Plant of the Month: Slough Sedge
Our mild Pacific Northwest winters mean there are numerous plants that stay green year-around and they’re not all conifers. This month’s plant could easily be mistaken for some kind of grass, which it resembles at first glance. I’m talking about slough sedge, Carex obnupta.
If you’ve visited a wetland almost anywhere on the west side of the Cascades you’ve likely seen slough sedge. It’s one of our most common sedges, growing in wet places throughout our region. Field Guide to the Sedges of the Pacific Northwest says its “yellowish green, arching, evergreen leaves can be identified from a moving car.” Those leaves are tough, somewhat leathery, 3-7mm (1/10 to ¼ inch) wide, with sharp prickles on the edges of the leaves pointed toward the tip. You’ll definitely notice them if you run your finger down the edge of a leaf.
Slough sedge holds onto its seed-bearing perigynia through the winter. Seeds can then be dispersed during spring floods. The perigynia are the long, fuzzy-looking brown things you see on the plants in the winter. They’re the remains of the female flowers.
Sedges all have specialized flower parts with their own names. It takes more study than I’ve put in to fully understand all the terminology. For now, you can just remember that Carex have separate male and female flowers, often on the same plant. Like other flowering plants, parts of the female flowers mature into seeds. In sedges they’re called achenes, which are enclosed in a perigynium. Perigynia is the plural form.
Carex obnupta spreads by rhizomes, underground runners. Like many other rhizomatous plants, that means that it can become invasive, particularly on small sites. That’s one reason we decided not to plant at the edge of my mother-in-law’s pond garden. We’d rather have more diversity.
Slough sedge is often the dominant species in a wetland. Not many animals eat it because the edges of the leaves are sharp enough to cut skin.
To learn more about Carex obnupta and the many other sedges in the Pacific Northwest, the book to own is Field Guide to the Sedges of the Pacific Northwest. It’s thorough, beautifully illustrated, and as easy to use as any volume on this challenging genus.