1. Rotala ramosior (L.) Koehne

R. ramosior var. interior Fernald & Griscom

Pl. 448 c–e; Map 2038

Plants terrestrial or strongly emergent aquatics, annual, fibrous-rooted, sometimes rooting at the lower nodes, not producing offsets at the base, glabrous. Stems 5–40 cm long, erect or strongly ascending, not wandlike, strongly 4-angled (square in cross-section), often branched from near the base, the branches spreading to arched upward, not rooting at the tip. Leaves opposite, sessile, 1–5 cm long, 2–12 mm wide. Leaf blades linear to narrowly lanceolate, narrowly oblong-triangular, or oblanceolate, those of the largest leaves always 3 mm or wider), narrowed or tapered to a usually sharply pointed tip, the lower leaves truncate to more commonly auriculate-cordate at the base, the upper and often also median leaves tapered at the base. Inflorescences of solitary flowers, these sessile or nearly so. Flowers actinomorphic, the hypanthium about as long as wide, cup-shaped to urn-shaped (sometimes becoming nearly globose at fruiting), symmetric at the base (not pouched or spurred), not oblique at the tip, the hypanthium plus sepals 2–5 mm long, with 4 or 8 longitudinal ridges (these best developed at fruiting). Sepals 4, triangular to broadly triangular, the appendages about as long as the sepals, thickened, triangular. Petals 4, 1–2 mm long, white to light pink, not persistent at fruiting. Stamens 4(–6), those of different flowers with filaments the same length, the anthers not exserted, light yellow. Pistils lacking a nectary disc, the ovary incompletely 3- or 4-locular, the style relatively long and exserted (very short elsewhere). Fruits 3–5 mm in diameter, globose to oblong-globose capsules, dehiscing longitudinally along (2)3 or 4 of the partitions between locules, the outer wall with fine transverse lines (best observed with magnification). Seeds numerous, 0.4–0.8 mm long, asymmetrically ovoid (1 side concave, the other convex), the surface with a network of fine, sometimes faint ridges, yellow to reddish brown. 2n=32. June–October.

Scattered widely in the state, most commonly south of the Missouri River (nearly throughout the U.S.; Canada, Mexico to South America, Caribbean Islands). Banks of streams, rivers, and spring branches, margins of ponds, lakes, swamps, and sloughs, and edges of marshes and saline springs; also ditches, fallow fields, crop fields, and open disturbed areas.

Inland plants are slightly more robust than those of coastal areas and have been called var. interior, but Graham (1975) noted that the quantitative differences between the varieties do not merit taxonomic recognition.