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Can you identify this week's mystery plant?

MysteryPlant621

Can you identify this week’s mystery plant?

Photo by Linda Lee

[Answer: “Swamp milkweed," Asclepias perennis]

Yesterday! An early summer field trip, deep into a swamp in Allendale County, South Carolina, not too far from the Savannah River.

It was almost noon, and the mixed clouds made it quite pleasant, not hot at all. Up on the high ground, it was open and bright, but scrambling down the bluff onto the bottomland, the swamp was still dark, with a dense canopy overhead. Here and there, slanting sunbeams cut through the gloom and the golden spider webs, and occasional ghostly clouds of mist floated over the damp ground. It was easy walking around, due to low water, and we were far enough from any guts (or “sluices” as my hiking buddy likes to say) that there was no need to be wading. Rather, plenty of downed logs, some quite rotten, offered obstacles, along with thousands of bizarre, tortuous knees of the cypress and tupelos. One would think it would be a perfect day for snakes, but we didn’t see a single one. (On the other hand, it was a pretty good day for the deer flies, which were starting to get happy.) The swamp was quiet, too…except for the occasional scolding from a wren, and of course, the sweetly monotonous buzz of a cicada, philosophizing somewhere on a branch. There was a brilliant yellow swamp canary that flew up to inspect me, and then nervously vanished into the foliage. Occasional damsel flies danced through the sunbeams. A crawling millipede, a pale orange mushroom. A chewed-up crawfish. For all the life present in this setting, and for being surrounded by plants, there weren't many flowers to see. Except for this one.

This is a native species of southern bottomland forests, and it’s one of the showiest wildflowers a swamp can offer. It’s an herb from thick, knotty roots, growing on open mucky ground. It can obviously tolerate considerable shade, as well as waterlogged soils. The leaves are narrow and smooth, and opposite (that is, two at a time) up and down the stem. When the stems are broken, thin, milky fluid oozes from the wounds. The flowers are quite elegant and star-like, held in a dense cluster with all the flower's stalks essentially arising from a single point. (We call such a cluster an "umbel.") Usually one or two clusters are present, sometimes three or more. Interestingly, only a few flowers per plant --frequently only one-- will achieve successful pollination and ultimate fruit production. The fruit itself is a pod (actually called a "follicle"), slender and smooth, pointed at both ends, and hanging. This pod will eventually split open along one seam, releasing dark, slightly elliptical seeds. Our Mystery Plant has plenty of easily recognized and well-known relatives, which also have milky fluid, and flowers in umbels, but whose seeds are equipped with a delicate wispy parachute of long, silky hairs. It’s a bit odd within its group of relatives, in lacking this parachute. You can find our shady swamp-lover along the Atlantic coastal plain from South Carolina to northern Florida, and west to the Mississippi River, as far north as southern Indiana. ©JohnNelson2021

John Nelson is the curator of the A. C. Moore Herbarium at the University of South Carolina, in the Department of Biological Sciences, Columbia SC 29208.

As a public service, the Herbarium offers free plant identifications. For more information, visit www.herbarium.org or call (803) 777-8196, or email nelson@sc.edu.

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