Mystery Plant! #780

John Nelson

Posted 6/19/24

By John Nelson

An early-morning walk is a blessing for the whole day.
–Henry David Thoreau
(Photo by John Nelson.)

I agree! And now that it’s summer, it warms up really fast around here where I live, so a morning walk is indeed the best time for me. My neighborhood is called “University Hill”, and it is indeed a hill, with plenty of places to stroll: always something new to see, whatever the season. And being a botanist, I don’t have to go very far to see interesting things. Like the front yard of one of my neighbors.

She lives in an old house (with a historic marker) about 3 blocks away. Her front yard has been turned into a botanical garden, a garden that seems to have few rules about how it is put together. She has tomatoes and hot peppers growing in various containers, along with just about any herb you can think of. Toward the sidewalk is a grove of blackberries, now ripening. Near the front door she has some tall cut-leaf rudbeckias; I’ve never seen these growing in a garden before. But the best part, as you might expect, is what we have as this week’s Mystery Plant.

(Photo by John Nelson.)

Maybe she started it from seed several years ago, I have no idea. Now the plants are taller than I am, and quite impressive, in a bright golden, summery way. It’s a perennial species which forms rhizomes. The stems tend to be square in cross-section, with rather sharp angles. (I know what some of you are thinking: but no, not everything with square stems is in the mint family.) These stems tend to be a bit scratchy and hairy from the bottom to the top, and the leaves are opposite (two at a time on the stem). The blades get to be nearly a foot long, generally with coarse teeth, and with a rather sandpapery feel. About midway up the stem, each pair of these opposite leaves will be totally fused to each other at their bases: what an odd way for plants to do it! We say that the leaves are “perfoliate”, which is just fancy talk for a stem appearing to grow through the leaves. (You may know of some Eupatorium species that do this, too.) The depression thus formed between a pair of leaves is deep enough to hold a bit of rain water, as it turns out, but we don’t know if this curious arrangement provides any real advantage to the plant.

And then the upper branches produce magnificent blooms. One look at these heads of flowers and you’ll know instantly that yes, this is yet another member of the sunflower family. Each head is bounded by a series of bracts at the base. Ray flowers, about 20, ring each head. These flowers are fertile, and produce fruits. Each fruit resembles a flattened sunflower seed, with a narrow wing on each side. The disk flowers in the middle of the head, in this case, produce pollen, but no ovules, and hence, no fruits.

I can’t promise that you’ll see this plant on your next morning walk, but I’m sure you’ll see something worthwhile. Just watch out for the fire-ants.

[Answer:  “Cup plant,” Silphium perfoliatum]

John Nelson is the retired curator of the Herbarium at the University of South Carolina, in the Department of Biological Sciences. As a public service, the Herbarium offers free plant identifications. For more information, visit or email

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