Hi everyone! I thought I'd start cross-posting some EDRR info from our program's internal discussions so everyone here can be initiated to some greater weeds of interest. Hopefully this project will help generate more accurate distribution information for the species discussed. I'll try to post according to phenology and what may currently be in bloom. Let me know if you'd like a deep dive on a weed of interest to you not mentioned here. First up, an increasingly used landscape sedge that may follow the trajectory of Carex pendula...

Grassland sedge or Carex divulsa subsp. leersii

Often also referred to as solely Carex divulsa or Carex leersii (feel free to ask any questions in the comments for more taxonomic clarity)

An introduced, understory-dominant invasive sedge found (by Peter Zika) thus far in King County. Sounds similar to Carex pendula but harder to differentiate from local, similar Carex species due to its inconspicuous, diminutive stature. Grassland sedge is escaping plantings and most likely early within its lag phase on the invasion curve in King County. From the 2019 update to the Flora of Oregon, Volume 1:

Carex divulsa Stokes, Grassland Sedge, is a European species commonly planted around buildings and in constructed swales for rainwater control. A prolific seeder, it readily escapes. Now it has been found escaped in the Portland area. It may well become a problem weed in wildlands; some escaped populations in California are now understory dominants in coastal forests.

Unfortunately, Carex divulsa is usually planted by people who want to plant a native ground cover and request native Carex tumulicola. The names have been confused in the horticultural trade. Both species can grow in grasslands and have androgynous spikes and perigynia about 3.5-5.5 mm long. Carex divulsa is a much leafier plant.

16' Inflorescence elongate, the lower spikes remote to overlapping but easily distinguished; perigynia brown to tan, sometimes with narrow green margins, not darker over the achene
16.5. Lower spikes crowded, lowest internodes shorter than to less than 2 times as long as the lowest spike; perigynia 1.5-2 mm wide, beak not winged; plants short-rhizomatous ................................... Carex tumulicola

16.5' Lower spikes remote, lowest internodes more than 2 times as long as the lowest spike; perigynia 2-2.6 mm wide; beak more or less winged; plants cespitose ........................................................... Carex divulsa

Here is an example of Grassland sedge escaping cultivation on UW main campus as noted by Burke Herbarium research associate, Peter Zika.

Here is the Herbarium voucher for the above observation.

Here are the King County observations thus far from iNat (much thanks to Scott Martin (@scottrobmartin) at UW for tracking a few of these)

We could all use more Herbaria records for grassland sedge in WA to get a better sense of its potential impacts locally.

Additional helpful links:

A great worksheet to help differentiate Carex divulsa from Carex tumulicola provided by the City of Portland Parks and Recreation and Environmental Services.

An Exotic non-Grass Graminoids of Potential Concern powerpoint presentation by Dominic Maze from City of Portland Environmental Services with good diagnostic ID for Carex divulsa.

A list of banned landscape plants within the City of Eugene, Oregon, where Carex divulsa is included alongside some of the PNW's most troublesome & highly regulated weeds.

A couple Seattle landscape architecture projects where Carex divulsa itself (and not mistakenly as Carex tumulicola) has been specified for installation. One will be in Queen Anne, the other in Eastlake.

Posted on May 6, 2022 06:00 PM by