Native Plants, Habitat Restoration, and Other Science Snippets from Athens, Georgia

Saturday: 9 June 2012

Watching for the Beggar-lice  -  @ 06:59:59
Let's say you wanted to learn a little plant taxonomy method and madness. If you were in the Eastern US, east of the Rockies, that is, you could then do worse than to pick the genus Desmodium, or beggar-lice, or beggar-ticks, or ticktrefoil, or stick-tights. There are probably as many variations on the name as soda, or pop, or co-cola, as older languishing southerners might say. Everyone knows what you're talking about though - it's the plants that make those flat hairy seeds that stick to your socks.

(You could do this anywhere, and with any group of plants, but my choice of Desmodium is made on the basis of its homely characters and diversely (but not ridiculously) challenging speciation. Doubtless there are western analogs to this group of leguminous plants.)

For Desmodium, that's one of the first things you'd learn - the fruit is called a loment, which is really just an indehiscent segmented legume. How deep the segmentations, how hairy, and so forth, are a portion of the keys that allow you to enter the world of the 76 nearctic species of Desmodium that are listed in USDA Plants.

Why else Desmodium? Well, it turns out to be a fairly important wild animal food, probably both for browsing (large mammals) and seeds (quail and other birds, small mammals). It's a legume, so it nitrifies the soil. It has pretty flowers! Some species are a pretty ground cover. And it's something everyone who goes outside knows about, even though they actually know nothing about it, and you can help them out!

And at least from USDA Plants, the genus contains no noxious species in the US, something that might seem remarkable from the point of view of anyone who gets a zillion seeds on their socks. But remember that it's not always all about *you*, and the word "noxious" certainly doesn't apply to a plant genus so useful in other respects.

Georgia is specifically listed by USDA Plants as having 23 species. I figure at least ten, and possibly as many as eighteen, might be found on our property. None, for us, should be non-native (there is only one non-native Desmodium species in Georgia, and only six overall). So I'm sort of casually setting about to learn them. Long ago we identified the shrubbier Desmodium paniculatum, panicled leaf ticktrefoil.

Here's a new one that didn't really need the key. It's our earliest flowerer, Desmodium rotundifolium, and from the name you can tell it must have round leaves (or leaflets), and so it does! Much more so than most Desmodium species, and that's what caught my attention. The stems trail along the ground, vinelike, and that's also different from most beggar-lice. It is how it gets its common name - prostrate ticktrefoil.

I've only found this in one place here, a few feet up the bank on Upper SBS Creek - just a patch of plants covering the ground.

There are many Desmodium species with much more localized ranges. D. rotundifolium is found over at least a third of the US and Canada. (From the Desmodium USDA Plants page.)

See the nice pink pea-like flowers! There are surely some differences to be found among the Desmodium species. Most of the business part of the flower is in the keel, the lower set of petals under the banner (the upper two fused petals). If I didn't already know this was D. rotundifolium, I'd need to look at the stamens. They might be monadelphous or diadelphous (stamens fused into one or two structures, at the filament), and that would be an early key character.

This was just a fortuitous flower and fruit shot, with one flower head on, and the other showing its better side. There's also a developing fruit - the loment, with a seed developing in each segment. There is no stipe, that is, a lengthy stem that connects the loment to the calyx, and that's another key character.

These plants used to be in the genus Meiobomia. That apparently violated some dusty rule, and Desmodium was chosen to replace it. But it turns out that the species in the southeast US (at least) cluster into five non taxonomic groups, and one of these groups is very distinctively different from the other four. If it should be determined that those differences are sufficient, then the first, smaller group would continue to be Desmodium, but the other four groups would again be given the old Meiobomia genus name.

In our case, we have species represented in all five taxonomic groups. Other than D. rotundifolium, no other is flowering yet, but there are a large number of populations of unidentified species I'm watching out for.

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