Excerpts from Jim Conrad's
from the the July 22, 2012 Newsletter issued from the woods of the Loess Hill Region a few miles east of Natchez, Mississippi, USA
Above you can see a plant characteristic of poorly drained areas such as ditch bottoms, pond edges and wet pastures -- this plant with only its flowering head emerging above floodwater, with a water strider sailing atop the water's surface below it.
This is not a grass -- not a member of the Grass Family, the Poaceae -- but rather it belongs to the Sedge Family, the Cyperaceae. Like the Grass Family, the Sedge Family is a big one, with some 5,500 species in about 109 genera. Many people assume that Sedge Family members are grasses, but there are important differences. The most easily seen distinction between the two families is that grasses typically have stems that are round in cross-section, while stems of members of the Sedge Family normally are triangular. Grass leaves tend to alternate with one another on the stem, but in the Sedge Family they are spirally arranged, in three ranks, not two.
Our plant in the picture belongs to one of the largest and most widely spread genera of the Sedge Family, the genus Cyperus, for which about 600 species are recognized -- about 45 listed for Mississippi. The most famous species of the genus Cyperus is Papyrus of ancient Egyptian paper fame. In Mexico we had the ornamental Umbrella-Plant, also African in origin, which we profile at http://www.backyardnature.net/yucatan/umbrella.htm.
Our flooded Cyperus is CYPERUS VIRENS, in the literatures often called Green Flatsedge. It's native to and common in the American tropics and subtropics, from South America up to the US Deep South, and it's been introduced into California.
The most characteristic feature distinguishing Green Flatsedge from many other Cyperus species is how its numerous flowers are stacked above one another in very flat spikelets (thus the name flatsedge), and the spikelets are gathered in densely spiked heads, as shown below:
That flowering head is inhabited by a surprising community of spiders and insects, apparently seeking refuge from the flooding.
Also, notice that Green Flatsedge's spikelet clusters are grouped at the end of slender stems, called rays, that arise other slender rays. Some other flatsedge species bear similar heads of flat spikelets but their heads are on stems arising directly from the main stem; their inflorescence stems are not branched. Some Green Flatsedge plants even display third-order branching.
Among ecological services provided by the Green Flatsedge is the production of many tiny seeds eaten by small birds and mammals, and the mere fact that it grows robustly, photosynthesizing oxygen for all of us, in places too waterlogged for other plants to grow in.