13b. var. pectinacea
Spikelets appressed to the inflorescence branches or nearly
so. 2n=60. July–October.
Common nearly throughout the state (U.S., Mexico, Central America, Caribbean Islands). Banks of streams and rivers, margins of ponds and
lakes, edges of bottomland forests, and less commonly upland prairies and
glades, often in sandy soil; also fallow fields, old fields, levees, ditches,
roadsides, railroads, and open, disturbed areas.
A single, recent collection from a highly disturbed site in
the Sikeston area (Scott County) is atypical in its growth form and size in
that the plants have more stems that are stouter and somewhat longer than those
of other materials from Missouri. This collection is unusual both in its
robustness and that it might be confused as a perennial because of the
stoutness of the stem bases (however, the plants lack evidence of previous
years’ growth or hardened bases). It matches materials from Louisiana and Texas that were originally determined as E. diffusa Buckley, which Koch (1974)
treated as a synonym of E. pectinacea. The location of the population in
a highly disturbed habitat within an urban area suggests that it may represent
plants introduced from seeds originating farther south in the distribution of
the species. It may be that these plants should be recognized as a separate
variety, but more detailed research is necessary to test this idea.