Weekly Weed, July 29: Carolina horsenettle

Alas, with this weed, I will be taking a hiatus from the weekly weed post for a time. Still be on the lookout for new nature-related posts, as I’ll continue to post photos of my botanizing adventures!

I haven’t seen this next weed very frequently, but since it is a widespread and fairly easy-to-recognize species, I decided to write about it. Carolina horsenettle (Solanum carolinense), like tomatoes and peppers, is a member of the nightshade family, Solanaceae. Indeed, the flowers of this plant are very similar to those of tomatoes and peppers with five (sometimes six) papery white petals that are united into a tube for about half of their length, but then spread out into a flat, starry shape. Five thick, bright yellow anthers (male, pollen-producing parts) protrude from the center of the star, as well as the less conspicuous style and stigma (female, pollen-accepting parts). These yellow-on-white flowers are a dead giveaway that this plant is in the genus Solanum.

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Carolina horsenettle – Solanum carolinense

Even the non-reproductive parts of this plant are easy to distinguish. The whole plant is armed with spines, from the thickest stalks to the rachises (central veins) of the leaves. The leaves are roughly the shape of an extended triangle or fat, pointy feather, though they are most easily recognized by their wavy lobes. They are also strongly veined and, as I mentioned before, super spiny!

The fruits of this plant also look like tiny, albeit yellow, tomatoes…but don’t chow down on them! These plants contain high levels of toxic solanine, like modern-day tomatoes once did before we domesticated them. Maybe in a couple hundred years we can selectively breed the poison out of them, but until now, leave them for the birds and the rodents.

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Carolina horsenettle – Solanum carolinense
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Weekly Weed, July 22: Tropical bushmint

The weeds just keep coming through the summer, and I suppose I’ll just keep writing about them! This week I thought I’d describe a conspicuous weed I observed flowering on a foraging walk with friends here in the Florida panhandle: tropical bushmint. Its Latin name was recently changed to Cantinoa mutabilis from Hyptis mutabilis to more accurately describe evolutionary relationships between species in the genus Hyptis. Maybe the taxonomists will lump it back into Hyptis at some point, but for now, it might be best to know both names.

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Tropical bushmint – Cantinoa mutabilis

True to its name, Cantinoa mutabilis is in the mint family (Lamiaceae), easily discerned from its opposite leaves, square stems, and the flowers borne in the leaf axils (where the leaf meets the stem). These flowers are small, but numerous, usually bluish to whitish-purple with the typical bilaterally symmetric flowers of a mint (a fat bottom lip, a curled top lip, and two stubby wings, in this case). While the flowers may not be impressive, the stature of the plant is certainly striking, growing easily 4-5 feet (~1.5 meters) tall or taller. It has tough, lignous stems with many (opposite) branches and deltoid leaves, and the entire plant is covered with tiny, prickly hairs.

While it doesn’t seem to be a huge nuisance yet, this introduced species does have all the makings of an invasive: prolific reproduction, hardiness, and opportunism. I have found it in a completely exposed powerline corridor and in sunny margins of damp woods, and it certainly does not seem to have trouble getting around. Its seeds are smaller than poppyseeds and hundreds, if not thousands, are produced per healthy plant. So far Cantinoa mutabilis has only shown up in warm climates in the Southeastern states, but it might behoove us to watch its spread closely.

Weekly Weed, July 11: Muscadine

Muscadine (Vitis rotundifolia) is like that weird cousin who always seems to be around, just gets in the way, and doesn’t do anything with his life, yet you have to tolerate him because he’s part of the family. This hardy vine is everywhere in the Southeast: scrambling through dry shrubbery, climbing through moist forests, you name it. Sometimes it takes the form of a delicate vine in the bushes, sometimes it forms pendulous, Tarzan-worthy vines as thick as your wrist. It takes advantage of disturbed areas such as beside interstates and completely covers the trees growing there. Supposedly, this plant produces dark, grape-like berries that can be eaten (if you get past the tough skin) or made into wine or juice; however, I’ve never seen a muscadine with anything more than a handful of sad, pea-sized fruits hanging on it.

(for the record, I don’t have any cousins like that, but it’s something I can easily imagine)

Maybe muscadine and I just got off on the wrong foot. I had just moved from Portland, Oregon, where English ivy is the local (weed) supervillain, and the growth habit of muscadine (a liana, or woody vine) seemed eerily similar. Flashes of previous hours spent pulling that onerous ivy (and pulling muscles doing so) raced through my mind.

In reality, muscadine can be a pleasant sight, especially its new growth in the spring. The leaves are a lovely heart-shape with large, confident teeth along the margins. Its hard to mistake the distinct leaf shape and viny growth for many other species in the region, although there are many vine species in Florida.

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Muscadine – Vitis rotundifolia

Most often you’ll find muscadine when it has already grown green and robust. It hangs on trees, fences, shrubs, old houses, old cars…you name it. It’s another case of an opportunistic native. While other natives can’t stand the throes of habitat loss due to human activity, muscadine thrives.

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Muscadein vine – Vitis rotundifolia. The large, oval leaves in the background are not part of the Vitis, but belong to another weed genus, Elephantopus.

Weekly Weed, July 4: Virginia Pepperweed

In honor of Independence Day (in the U.S.), I’ve chosen a native weed with an entrepreneurial spirit comparable to the American Way. Its influence has spread from the U.S. mainland and is now introduced in all continents except Antarctica (for better or for worse). In my experience, this plant is opportunistic and tenacious, growing in many odd, disturbed areas and sometimes forming short, dense clusters that grow and regrow even after mowing. The whole plant varies in size, ranging from very short (when mowed) to very tall (up to 70 cm!), and it usually sends multiple reproductive stalks up from its robust base.

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Virginia pepperweed – Lepidium virginicum

One generally recognizes this plant by its fruits rather than its flowers. Like many members of the mustard family (Brassicaceae), its flowers are minuscule, four-petaled white flowers with long pedicels popping off of a central stalk. The fruits, however, are strikingly flat discs borne also on those long pedicels but now perpendicular to the main stalk, forming a thin, overall cylindrical shape. The inflorescence just keeps growing and growing; as the flowers on the bottom mature into fruits, new flowers form at the top of the cluster and wait patiently to be pollinated by some little gnat or fly.

Pepperweed gets its name from the flavor of its young fruits which, predictably, taste like pepper! The plant itself is edible as a potherb (i.e., green thing you throw in soup) and, although I haven’t tried it (yet!), I’m sure including the fruits would spice up any dish nicely.

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Virginia pepperweed – Lepidium virginicum

Weekly Weed, June 24: Bahiagrass

My posts over the past few months might lead you to believe that I have a personal bias toward dicots, but that’s not true! Grasses are actually one of my favorite things…they’re just a lot harder for the casual observer to identify and thus more difficult for me to describe. This week’s weed, however, isn’t too hard to recognize: introducing the beautiful and prolific Bahiagrass, Paspalum notatum.

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Bahiagrass spikes – Paspalum notatum

Bahiagrass is the most optimistic grass you will ever see. To me, it looks like it has two happy arms thrown up in the air and is shouting “yay!” It’s also optimistic about where it can grow: everywhere! This species thrives wherever there is space and plenty of sun, especially disturbed areas like roadsides, road medians, and lawns. It grows tall and strong, the paired spikes of spikelets (yes, those are the technical terms) rising up in a purplish “V” waving up to a meter off the ground. The purple color of the spikes is due to the plant’s feathery stigmas (female parts) and violet anthers (male parts) emerging from the hard, green, leaf-shaped spikelets. Grasses are almost exclusively wind-pollinated, and the fuzzy texture of the stigmas maximize their surface area, increasing the chance of catching passing pollen. Accordingly, the anthers born on long filaments that dangle in the wind help the plant spread its pollen.

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Bahiagrass – Paspalum notatum

Bahiagrass is not native to the U.S., although it seems perfectly content to call most of the U.S. Southeast home. It originally comes from South America and was introduced in the early 1900s as a pasture grass because of its lush leaves and tolerance to heat. I have few qualms with this species’ new residence, but maybe that’s just because it looks so happy.

Weekly Weed, June 18: Ticktrefoil

As recommended by a friend, this week’s focus is a diverse, widespread genus in the pea family (Fabaceae): Desmodium. (If it seems like Fabaceae has received a lot of attention in this weekly weed blog, that’s correct! The pea family contains many a hardy weed.) The common name of most plants in the genus Desmodium is “ticktrefoil,” though there is one exotic species (to the U.S.) with the colorful common name “zarzabacoa comun.” (I don’t know about you, but to me that sounds like the name of the next Kentucky Derby winner.)

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Zarzabacoa comun – Desmodium incanum

From my understanding of these plants, I believe “ticktrefoil” is a combination of “tick-“, because the seeds cling to your pants like certain onerous, blood-sucking pests, and “trefoil,” which pertains to a three-parted structure. In the case of Desmodium, this three-parted structure is the leaves.

Desmodium is a fun example of how a certain “body plan” can take different forms, yet retain the essential elements of the genus. The leaves are all trifoliolate (three-parted) and have smooth margins (leaf edges), but they can be long and thin, round, or ovate (oval-shaped). Often, the leaves are whitish around the internal veins and may appear minutely soft or fuzzy.

The flowers are adorable: pink or purple with a showy, flattish banner raised above wings and keel folded together.

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Desmodium spp. – Ticktrefoil

The fruits of Desmodium are quite interesting. Like a pea pod, they grow together in a long line of seeds surrounded by minutely prickly carpel walls. Unlike a pea pod, the carpel walls are constricted between each seed, forming a chain of round or diamond-shaped individual pouches. When mature, the pouches easily split from one another, carried here and there by passing animals, wind, or hikers’ pants. This type of fruit, which is dry and consists of many small “mericarps” is called a “schizocarp” (schizo– is Greek for “split” or “cleft”). Desmodium fruits in particular are called “loments” because they break from one another between segments on a long line of fruits, but botanists are notorious for inventing really specific words for really specific plant characteristics, so I’m sure calling them “schizocarps” will impress your non-botanists friends just as much as the more specific term “loments.”

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Desmodium fruits (loments)

Keep your eye out for these subtly showy weeds with three leaflets, small pink pea flowers, and segmented pea-pod-like fruits. Or, at least, pay attention to the annoying little seeds that get stuck to your legs when you walk through the weeds. Some of them might be pieces of Desmodium loments!

Weekly Weed, June 15: White sweetclover

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White sweetclover – Melilotus albus

Today we turn to one of my old favorites, Melilotus albus. I’m not sure exactly why I like this plant…perhaps its the poetic name, the cheerfulness of its white flowers, or the robustness of its growth despite growing in the harshest of environments.

White sweetclover is a tall, somewhat lanky member of the pea family (Fabaceae) with stereotypical trifoliolate (three-leaflet) leaves and non-stereotypical spikes of tiny papilionaceous flowers (like those described in one of my earlier posts). Each flower has a banner, wings, and a keel. Also like other legumes, the fruit of this species is a pod; however, these pods are short and squat: not much bigger than the flower itself. Like the flowers, obviously these too are borne on the long straight spikes at the ends of the plant’s spindly branches.

I first encountered white sweetclover in Oregon when I was coordinating an ecological monitoring project on a sketchy abandoned riverfront we called River Campus. River Campus had once been the site of lumber manufacture, concrete batching, soap manufacture, hazardous waste storage, and sandblasting operations, to name a few. The place was bare and potentially toxic in places, dry from unfiltered rays of the sun and riverfront wind…but the sweetclover didn’t care! It popped up all over, forming jungles in excess of 6 feet high in moister places, which was remarkable for the barrenness of this landscape.

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White sweetclover – Melilotus albus

Similarly, in Florida, I’ve found sweetclover springing to life in dusty abandoned lots and along the side of exposed trails. Dry seems to be its forte; its thick, ligneous stems prevent wilting, and its small leaves prevent losing excess water from the leaves. As you can see, it also reproduces prolifically, producing thousands of fruits per plant, which explains why one can find it across the entire United States!

P1230863Melilotus albus

There is also a yellow version of this plant, Melilotus officinalis, although I personally found the white species to be more common.

Weekly Weed, June 11: American beautyberry

If you live in the Southeastern U.S. and wander out into a city park or other semi-disturbed area, there’s a good chance you’ll find this weedy, native shrub amongst the invasives. When flowering, this plant is somewhat inconspicuous in the spring if you’re not looking for it: it has clusters small, pale pink flowers growing the leaf axils (where the leaves meet the stem). Come fall, however, you’ll be struck by its appearance. Where those tiny, unassuming flowers once sat, now tight bunches of uncanny magenta berries huddle together, like purple caviar cemented to the green stems. Unlike caviar, these berries taste like sawdust. Although they are technically edible, I would not recommend them.

A couple things about this plant are worth remarking upon. First, it is actually quite easy to identify in the field, even when it isn’t sporting feathery flower clusters or globs of purple berries. It has simple leaves (i.e. not broken up into leaflets) with toothed margins (edges) and long petioles (leaf stems). The leaves grow opposite to one another along each stem, and the pairs are widely spaced to make room for the broad leaves. If you look up close, e.g., using a hand lens or magnifying glass, you’ll find that the whole plant is covered with stellate (star-like) or dendritic (tree-like) trichomes (hairs), giving the leaves and stems a minutely fuzzy appearance. Trichomes are ubiquitous throughout the plant kingdom and are generally thought to protect plants from threats such as herbivory and dehydration. They come in many shapes and sizes, but in American beautyberry, they results in a distinct leaf texture that can be used to identify the foliage.

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Microscope view of leaf trichomes. These are much smaller than American beautyberry trichomes and are the “glandular” type rather than “stellate” or “dendritic” (PC: Louisa Howard via Wikimedia)

Second, because I can’t help mentioning something about the taxonomy of the plants I study: the same features I described above also indicate that this species is a member of the mint family, Lamiaceae…or is it? The genus has historically been placed in the Verbenaceae (the verbena family, which does share many characteristics with mints), until molecular phylogenetic work indicated that it was distinct from the latter.

And third, if you’re anything like me and have already received your fair share of bug bites this summer, good news! American beautyberry contains several mosquito-repelling compounds, including one patented by the USDA, callicarpenal. I’m definitely going to try rubbing some leaves on my clothes next time I’m out in the forest!

Weekly Weed, June 2: Fleabane

While I generally like to present individual species with these posts, there are just certain genera that almost can’t be identified in the field. (Or rather, anyone casually reading a nature blog probably isn’t interested in toting dead plants into a lab and ID’ing them under a dissecting microscope). Thus, this week I’m introducing the genus Erigeron, commonly called “fleabane.” Species of the genus Erigeron can be readily distinguished from other daisy-like flowers by the shape and number of their petals. While the common English daisy (Bellis perennis), widespread in lawns throughout the northern U.S., also has bright yellow disc flowers (the center of the “flower”) and numerous white petals, Erigeron‘s petals are thinner, less bowed, and pointier at the ends, often looking more like thick hairs than flower petals. The photo on the left, below, is a daisy, while the photo on the right is fleabane.

Fleabanes are generally a lot taller than daisies, as well…I’ve seen them close to a meter high! Oxeye daisies also get this tall, but they have much broader petals, like so:

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Leucanthemum vulgare – Oxeye daisy (aka NOT a fleabane!)

Admittedly, distinguishing fleabanes from other white/purple-petaled Asteraceae can be a headache–not to mention distinguishing fleabane species from one another–but if you find a tall, thin plant with tons of skinny, whitish petals, there’s a pretty good chance that it’s Erigeron, especially since there are over 520 species in the genus!

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Another fleabane (Erigeron)

Short post this week, but I hope you enjoy the photos!