Sedges have edges
Rushes are round
I’ve heard this expression for years, but never gave it a lot of thought. Suddenly I found myself trying to use it for plant identification. I found one complete version here
“Sedges have edges, rushes are round, grasses are hollow right up from the ground.”
and a few other variations elsewhere, with all the variations in the grass description. The reason for remembering this poem is this little plant.
After all, grasses and sedges are a significant part of a savanna (see quote in right-hand column), and it’s about time I started identifying a few of them. I thought this one would be easy because of its white top. I also thought, at first, it was a grass. Then I felt it. It has a solid, round stem. So I thought it was a rush. But I was wrong on both counts.
After a few random searches on the web, and without trying to be systematic about identifying the plant, I put it on the back burner and stopped thinking about it except to smile whenever I saw it. Then, by accident, I stumbled across this site, which gave me a scientific names not only for this plant but also for an intriguing cultivated plant in our area, known locally as the “resurrection plant.” But that’s for another time.
So it turns out that this plant is a sedge with a round stem, the White-topped Sedge, Rhynchospora colorata.
We’ll get back to the “edges” bit later, but for now I need to educate myself about sedges.
The White-topped Sedge is within the Cyperaceae Family
Sedges belong to the large (4,000 species, 70 genera), widely distributed family Cyperaceae (wikipedia). The water chestnut (Eleocharis dulcis) is a sedge. Ancient Egyptians made their writing material from the papyrus sedge (Cyperus papyrus). As wikipedia continues to list “well-known” sedges, it mentions today’s plant, the White Star Sedge [another common name for White-topped Sedge] (Rhynchospora colorata). Well-known, perhaps, but not known to me until the accidental web find. It is, however, distributed beyond the tropics, being found in Tennessee (including the Oak Ridge Reservation area), Texas, and Florida, just for starters.
Now about those scientific names. The family name, Cyperaceae, is based on a representative genus from the family, Cyperus, which is the ancient Greek name for sedge (Dave’s Botanary). I thought maybe the Greek island Cyprus was named for the sedge, but the writers of the wikipedia article on Cyprus think otherwise, that the name is based on the Mediterranean cypress tree, or the henna plant (kýpros), or even an early word for copper. Nevertheless, thinking about that Greek island, Cyprus, will help me remember the family name of sedges: Cyperaceae.
Its Name, Rhynchospora, means Beak-Seed
The genus name, Rhynchospora (pronounced RIN-koh-SPOR-uh), comes form the Greek rhynchus, which means beak, and spora, which means seed (Dave’s Botanary). The beak is on the achene of the flower, and here’s where we start understanding the parts of the flower in grasses and sedges. The achene is what is left of the style. The style connects the pollen-receiving part of the flower (the stigma) with the ovary.
I found good, copyrighted illustrations of these parts in Michener’s Graminoids. Here’s his labeled part of Rhynchospora alba, the White Beak-sedge, used with permission.
The White Tops are Bracts
The flower is a dense cluster of small spikes, sitting within long, white bracts. The bracts look like leaves, but the leaves are actually found at the base of the plant (wikipedia).
Rhynchospora is a sedge that doesn’t always have edges
The so-called “true” sedges of the family Cyperaceae are in the genus Carex, and these plants do have triangular stems – edges. But many of the species of Rhynchospora have round stems, and thus one of the common names for this Rhynchospora colorata is “White-Topped Rush.” Michener points out that the real, identifying characteristic of the family is a “single empty scale below each flower,” but, of course, it’s “… a lot easier to feel triangular stems with your fingers than it is to see one or two subtending flower scales….”
I’ll end with a quote from the site that first identified the White-topped Sedge for me.
Unlike most grass-like plants, this sedge is insect-pollinated and has developed showy white colorization on the bracts that surround its cluster of flowers in each head. The edges of the white bleed into the green color so it looks like Mother Nature spray-painted the white as an afterthought.
The previous owner of our house had sodded this sloping area right to the waterline. It was difficult to mow, so one of the first gardening projects I did when we moved in was to remove the grass and replace it with ferns, Rain Lilies (Zephyranthes atamasco) and this White-Topped Sedge for a more natural shoreline. Other water-loving volunteers such as Bushy Seed Boxes (Ludwigia spp), rushes, and other sedges have joined my transplants.
After two years, this end of the pond looks great, especially during the several months when the white-topped sedge is blooming. This natural bank is also easy to maintain and it provides good habitat for our frogs and other critters.
Sounds perfect for the rocky slopes around here!
