Excerpts from Jim Conrad's
from the the September 20, 2009 Newsletter, issued from the Siskiyou Mountains west of Grants Pass, Oregon:
THE POND'S SEDGY BANKS
Much of the pond above my trailer is attractively bordered with a lush, dense, thigh-high mantle of grasslike growth, a small part of which is shown above. You look in vain for grass inflorescences or fruiting heads rising above the arching blades, but if you part the blades, inside them at mid-level you'll indeed find inflorescences, two of which are shown below:
You might recognize these as being produced by a kind of sedge, genus Carex, which are not members of the Grass Family, but rather of the big Sedge Family. If you've looked into sedges probably you know that there's a lot of them, and that they can be a challenge to identify. In the Manual of Vascular Plants of Northeastern United States and Adjacent Canada, 1991 edition, Carex is the largest of all genera, embracing 230 species, and it's a similarly sedgy situation here in the Northwest.
In the above photo the flower arrangement is typical. Male flowers are restricted to three or so slender, silvery flower spikes at the inflorescence top, while female flowers are spirally arranged in much thicker, brown spikes below the male ones. A close-up of a spike of female flowers, showing sharp bracts beneath each sac-like, teardrop-shaped item (the perigynium), is below:
Each perigynium is mostly filled with empty air, but inside and at the bottom of each there's a tiny, three-angled fruit of the achene type (dry, single seeded fruit not splitting at maturity), as shown below:
That achene is topped by a slender, more or less persistent style, which is the "neck" connecting the former ovary with its pollen-collecting stigma, which protruded through the perigynium's open, chimney-like "neck."
You can imagine how such perigynia function. They fall off the flowering stalk, land in water, and float to a distant shore. There they decay or are torn open by a duck or something, and next spring the achene that floated inside it germinates to form a new sedge.
This particular sedge keys out fairly easily to CAREX VESICARIA. Most sedges are so poorly known that they bear no common name, but at least the USDA suggests the name of Blister Sedge for it, though I wonder where the blisters are.
The species is native to most of North America, except for the US Southeast and south-central states, plus it's known as well from parts of Eurasia. You can see yourself what an excellent job this plant does protecting the pond's banks from wave erosion, plus those tiny achenes must be good eating for small birds and rodents.