Monday, March 21, 2011

Carex divulsa – the un-Berkeley sedge, invasive in California

Once upon a time, California native plant horticultural enthusiasts offered Berkeley sedge (Carex tumulicola Mackenzie, Section Phaestoglochin Dumortier) in the California trade. Sedges, being a perhaps the most speciose natural genus of angiosperms (perhaps 2000 species), are confused, is confusing, and confuse. Whence, a transposition occurred: Carex divulsa Stokes (also of Sect. Phaestoglochin), but native to Eurasia, was somehow conflated in the horticultural trade with C. tumulocola. The result: Carex divulsa is now sold widely: in California easily obtained, used frequently in "native" or "xeric" or "drought resistant" landscape plantings.

Carex divulsa, at least in mesic, coastal central California, is thus established. The photograph is of a seeding, one of many, that volunteered on the periphery of a C. divulsa purchased at a generic-grade garden center of a major hardware retailer (names withheld to protect the innocent).

Carex divulsa is neither xeric nor native. Its ecological preference in its native range is as a moderate to obligate mesophyte or subhydrophyte.

Carex divulsa will be spreading in Californa. One only has to visit the planting beds in the vicinity of the UC Santa Cruz Science Library to witness this: these plants are now, perhaps 8 yr after coming out of a 1-gallon can, clumps to 2 feet diameter and spreading babies about with abject rapaciousness.

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