The photo above shows a close-up of the inflorescence of closeflowered knotweed as seen in shallow alkaline basins along the old highway to the southwest of Fishtrap Lake in eastern Washington.........May 30, 2008. Note the numerous bracts with white-winged margins within each inflorescence.
Closeflowered knotweed is a small annual, smooth-surfaced with a simple or many-branched stem from 6-20 cm high. The leaves are linear (See photos.), 1-3 cm long and 1-2 mm wide. The flowers are 2-4 per node in crowded clusters at the ends of the branches, or occasionally in the axils of the leaves. The leaves become reduced to small bracts near the ends of the branches. The terminal bracts are distinctly white-margined (See photo below.).
The flowers are 1.5-2.5 mm long with greenish midstripe and white to pinkish borders. There are 8 stamens, with the 3 inner ones bearing anthers, the other 5 without anthers. Closeflowered knotweed is very similar to (and probably closely related) Kellogg's knotweed (Polygonum kellogii) but may be separated from the latter which has few or no bracts among the flowers that are white margined, and are usually less than 7 cm high.
Closeflowered knotweed may be found in grassy areas or vernal pools or on dry open ground.
Closeflowered knotweed may be found east of the Cascade Mts. from Kittitas County, Washington south to California and east to Idaho and central Montana.