1. Heteranthera dubia (Jacq.) MacMill. (water star‑grass)
Pl. 189 g, h; Map 674
Zosterella
dubia (Jacq.) Small
Plants
perennial. Stems elongate. Leaves mostly alternate, to 15 cm long, 2–5 mm wide,
all linear, tapering basally and lacking a petiole, the tip acuminate. Flowers
single, sessile in the leaf axils. Perianth yellow, actinomorphic, the tube
elongate, 15–70(–120) mm long, the lobes linear to linear‑lanceolate,
5–12 mm long. Stamens all the same length, the filaments glabrous. 2n=30.
June–September.
Common
in the Ozark and Ozark Border Divisions, sporadic north of the Missouri River (U.S., Mexico, Guatemala, Cuba). Submerged or floating‑leaved aquatics in streams, rivers,
spring branches, sloughs, rarely along lake margins, frequently rooting in mud.
This
species often forms large, leafy, submerged masses in the cool, fast‑flowing
waters of streams and spring branches in the Ozarks. However, it can also be
found in warmer, more sluggish waters. Flowering occurs mostly in quiet
backwaters or in situations where the plants colonize muddy banks. The species
can also produce cleistogamous flowers that are entirely enclosed in the
spathes. It provides food for waterfowl and mammals, which sometimes eat the
foliage.
Many
botanists separate this species into its own genus, Zosterella (Horn,
1985), based on details of its flowers and inflorescence structure and its
monomorphic leaves. Rosatti (1987) has discussed reasons for maintaining it in Heteranthera.
Sterile, submerged plants are sometimes mistaken for a Potamogeton, but
leaves of H. dubia can be distinguished by the lack of a well‑defined
midvein.