After writing the above, I remembered a project I supervised a few years ago in which Andrew Gardner, an ambitious undergraduate at that time and now an equally ambitious graduate student, took outstanding photos of 37 Carex spp., including both field photos and diagnostic photos of perigynium, leaf, achene, and other characters. The field photos especially may be helpful as you consider what species to look at:

http://www.botany.wisc.edu/herbarium/carex/

Your friend Carex sprengelii shows up here: http://128.104.26.120/herbarium/carex/db/speciesdetail.asp?species=carspr

Thanks again for your question, and good luck in your work.

Andrew

I often run into this question, and I’ve grown a handful of sedges over the years. Truth be told, I think they’re lovely all year ’round, but I have a sedge bias. In upland, lawnish situations, sedges tend not to be great competitors. Carex sprengelii is a good one because it’s robust, makes big husky clumps and has outstanding inflorescences (the perigynia look like little volumetric flasks at maturity, very striking), and late in the season it often gets a funny broken-leaf look that I like. It’s short-rhizomatous, so it won’t do much spreading, but it will spread by seed. I’ve had a clump growing at the edge of a quasi-rain garden for ca. 8 years and it has spread a bit and looks pretty nice. Carex gracillima and C. arctata also stand a chance in these habitats (C. gracillima is the more common of the two, a real tramp of the woods), and I bet C. hirtifolia or C. jamesii would do well also, though I’ve never seen anyone grow it in that situation. If you have a bit of moisture, some of the other wetland sedges are going to compete relatively well and look pretty: Carex muskingumensis (there are some nice photos on our Lifedesks site): http://vignea.lifedesks.org/image_gallery/45, C. lupulina, C. grayi, and C. intumescens will all do well in wet soils with shade to partial sun, and they’ll probably do fine in upland soils if you water them enough. Sedges are nice b/c they’re so hearty.

In more upland soils, Carex pensylvanica is a real spreader. In sandy soils, C. siccata can be lovely and form a sod. We once had to decommission a trail on a sandy moraine (almost pure sand and gravel) at the UW Madison Arboretum, and C. siccata filled in handily beginning the very next season.

Please let me know if you have questions on this. I have written a paper on the habitats of many of the region’s sedges that might be of interest to you:

http://redwood.mortonarb.org/lab_pages/hipp/publications/Hipp1998_TransWiAcad86_prairieWoodlandSedges.pdf

Good luck, and have fun. Sedges are a blast. Carex is the most species-rich genus of the temperate zone, with about 2000 spp. worldwide, and it’s essential to restoration of woodlands, wetlands, prairies, fens, and a wide range of other habitats.

Take care, and thanks for your question.
Andrew