Japanese name: メリケンムグラ Scientific name:Diodia virginiana
[Overview]
An annual found on rice paddy ridges, in abandoned paddies, and in slightly moist places on riverbanks.
When emergent to submerged, it may become a perennial.
The stems are 10–80 cm long, branch at the base, and spread in all directions in a mat.
The stem is square in cross section, with downward-pointing hairs on the ridges.
Roots emerge from the leaf axils of stems that touch the ground.
The leaves are simple and opposite, elliptic to broadly linear, 3–6 cm long and 0.5–1 cm wide.
The leaf surface is slightly glossy.
The leaf margins have short stiff hairs and are rough.
The opposite stipules fuse into a semicircle that is deeply cleft, with spiny lobe tips.
The petiole is 1–2 mm.
The flowers are white and borne singly in the leaf axils.
The corolla is tubular, 9–11 mm across and 8–11 mm long, with 4 lobes at the tip, and is densely hairy inside and on the margin.
The fruit is a schizocarp that forms in pairs and is often dispersed by floating on water.
[History]
It is naturalized in temperate Asia.
In Japan it was discovered in Okayama in 1969.
