2. Callitriche palustris L. (vernal water starwort)

C. palustris var. verna (L.) Fenley ex Jeps.

C. verna L.

Map 2195

Stems 10–30 cm long, prostrate to ascending. Leaves 3–20 mm long, polymorphic; the submerged leaves mostly linear, shallowly notched at the tip, 1-nerved, usually grading into the floating leaves; these obovate to spatulate, rounded at the tip, 3(5)-nerved; forming rosettes on the surface of the water (the rosette leaves progressively shorter and more rounded); leaves on stranded plants linear to obovate. Flowers subtended by 2 minute, pale, inflated bracts, these shed before the fruits mature. Fruits 1.1–1.4 mm long, 0.9–1.2 mm wide, sessile, more or less heart-shaped, with the tip more rounded than the base, the nutlets narrowly winged, at least above the midpoint, the basal, unwinged portion appearing somewhat thickened. 2n=20. March–September.

Known thus far from a single site in St. Louis County (northern U.S. south to Virginia, Texas, and California; Alaska, Canada, Greenland, South America, Europe, Asia). Mostly submerged aquatics (stem tips usually with floating leaves) in spring branches.

Missouri specimens of this species were first collected by Bill Summers in 1979, but these were first determined as the closely related C. heterophylla and went unnoticed until recently. Vegetatively, the two species are indistinguishable, although the Missouri specimens of C. palustris collected thus far tend to be relatively robust with a greater proportion of more broadly obovate leaves (this probably due to environmental influences). Callitriche palustris also grows in portions of Nebraska, Iowa, and Illinois, and thus should be searched for elsewhere in northern and eastern Missouri.