Thursday, July 11, 2013
Sedges have edges and rushes are round;
Grasses are hollow straight up from the ground.
--botanical memory device
This curious little couplet speaks to the differences found among three similar plant groups: the sedges, the rushes, and the grasses. Their members can easily be confused, unless closely examined. This week’s Mystery plant is a sedge.
Sedges are grass-like plants, belonging to the family called Cyperaceae. Their stems tend to be triangular in cross-section, although there are plenty of exceptional cases, in which the stems may be round. “Rushes” are members of the genus Juncus, whose stems are indeed round in cross-section, and usually solid. Grasses, of course, belong to the enormous family Poaceae, and their stems are indeed hollow, usually, except at the nodes. Back to the sedges, though.
Sedges, as a group, are made up of about 75 different genera, and there are probably between 4000 and 5000 different species. They are found nearly worldwide, in a variety of ecosystems. Economically important sedges include the Papyrus plant from which Egyptians made paper, and delicious water-chestnuts, which are the underground parts of an Asian species. There are also some pretty ones that are grown for ornament. Although the sedge family is a large and very diverse one, it is relatively unimportant in terms of modern human economy. On the other hand, there are plenty of sedges that behave as serious weeds, and so have developed a kind of negative importance. (“Nut-grass” is one of these.) In addition to having more-or-less triangular stems, all sedges are characterized by sheathing leaves whose bases completely wrap around the stem, and by tiny flowers, almost always separated into male and female blossoms, and in different places on the same plant. Sedge’s fruits are hard, little achenes, each one containing a single seed.
Our Mystery sedge is a member of surely the largest genus in the family, with easily 2000 different species. (I’ll go ahead and tell you that this genus is Carex.) Now, members of the genus Carex are characterized by having their female flowers wrapped up in a little green, bulging bag. The little bag is called a “perigynium,” and this is a feature found in no other sedges. You can easily recognize the female, or pistillate spikes. They are the ones that look sort of spiky and bristly, and there are several of them on a single stem. The male, or staminate flowers, in this case, form a single, slender spike, which is found at the top of the flowering stem. This species of Carex forms dense clumps. It’s a handsome species, occurring most often in damp, somewhat shady woods, and it is commonly found all over the eastern USA.
Botanists generally consider the genus Carex to be one of the toughest to deal with, in that there are so many species, distinguished by very “minor” details. For this reason, the various species, which to the casual observer all look practically the same, don’t have a lot of special common names applied to them. Who would like to come up with one for our Mystery Plant?
[Answer: "Sedge,” Carex lurida]
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 firstname.lastname@example.org.
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