible. To us, it looks more like the shell of a nut. And guess what? The hard outer shell of walnuts, pecans, and almonds, that shell is the endocarp, even though, to us, it looks as though it is on the outside.
Confused? Read on!
Nuts about endocarp
When a nut develops on a tree, the exterior rarely looks like what you see in the grocery store. Many nut species have smooth or furry green exteriors (exocarp). That exocarp coats a hard, familiar shell. That shell is the endocarp of a nut.
Stamens are the male aspect of a flower.
Flowering plants, or angiosperms, have flowers that can be male, female, or both, though not usually at the same time.
The word stamen comes to us from the Latin word for ‘thread’. This is because the stamen is a threadlike stalk, called a filament, which has a pollen-producing anther on top. The stamen usually surrounds the female part, or pistil, though not always
Different plant families have different arrangements of pistils and stamens. For example:
When eating edible flowers, it is a good idea to remove the stamen and pistils and just eat the petals and other parts. The only exceptions are violas and Johnny-jump-ups. In these cases, the other parts add good flavor. Saffron threads are the dried [female] styles and stigmas of a specific crocus flower species, not the stamen.
Melons, zucchini and other squashes can easily be hand-pollinated by breaking off a pollen-carrying stamen and touching each of the flowers flowers with it.
Now you know.
You’ve heard of tannins, but what are they?
The word tannin comes to us from Medieval Latin and it refers to oak bark. Oak, chestnut, and other tanbarks were used in tanning leather. Now, I do not mean some cow slathered itself with cocoa butter and lounged on the beach. Hardly. The process of tanning a raw animal skin and converting it into durable leather requires a lot of hard work and some powerful chemicals.
Tannins are large acidic molecules that bind to and alter proteins, which is why they were used in tanning leather. Tannins also bind to starches, minerals, and cellulose. This binding action slows decomposition. You may have seen ponds in forest environments with brownish water. That brown color is likely caused by tannins leaching out of nearby plants and into the water. In the plant world, tannins are used as pesticides, to protect against predators, and to regulate growth.
Plants produce tannins to make themselves less palatable and harder to digest. This discourages feeding by some herbivores. To counteract the presence of those tannins, some plant eaters have evolved to include a tannin-binding protein in their saliva. [Isn’t the world amazing?] The latex produced by dandelions contains tannins.
Tannins as growth regulators
Tannins also have antimicrobial and allelopathic actions. Allelopathy is a type of plant chemical warfare in which one plants releases chemicals that inhibit the growth of neighboring plants. This growth regulation can occur by reducing the available nitrogen or oxygen in the soil, killing nearby beneficial soil microorganisms that support plant life.
If you bite into an unripe fruit, it is the tannins that cause your mouth to pucker. As fruits approach maturity, the level of tannins decreases. Many popular garden plants contain tannins, to one degree or another, including:
In autumn, when leaves turn color, the golds and yellows you see are the result of tannins.
Now you know.
Botanical stigmata are part of the female reproductive system.
Tiny stigmata may not grab your attention at first glance, but maybe they should.
Before we learn why, let’s do a quick review of flower anatomy.
Stigmas and pollination
Carried by insects, bats, or wind, pollen is received at the stigma by sticky, specialized cells (stigmatic papillae). Once the pollen has been captured, the stigma, which is often quite moist, helps to rehydrate the pollen after its lengthy travels. Once hydrated, the pollen grain germinates, sending a pollen tube down the style to the ovary. To ensure that the proper pollen is collected, stigmas have evolved some very fancy attraction and capture methods.
You may be surprised to learn, as I was, that high temperatures, usually above 104°F, for 2 or more days prior to pollination, can exhaust the stigma of tomato plants to the point they cannot capture pollen. This may explain why, during particularly hot summers, we see lots of tomato blossoms, but no fruit. High temperatures (above 100°F) also reduces pollen germination.
Besides being sticky, stigmas use various shapes, flaps, and hair arrangements to help ensure that the correct pollen is captured and all others are rejected. These shapes can be simple tubes, truncated tubes, threadlike, bulbous, conical, lobed, feathery, hairy, beaked, fan-shaped, brush-like, leaflike, or disc-shaped. The familiar threads found on ears of corn, called silk, are stigmata.
How many different stigmata shapes are there in your garden?
When you cut flowers for a bouquet, you are generally cutting the peduncle. Peduncles are simply flowering stems, but they may surprise you.
Peduncles can occur in plants without stems, they may continue to grow indefinitely, and some peduncles grow underground.
The peduncle of a simple flower is easy to recognize. It is the classic stem you hold, cut, or put into a vase to admire. Its job is to support the flower. An artichoke stem is a peduncle, and for the same reason.
Now you know.
A flower is a flower, unless it is a bunch of flowers growing on the same stem, then it’s an inflorescence.
Anatomy of an inflorescence
A singular flower appears at the end of a stem, called a peduncle, nestled in a (normally) green cup, called the receptacle, and surrounded by modified leaves, called sepals. When there are multiple stems or branching stems (rachis), or flowers that occur on a disk, it is an inflorescence. The stalks of individual flowers within an inflorescence are called pedicels. These flowers are called florets, and their leaves are called bracts.
Types of inflorescences
Inflorescences can be determinate or indeterminate. The oldest flowers of a determinate (cymose) inflorescence are found at the end of the stem, as other flowers bloom in succession, down the stem, with the youngest flowers at the base. Indeterminate inflorescences are just the opposite, with older flowers at the base and younger flowers occurring closer to the tip.
There are also catkins (mulberry), spadix (cobra plant), and many subdivisions of each category, but this is a good start.
When an inflorescence produces fruit, such as sunflower seeds, it is called an infructescence.
Now you know.
We’ve all heard of a “hill of beans”, but did you know that beans have hilums?
Beans, peas, and other legumes produce fruits, called pulses, in pods. If you look closely, you can see where the seed attaches to the pod. Once the fruit or seed is mature, the pod opens along a seam, which means they are dehiscent. After the pod opens, the seeds fall to the ground where they are protected by a hard, water-resistant seed coat.
Seed coats have scars. When the seed separates from its pod, one scar is formed. This scar is called the hilum. On beans, the hilum is called the “eye”. Another scar, called the raphe, is a seed’s bellybutton. This is the scar that forms when the seed was separated from its placenta, within the pod. If you look even closer, you can see a tiny opening, called the micropyle, at one end of the hilum. This opening is where water is absorbed to allow germination to occur.
Chestnuts have hilums, too.
Now you know.
You can grow a surprising amount of food in your own yard. Ask me how!