plant anatomy

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Tea Time: Self-heal

Prunella vulgaris can be found all over the place. It has also been used to treat just about everything. What else would you expect from a plant known commonly as self-heal, heal-all, all-heal, and woundwort? The medicinal value of this plant has been appreciated for centuries across its expansive range, and studies evaluating its medicinal use continue today. Being such a ubiquitous species – both as a garden plant and a native plant (and also a common weed) – and because it has so much clout in the world of herbal medicine, it’s an obvious candidate for Tea Time.

Self-heal is a member of the mint family (Lamiaceae), easily distinguished by its square stems, opposite leaves, and bilabiate and bilaterally symmetrical (or zygomorphic) flowers. One surprise is that, unlike the many aromatic members of this family, the foliage of self-heal lacks a strong scent. P. vulgaris occurs naturally across Asia, throughout Europe, and in parts of northern Africa. It is also widely distributed across North America. Apart from that, it has been introduced to many regions in the southern hemisphere and has also been frequently moved around throughout its native range. Eurasian varieties now intermingle with North American varieties, which can make it difficult to determine a native individual from an introduced one.

self-heal (Prunella vulgaris)

Self-heal is an adaptable plant that tends to prefer shady, moist locations, but can also be found in open, dry, sunny sites. Find it along forest edges, roadsides, ditches, and trails, as well as on the banks of streams, lakes, and reservoirs. It occurs in gardens, both intentionally planted and as a weed, and can escape into lawns, vacant lots, and open fields, as well as into nearby natural areas.

P. vulgaris is an evergreen that grows both prostrate and upright, sometimes reaching 1 foot tall or more (but is often much shorter). It has shallow, fibrous roots, and its stems root adventitiously as they sprawl across the ground, frequently forming an extensive mat or groundcover. Its leaves are oval to lance-shaped and measure about one inch long. Lower leaves have petioles, while upper leaves may become stalkless. Leaf margins are entire or can be slightly toothed. As plants age, they can develop a coppery or purple-bronze color.

the leaves of self-heal

The flowers of self-heal are generally a shade of purple, but can also be white, pink, or blue. They bloom irregularly in a spike measuring up to two inches long. Flower spikes are thick, dense, cylindrical, and made up of whorls of sharp-pointed bracts. Flowers bloom irregularly along the spike and occur from late spring/early summer into the fall. Each flower produces four nutlets, which sit within a cup-shaped, purple calyx.

As a medicinal herb, self-heal has been used both internally and externally to treat a long list of ailments. These include sore throats, diarrhea, fevers, intestinal infections, liver problems, migraines, heart issues, dermatitis, goiter, and thyroid disfunction, just to name a few. It has been used topically to treat skin irritations, bites, stings, and minor cuts and scrapes. This is thanks to its antimicrobial properties and its ability to stop bleeding. A report in the journal Pharmaceuticals (2023) calls P. vulgaris an “important medicinal plant” due to its “rich chemical composition” and its “pharmacological action.” Chemical analyses find the plant to be a valuable source of phenolic compounds, flavonoids, rosmarinic acid, and ursolic acid, among numerous other compounds. If you are curious to learn more detailed information regarding this plant’s medicinal value, you can refer to the above report, as well as one found in Frontiers in Pharmacology (2022).

self-heal tea

P. vulgaris is an edible plant, and its young leaves can be eaten raw or cooked. The leaves together with the flowers can also be dried and used to make a tea. This is how I had it. I used about two teaspoons of dried leaves to one cup of water. Feel free to use more if you would like. I thought the tea was pretty mild. It had a slight sweetness to it and a hint of mint flavor. It has been described as bitter, but I didn’t find it to be overly so (although I may have a higher tolerance for bitterness). Sierra tried it and said that it tasted like “water left over from something else.” That might be because it was more diluted than she would have preferred. Overall, I thought it was a pleasant experience and would be happy to drink it again.

More Tea Time Posts on Awkward Botany:

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Garden Plants Gone Wild: The Periwinkles

In a garden setting, a successful groundcover is a plant that is durable and adaptable, spreads readily, and fills in space thouroughly. The point of planting a groundcover is to cover exposed soil and create a sort of living mulch. In fact, groundcovers provide similar benefits to mulch. They prevent erosion, help retain soil moisture, and prevent weeds. It should come as no surprise then, that a plant that fulfills all of these requirements has the potential to become a weed, especially if given the opportunity to escape and establish itself outside of its intended location.

This isn’t a hypothetical. This exact scenario has played out numerous times. A good example of this are the periwinkles: Vinca major and Vinca minor. Both have been popular garden plants for centuries. Their introduction to U.S. gardens came as early as the 1700’s. Today, both species (including cultivars of each) can be found for sale in nurseries throughout the country, even while escaped periwinkles proceed to spread across natural areas and uncultivated spaces. Even in gardens where periwinkles have been intentionally planted, they can be deemed no longer welcome due to their aggressive nature. Eliminating them, however, is a formidable task.

greater periwinkle (Vinca major)

Periwinkles are relatively easy to identify, yet telling the two apart can sometimes pose a challenge. Knowing what to look for can make this a fairly simple task. Vinca major (greater periwinkle) is the larger of the two. Its stems are tough and sprawl up to 5 feet long, rooting adventitiously when in contact with the ground. Vegetative spread also occurs via stolons and rhizomes, modified stems that spread horizontally both above and below ground and whose main purpose is to produce new roots along their length. This extensive rooting creates dense mats of stems and foliage, precisely what you’d want from an effective groundcover. Leaves are arranged oppositely and are semi-evergreen with fine hairs along their margins. They are thick, glossy, simple, dark green, and ovate to ovate-lanceolate in shape. They have a relatively long petiole, and some leaves can even appear heart-shaped.

The flowers of V. major are blue to purple and fused at the base to form a tube, separating into five distinct lobes and creating a shape similar to a pinwheel. They are borne on a long stalk in the axils of leaves and measure about two inches wide. Their sepals are long, slender, pointed, and lined with bristly hairs. Fruits rarely form, but when they do, they are narrow follicles.

comparing the petals and sepals of Vinca major (left) and Vinca minor (right)

Vinca minor (lesser periwinkle) is a slightly smaller plant with a similar habit, spreading vegetatively in all the same ways as V. major. Stems are slender and smooth and leaves are evergreen. Compared to V. major, the leaves of V. minor are smaller, narrower, and have hairless margins and short petioles, otherwise they are very similar. Same goes for the flowers, which look identical on both species, except that those of V. minor are slightly smaller (about one inch wide) and borne on shorter stalks. Sepals are shorter, broader, more rounded at the tips, and lack the bristly hairs of V. major.

Because periwinkles only rarely produce seed, their main method of getting around is vegetatively. Fragments of roots or rhizomes hide in soil and are moved from one location to another inadvertently. Periwinkles are often used in hanging baskets and containers, and when these things are cast aside at the end of a season, the perennial roots of periwinkles may continue to grow, spreading out beyond the potting mix and into the soil.

Dump soil, yard waste, and improperly disposed of containers are the main ways that periwinkles find their way into natural areas. Both species can be found in the understories and edge habitats of woodlands, as well as along roadsides and pathways, and in vacant lots and old homesites. They can also be found in riparian areas, where waterways can carry fragments of plants to new locations. The Invasive Plant Atlas compiles reports of both V. major and V. minor growing outside of cultivation and tracks them on a map. They also track which states include them in noxious weeds lists or laws.

lesser periwinkle (Vinca minor)

The best way to keep periwinkles from continuing to spread outside of cultivation is to refrain from growing them. If you choose to have them in your yard, dispose of plant parts properly. If you keep them in containers, send those containers to the landfill when you are done with them. If your property is adjacent to natural areas, the risk may be too great and you may want to consider a different groundcover. Depending on where you live, alternatives vary. In the Intermountain West, potential substitutes include wild strawberry (Fragaria virginiana), woodland strawberry (F. vesca), kinnikinnik (Arctostaphylos uva-ursi), and wild ginger (Asarum caudatum). Each of these are low growing, evergreen to semi-evergreen, spreading plants that do well in shade and can handle some degree of drought.

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Randomly Selected Botanical Terms: Phyllaries

Flowers in the aster family have one of the most recognizable shapes in botany – a circle with a series of petals surrounding it. If you were asked to draw a flower, there is a good chance your drawing would look something like a sunflower, a daisy, a cosmos, or an aster. It’s one of the most basic flower shapes, and yet it isn’t a single flower; it’s a pseudanthium – a false flower. This is because what might appear as a single flower is actually a collection of tens, hundreds, or even thousands of tiny flowers. This aggregation of flowers into a single compact unit is the reason the family was once given the name Compositae, and even now is often informally referred to as the composites.

Another reason why a flower in the aster family – or Asteraceae – might be the first thing you would draw is because it is the largest family of flowering plants, numbering up to 33,000 species worldwide. Chances are you’ve seen a few of them around. In the contiguous U.S. alone, there are more than 2400 species, and that doesn’t include the plethora of species brought in from regions across the world either intentionally (to be grown in our gardens) or unintentionally (as weeds). Of course, not all of the species in this family are going to have a typical sunflower-like flower head, but they do all have a specific type of inflorescence called a capitulum. Capitula are made up of densely packed, miniature flowers called florets, which are stalkless (or sessile) and arranged on a flattened central stem (or axis). There are at least four different types of florets in the aster family, but we’ll leave that discussion for another time.

In this post, we’re specifically interested in what is happening at the base or underside of the capitulum. All of the florets in a capitulum are held within a cup or bowl-shaped series of bracts called an involucre. Bracts are modified leaves, and this whorl of tightly held or loosely arranged bracts are initially found surrounding a developing flower bud. As the inflorescence opens, the involucre opens as well and its bracts persist at the base of the flower head. The bracts that make up the involucre are called phyllaries, and they vary in shape, number, and size depending on plant species. In fact, the features of phyllaries are so unique they are often relied on to help identify a plant in the aster family to genus, species, and infraspecies (variety, subspecies, etc.).

phyllaries of blanketflower (Gaillardia aristata)

When it comes to flowers in the aster family, there is more than meets the eye. After you take some time to appreciate the intricate beauty of its collection of florets, turn the flower head over and take in its phyllaries. They come in various colors, they can be hairy or smooth, their margins can be entire or adorned with hairs, teeth, etc., they can be flat and straight or they can curve outwards in interesting ways, their tips can be pointed, spine-tipped, rounded, or keel shaped. Phyllaries can be laid out very evenly, tightly overlapping each other like shingles on a roof (i.e. imbricate) or their arrangement can be slightly uneven and irregular (i.e. subimbricate). Use a hand lens to get a closer look at all of these features. As you get in the habit of observing the details of the involucre and its phyllaries, chances are each time you come across a flower in the aster family, you’ll find yourself flipping it over to get a look at its undercarriage. What will you find?

phyllaries of dandelion (Taraxacum officinale)
phyllaries of Mexican sunflower (Tithonia rotundifolia)
phyllaries of stemless four-nerve daisy (Tetraneuris acaulis)
phyllaries of hoary tansyaster (Dieteria canescens)
phyllaries of aromatic aster (Symphyotrichum oblongifolium ‘October Skies’)
phyllaries of curlycup gumweed (Grindelia squarrosa)

If phyllaries have piqued your interest and you’d like to learn more about plants in the family Asteraceae, I highly recommend getting your hands on the book, The Sunflower Family by Richard Spellenberg and Naida Zucker. It has a North American focus, but it’s a great place to start learning more about this massive plant family.

More Randomly Selected Botanical Terms:

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Another Year of Pollination: Viscin Threads

While we’re on the subject of pollen-gluing mechanisms, there is another material apart from pollenkitt that a limited number of flowering plant families use to link their pollen grains together. It functions, much like pollenkitt, by aiding in the attachment of pollen to visiting animals. However, unlike pollenkitt, it isn’t sticky, oily, or viscous, and is instead more like a series of threads. Viscin threads to be exact.

One of the major differences between pollenkitt and viscin threads is their composition. The lipid-rich coating that surrounds pollen grains, which we call pollenkitt, is derived from breakdown materials of an inner layer of the anther. It is added to pollen grains after they are formed and before the anther dehisces. Viscin threads are made up of sporopollenin, the same biopolymer that exine (the outer wall of a pollen grain) is composed of. Viscin threads have points of attachment on an outer layer of the exine called the ektexine. Unlike pollenkitt, viscin threads don’t add new color to pollen grains, nor do they contain scent compounds. Their thickness, length, abundance, and texture are dependent on the species of plant they are found on, much like pollenkitt varies in form and composition depending on species.

pollen strands of tufted evening primrose (Oenothera caespitosa)

Viscin threads evolved independently in three distantly related plant families. These include Onagraceae (the evening primrose family), Ericaceae (the heath family), and a subfamily in the pea family known as Caesalpinioideae (the peacock flower subfamily). Viscin threads are found in many, but not all, of the species in these three families. Some species in other plant families have what appear to be viscin threads but are actually ropy strands of pollenkitt, as they are composed of pollenkitt and not sporopollenin. Because they are made up of the same durable material as exine, viscin threads can be preserved in the fossil record. A paper published in Grana (1996) looked at the morphology of pollen grains with viscin threads from the Tertiary Period and concluded that “this advanced pollination syndrome using viscin threads as a pollen connecting agent” dates back to at least the Eocene and perhaps much earlier.

While pollenkitt’s stickiness adheres pollen grains together, viscin threads are more of a tangling device. Single pollen grains or pollen grain groupings called tetrads become tangled up together and then become entangled with a visiting insect, bird, or bat and carried away to a nearby flower. Disentanglement from the pollinator ideally happens when the threads are brushed against the sticky surface of a stigma. The viscin threads themselves vary by species and family. Micheal Hesse, in a paper published in Grana (1981), describes the threads in Onagraceae as “long, numerous, thin, and sculptured” with “knobs, furrows, etc.,” while those in Ericaceae are thin and smooth and those in Caesalpinioideae are thick and smooth.

smooth azalea, pink form (Rhododendron arborescens)

The length and size of tangled pollen masses also differ by species and can offer clues as to which pollinators visit which flowers. Research published in New Phytologist (2019) looked at the size of pollen thread tangles (PTT) in 13 different species of Rhododendron. They also noted which pollinators visited each species and how often they visited. The researchers found that species presenting pollen in small but abundant PTT were visited by bees, and those with large but few PTT were visited by birds and Lepidoptera (butterflies and moths). Bees also visited the flowers more frequently than birds and Lepidoptera. Bees collect and consume pollen. Between visits to anthers, they spend time grooming themselves, removing pollen clusters from their bodies and packing them into corbiculae (i.e. pollen baskets) for later*. Birds and Lepidoptera don’t groom pollen from their bodies and don’t collect it. In the authors terms, this “suggests pollinator-mediated selection on pollen packaging strategies.” Since flowers pollinated by bees lose much of their pollen in the process, they present it in smaller packages, and since flowers pollinated by birds and Lepidoptera are visited less frequently, their pollen packages are larger.

This is an example of the pollen presentation theory, and is something we will revisit as the Year of Pollination continues.

*This applies specifically to bee species that have corbiculae, and many bee species do not.

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Winter Trees and Shrubs: Sweetgum

Sweetgum is a distinctive tree at any time of year. It stands out among most other deciduous trees with its excurrent growth habit, which gives it a narrowly conical or pyramidal shape. Only in its advanced age does it begin to develop a more rounded and irregular form. Its leaves are star-shaped with either five or seven lobes and span between four and seven inches. Their glossy green color gives way to a wide range of colors in the fall, including yellow, orange, red, and maroon, remaining on the tree for several weeks depending on weather conditions. The fruits are particularly distinct, especially in the winter after the leaves have dropped. Woody balls made up of a series of capsules with pointed beaks hang from long stalks throughout the winter, windborne seeds having been released from small openings in the fall. Without even bothering to look at the twigs, seeing these durable, spiky balls hanging from branches (or feeling them under your feet) is a quick indication that you are looking at a sweetgum.

one of many fall colors found on sweetgum (Liquidambar styraciflua)

Liquidamabar styraciflua (one of the funnest botanical names to say) was previously placed in the family Hamamelidaceae but is now one of the few members of Altingiaceae. Its natural distribution is broad, covering a large portion of the eastern United States and west into Missouri then down into Texas, Mexico, and much of Central America. Outside of its natural range it has been widely planted as an ornamental, and there are several popular sweetgum cultivars currently in cultivation. Both the common and botanical names for this tree refer to the resin found in its bark, which historically has had many uses.

The winter twigs of sweetgum are stout, round, smooth, and yellow-brown to green or olive-green to brown-purple in color. They can also be glossy and feature a few scattered lenticels. Older twigs (or branchlets) are brown at first and then light grey with dark grey lenticels. They are occasionally adorned with corky wings similar to those of bur oak. Because the wings aren’t always present, it can be a fun thing to encounter when you are out looking at twigs.

corky wings on the branchlets of sweetgum

The winter buds of sweetgum twigs are egg-shaped and made up of bud scales with acute tips and ciliate margins. They are green to orange-brown or reddish in color and occasionally sticky. Lateral buds are alternately arranged, are much smaller than terminal buds, and are stalkless and flattened against the twig. They sit above a slightly raised leaf scar that is half-elliptical to triangular in shape and has three distinct vascular bundle traces. The pith of sweetgum twigs is solid, continuous, brownish, and irregularly shaped.

winter twig of sweetgum tree

Sweetgum bark is light to dark grey and is made up of a series of rough, vertically arranged, scaly ridges that become deeply furrowed with age. The mace-like fruits of sweetgum are about one inch wide and, at a glance, are similar in appearance to the seed balls of sycamore trees; however, sycamore seed balls easily break apart when compressed, while the pointed, woody capsules that make up a sweetgum ball are held firmly together and can hold their shape for long periods of time. When these “gumballs” collect on the ground below, they can become a hazard, especially where there is lots of foot traffic. Speaking from experience, they are also obnoxious when operating a mower. This polarizing feature has resulted in bad opinions of the sweetgum tree. Luckily, some people are out there defending it.

sweetgum bark
the persistent fruits of sweetgum

More Winter Trees and Shrubs:

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Getting to Know a Grass – Basic Anatomy and Identification

Have you ever tried to identify a grass? Most of us who like to look at plants and learn their names will probably admit that we often give up on grasses pretty quickly, or just ignore them entirely. They aren’t the easiest plants to identify to species, and there are so many of them. Without close inspection, they can all look pretty similar. Their flowers aren’t particularly showy, and their fruits are fairly forgettable. They are strands or clumps of green that create a backdrop for more intriguing forms of vegetation. Yet, they are among the most ecologically and economically important groups of plants on the planet. And actually, if you can ascend the hurdles that come with getting to know them, they are beautiful organisms and really quite amazing.

Kōura in the Grass

The grass family – Poaceae – consists of nearly 8oo genera and about 12,000 species. Grasses occur in a wide range of habitats across the globe. Wherever you are on land, a grass is likely nearby. Grasses play vital roles in their ecosystems and, from a human perspective, are critical to life as we know it. We grow them for food, use them for building materials and fuel, plant them as ornamentals, and rely on them for erosion control, storm water management, and other ecosystem services. We may not acknowledge their presence most of the time, but we very likely wouldn’t be here without them.

The sheer number of grass species is one thing that makes them so difficult to identify. Key identifying features of grasses and grass-like plants (also known as graminoids) tend to be very small and highly modified compared to similar features on other flowering plants. This requires using a hand lens and learning a whole new vocabulary in order to begin to understand a grass’s anatomy. It’s a time commitment that goes beyond a lot of other basic plant identification, and it’s a learning curve that few dare to follow. However, once you learn the basic features, it becomes clear that grasses are relatively simple organisms, and once you start identifying them, it can actually be an exciting and rewarding experience.

Quackgrass (Elymus repens) and Its Rhizome

Depending on the species, grasses can be annuals – completing their life cycle within a single year – or perennials – coming back year after year for two or more years. Most grasses have a fibrous root system; some are quite shallow and simple while others are extremely deep and extensive. Some species of perennial grasses spread by either rhizomes (underground stems), stolons (horizontal, above ground stems), or both. Some grasses also produce tillers, which are essentially daughter plants that form at the base of the plant. The area where roots, rhizomes, stolons, and tillers meet the shoots and leaves of a grass plant is called the crown. This is an important region of the plant, because it allows for regrowth even after the plant has been browsed by a grazing animal or mown down by a lawn mower.

The stem or shoot of a grass is called a culm. Leaves are formed along the lengths of culms, and culms terminate in inflorescences. Leaves originate at swollen sections of the culm called nodes. They start by wrapping around the culm and forming what is called a leaf sheath. Leaves of grasses are generally long and narrow with parallel venation – a trait typical of monocotyledons. The part of the leaf that extends away from the culm is called the leaf blade or lamina. Leaves are alternatively arranged along the length of the stem and are two-ranked, meaning they form two distinct rows opposite of each other along the stem.

The area where the leaf blade meets the leaf sheath on the culm is called the collar. This collar region is important for identifying grasses. With the help of a hand lens, a closer look reveals the way in which the leaf wraps around the culm (is it open or closed?), whether or not there are hairs present and what they are like, if there are auricles (small flaps of leaf tissue at the top of the collar), and what the ligule is like. The ligule is a thin membrane (sometimes a row of hairs) that forms around the culm where the leaf blade and leaf sheath intersect. The size of the ligule and what its margin is like can be very helpful in identifying grasses.

The last leaf on the culm before the inflorescence is called the flag leaf, and the section of the culm between the flag leaf and the inflorescence is called a peduncle. Like the collar, the flower head of a grass is where you’ll find some of the most important features for identification. Grass flowers are tiny and arranged in small groupings called spikelets. In general, several dozen or hundreds of spikelets make up an inflorescence. They can be non-branching and grouped tightly together at the top of the culm, an inflorescence referred to as a spike, or they can extend from the tip of the culm (or rachis) on small branches called pedicels, an inflorescence referred to as a raceme. They can also be multi-branched, which is the most common form of grass inflorescence and is called a panicle.

Either way, you will want to take an even closer look at the individual spikelets. Two small bracts, called glumes, form the base of the spikelet. Above the glumes are a series of florets, which are enclosed in even smaller bracts – the outer bract being the lemma and the inner bract being the palea. Certain features of the glumes, lemmas, and paleas are specific to a species of grass. This includes the way they are shaped, the presence of hairs, their venation, whether or not awns are present and what the awns are like, etc. If the grass species is cleistogamous – like cheatgrass – and the florets never open, you will not get a look at the grass’s sex parts. However, a close inspection of an open floret is always a delight. A group of stamens protrude from their surrounding bracts bearing pollen, while feathery stigmas reach out to collect the pollen that is carried on the wind. Depending on the species, an individual grass floret can have either only stamens, only pistils (the stigma bearing organs), or both. Fertilized florets form fruits. The fruit of a grass is called a caryopsis (with a few exceptions) and is indistinguishable from the seed. This is because the seed coat is fused to the wall of the ovary, unlike other fruit types in which the two are separate and distinct.

If all this doesn’t make you want to run outside and take a close look at some grasses, I don’t know what will. What grasses can you identify in your part of the world? Let me know in the comment section below or check out the linktree and get in touch by the means that suits you best.

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Randomly Selected Botanical Terms: Glochids

The spines of a cactus are an obvious threat. They are generally sharp, smooth, and stiff; as soon as you are stabbed by one, it is immediately clear that you’ve gotten too close. Sitting at the base of the spines – or in place of spines – on many species of cacti is a less obvious, but significantly more heinous threat. Unless you’re looking closely, this hazard is practically invisible, and the pain and irritation that can come as a result of close contact has the potential to last significantly longer than the sharp poke of a spine. This nefarious plant part is called a glochid, and if you’ve ever made contact with one (or more likely several dozen of them), it’s not something you will soon forget.

Opuntia polyacantha x utahensis

The spine of a cactus is actually a leaf. The area from which a spine emerges from the fleshy, photosynthetic stem of a cactus is called an areole, which is equivalent to a node or bud on a more typical stem or branch from which leaves emerge. In place of typical looking leaves, a cactus produces spines and glochids. Like spines, glochids are also modified leaves, although they appear more like soft, little tufts of hair. However, this unassuming little tuft is not to be trifled with.

Close inspection of a glochid (with the help of a microscope) reveals why you don’t want them anywhere near your skin. While the surface of a cactus spine is often smooth and free of barbs, glochids are covered in backwards-facing barbs. The miniscule size of glochids combined with their pliable nature and retrose barbs, make it easy for them to work their way into your skin and stay there. Unlike spines, glochids easily detach from a cactus stem. Barely brushing up against a glochid-bearing cactus can result in getting stuck with several of them.

Opuntia basilaris var. heilii

Because glochids can be so fine and difficult to see, you may not even be aware they are there. You probably won’t even feel them at first. Removing them is a challenge thanks to their barbs, and since you may not be able to remove them all, the glochids that remain in your skin can continue to cause irritation for days, weeks, or even months after contact. For this reason, cactuses are generally best seen and not touched, or at the very least, handled with extreme care.

Apart from being a good form of defense, the glochids of some cactus species can serve an additional function. Most cactus species occur in arid or semi-arid climates, where access to water can be quite limited. In order to increase their chances of getting the water they need, some desert plants are able to collect water from the air. A few species of cactus do this, and glochids are a critical component in making this happen.

Cylindropuntia whipplei

A study published in the Journal of King Saud University – Science (2020) examined the dew harvesting ability of Opuntia stricta, commonly known as erect prickly pear. As described above, the spines of O. stricta are smooth, while the glochids are covered in retrose barbs. Both structures are waterproof due to hardened cell walls and cuticles. However, due in part to the conical shapes of both the glochids and their barbs, water droplets from the air are able to collect on the tips of the glochids. From there, the researchers observed the droplets in their travel towards the base of the glochids. As they moved downward, small droplets combined to form larger droplets.

At the base of the glochids are a series of trichomes, which are small hair-like outgrowths of the epidermis. The trichomes do not repel water, but rather are able to absorb the droplets as they reach the base of the glochids. For a plant species that receives very little water from the soil, being able to harvest dew from the air is critical for its survival, and this is thanks in part to those otherwise obnoxious glochids.

See Also: Prickles

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Randomly Selected Botanical Terms: Prickles

Let’s start by getting something out of the way: roses have prickles, not thorns. However, just like peanuts aren’t actually nuts and tomatoes are actually fruits, our colloquial terms for things don’t always match up with botanical terminology. This doesn’t mean that we should be pedants about things and go spoiling a friendly dinner party with our “well, actually…” corrections. If you hear someone saying (or singing) something about every rose having its thorn, it’s okay to just let it go.

So why don’t roses have thorns? And what even is a prickle anyway?

Plants have a way of modifying various body parts to form a variety of features that look like something totally new and different. When the development of these features are observed at a cellular level, we find that what once may have grown into something familiar, like a stem, is now something less familiar, like a thorn. A thorn, then, is a modified stem. Stem tissue was used by the plant to form a hardened spike. Thorns help protect a plant from being eaten, so going through the trouble of producing this feature is a benefit to the plant.

thorns of hawthorn (Crataegus sp.)

Spines and prickles are similar features to thorns and serve a similar purpose, but they have different origins. Spines are modified leaf or stipule tissue (the spines on a cactus are actually modified leaves). Prickles are outgrowths of the epidermis or bark. In plants, epidermis is a single, outer layer of cells that covers all of the organs (i.e. leaves, roots, flowers, stems). Outgrowths on this layer are common and often appear as little hairs. The technical term for these hairs or hair-like structures is trichomes.

the stems of staghorn sumac (Rhus typhina) are covered in dense trichomes

Prickles are much like trichomes, but there are usually less of them and they are hardened and pointy. They can be sharp like a thorn or spine and so are often confused for them. (Spines are also confused for thorns, as is the case with Euphorbia milii, whose common name is crown of thorns but whose “thorns” are actually spines.) As stated above, their cellular origin is different, and unlike thorns and spines, prickles don’t have vascular tissue, which is the internal tissue that transports water and nutrients throughout all parts of the plant. In general, prickles can be easily broken off, as they are often weakly attached to the epidermis.

Prickles are most commonly observed on roses and come in a variety of shapes, sizes, and colors.

Prickles on roses are commonly called thorns, and that’s okay. Thorn is perhaps a more poetic word and easier to relate to. But really, I’m torn and forlorn that they aren’t thorns. It puts me in a pickle trying to rhyme words with prickle.

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Winter Trees and Shrubs: Tulip Tree

At first glance, a tulip and a tulip tree couldn’t be more different. One is a bulb that puts out fleshy, green leaves in the spring, topped with colorful, cup-shaped flowers, barely reaching a foot or so tall. The other is a massive, deciduous tree with a broad, straight trunk that can grow to nearly 200 feet tall. But if you can get a look at the flowers, seed heads, and even the leaves of this enormous tree, you might see a resemblance – at least in the shape of these features – to one of our most popular spring flowering geophytes.

Tulip tree (Liriodendron tulipifera) is distributed across the eastern United States and has been planted widely outside of its native range. Also commonly known as tulip poplar, yellow poplar, and whitewood, it is a member of the magnolia family and is one of two species in its genus (the other being Liriodendron chinense – a tree found mainly in China). Many (if not most) deciduous trees of North America have small, inconspicuous flowers, but tulip trees – like its close relatives, the magnolias – have relatively large, showy flowers. The trouble is actually getting to see them since, at least on mature trees, they are borne in a canopy that is considerably taller than the average human.

Tulip tree flowers are cup-shaped, yellow-green and orange, with a series of prominent stamens surrounding the carpels which are attached to a long, slender receptacle giving it a cone-shaped appearance. As the flower matures into fruits, the tulip shape of the inflorescence is maintained as the seeds with their wing-like appendages form a tight, cone-like cluster that opens as the seeds reach maturity. The wings aid in dispersal as the seeds fall from the “cone” throughout the winter.

seed head of tulip tree (Liriodendron tulipifera)

The four-lobed leaves of tulip trees also form a vague tulip shape. They are alternately arranged, bright green, and up to five or six inches long and wide, turning yellow in the fall. Two prominent, oval-shaped stipules surround the stem at the base of the petiole of each leaf. These stipules come into play when identifying the leafless twigs of tulip trees during the winter months.

leaf of tulip tree (Liriodendron tulipifera) in late summer

The winter twigs of tulip trees are easily recognizable thanks to their duck bill shaped buds which are made up of two wine-red, violet, or greenish bud scales. The terminal buds are considerably larger and longer than the lateral buds, some of which are on little stalks. The twigs are smooth, olive-brown or red-brown, with just a few, scattered, white lenticels. Leaf scars are rounded with a dozen or so bundle scars that are either scattered or form an irregular ellipse. Pronounced stipule scars encircle the twig at the location of each leaf scar. Twigs can be cut lengthwise to reveal pale white pith that is separated by a series of diaphragms.

winter twig of tulip tree (Liriodendron tulipifera)
top right: the chambered pith of black walnut (Juglans nigra); bottom left: diaphragmed pith of tulip tree (Liriodendron tulipifera)

The bark of tulip trees can be easily confused with that of ash trees. Young bark is smooth and ash-gray to grayish green with pale, vertical cracks. As the tree matures, the cracks develop into furrows with flat-topped ridges. The ridges grow taller and more peaked, and the furrows grow deeper as the tree reaches maturity. In the book Winter Botany, William Trelease compares the mature bark of tulip trees to a series of parallel mountain ranges with deep gullies on either side.

maturing bark of tulip tree (Liriodendron tulipifera)

Perhaps even as tulips are blooming, the buds of tulip trees break to reveal their tulip-shaped, stipule bearing leaves. This makes for an interesting show. In The Book of Forest and Thicket, John Eastman describes it this way: “from terminal buds shaped like duck bills, successions of bills within bills uncurl and unfold, revealing a marvel of leaf packaging.”

More Winter Trees and Shrubs:

The photos of tulip tree were taken at Idaho Botanical Garden in Boise, Idaho.

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Drought Tolerant Plants: Blue Flax

“Lewis’s prairie flax is a pretty garden ornamental suited to hot, dry sites. Each morning delicate sky blue flowers open on slender arching stems, only to fall off in the afternoon and be replaced by others the next morning. In spite of its fragile appearance, it is quite sturdy and may put out a second flush of blossoms on new growth in late summer.” — Common to the This Country: Botanical Discoveries of Lewis and Clark by Susan H. Munger

When selecting plants for a waterwise garden, it is imperative that at least a portion of the plants are easy to grow and maintain and are adapted to a wide variety of conditions. This will ensure a more successful garden, both functionally and aesthetically. Luckily, there are a number of drought-tolerant plants that pretty much anyone can grow without too much trouble. Blue flax, in my opinion, is one such plant.

You may be familiar with flax as a culinary plant, known for its edible seeds which are used to make flour (i.e. meal) and oil. Or perhaps you’ve used linseed oil, a product of flax seeds, to protect wooden, outdoor furniture or in other wood finishing projects. You may also think of linen when you think of flax; and you should, because linen is a textile made from the fibrous stems of the flax plant. All of these products generally come from a domesticated, annual flax known as Linum usitatissimum – a species that has been of benefit to humans for millenia. Various species of flax have also been planted for erosion control, fire breaks, forage for livestock, and in pollinator-friendly gardens. Flax seeds, a common ingredient in bird seed mixes, provide food for birds and other small animals. All this to say, humans and flax share a long history together, and it deserves a place in your garden.

The flax species profiled here is actually two species: Linum lewisii and Linum perenne. That’s because these two species look nearly identical and are both used as garden ornamentals and in wildflower seed mixes. They are also both known as blue flax, among myriad other common names. Due to their similiarity, L. lewisii is considered by some to be a subspecies of L. perenne.

Linum lewisii is found across western North America and received its name after being collected by a member of the Lewis and Clark Expedition. The plant collection was brought back from the expedition and determined to be new to western science. It was described and named by Frederick Pursh. Linum perenne is a European species which was introduced to North America as an ornamental and has since become widely naturalized. In 1980, a naturalized selection of L. perenne was released for use in restoration plantings under the cultivar name ‘Appar’ with the understanding that it was L. lewisii. A genetic study later revealed that the cultivar was instead L. perenne. The study also provided evidence that “North American Lewis flax and European perennial blue flax are reproductively isolated,” suggesting that they are indeed two separate species.

Despite being separate species, telling them apart can be a challenge. Blue flax plants grow from a taproot and woody base and are multistemmed, reaching two to three feet tall. The stems are thin yet stringy, wiry, and not easily torn, which helps explain why flax is such a good plant for making textiles. Short, slender leaves are alternately arranged along the length of the stems, while flower buds form at the ends of stems in loose clusters. Flowers bloom early in the day and are spent by the afternoon. They are 5-petaled, saucer-shaped, and a shade of blue – from whitish blue to deep blue – depending on the plant. Small, round, 10-chambered seed capsules form in the place of flowers, each chamber housing one or two flat, shiny, dark brown seeds. Flowers bloom daily in succession up towards the ends of stems even as the fruits of spent flowers lower on the stalk mature.

seed capsules of blue flax

A close look at their flower parts is really the only way you might be able to tell these two species apart. Blue flax flowers have five stamens topped with white anthers and five styles topped with little, yellow stigmas. The flowers of L. lewisii are homostlyous, which means their styles are all the same length and are generally taller than or about the same height as the stamens. The flowers of L. perenne are heterostylous, which means their flowers can either have styles that are much longer than their stamens or stamens that are much longer than their styles. Each plant in a population of L. perenne has either all long-styled flowers or all short-styled flowers. In a mixed population of L. perenne and L. lewisii, separating the long-styled L. perenne plants from the L. lewisii plants presents a challenge (at least for me).

long-styled blue flax flower
short-styled blue flax flower

Due to the similarity of these two species, it’s easy to see how the plants or seeds of blue flax could easily be mislabeled and sold as one species even though they are the other species. This could be a problem in a restoration planting where seed source and identity is critical, but in your garden, it’s really no big deal. Both species are great for waterwise and pollinator gardens. They are equally beautiful and easy to grow and care for. If nothing else, perhaps the challenge in identifying them will encourage you to take a closer look at your flowers and familiarize yourself with their tinier parts – an act all of us amateur botanists could stand to do more often.

The photos in this post were taken at Idaho Botanical Garden in Boise, Idaho.

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