CESKA, ADOLF* AND OLDRISKA CESKA. Conservation Data Centre, British Columbia Ministry of Environment, P.O. Box 9344, Victoria, BC, Canada V8W 9M1. - Isoetes minima A.A. Eaton (Isoetaceae) - an overlooked terrestrial quillwort of the Pacific Northwest.
Isoetes minima was described from a single collection made by
Wilhelm Suksdorf from Spangle near Spokane, WA, and until recently,
the only authentic material of this taxon has been the type specimen.
On the same collecting trip, Suksdorf collected copious material of
Isoetes howellii that looked superficially the same as the type
of I. minima. Based on this limited material, N.E. Pfeiffer
reduced I. minima into a variety of I. howellii. The
Flora of North America followed Pfeiffer and redefined this variety to
include any small plants of I. howellii with small megaspores.
Several years ago, we found several large populations of I.
minima in Wenatchee Mountains, WA, and in 1996 this species was
also found in south-central British Columbia. Isoetes minima
differs from I. howellii by having small, spiny megaspores and
by sporangia that completely lack velum. Ecologically, I.
minima occupies the most extreme habitats among the western North
American terrestrial Isoetes species. It grows in periodically
wet depressions in Artemisia tridentata sagebrush with
Hesperichon pumilus, Lewisia pygmea, and Floerkea
proserpinacoides as accompanying species.
Key words: Isoetes minima, Pacific Northwest, Pteridophyta