1. Bacopa rotundifolia (Michx.) Wettst. (water hyssop)
Pl. 480 e, f;
Map 2193
Plants annual or
perennial herbs, with fibrous roots, aquatic or sometimes terrestrial when
stranded on mud. Stems (5–)10–60 cm long, at least the lower portion usually
submerged, the apical portion weak and floating on water (occasionally entire
plant floating), when terrestrial then prostrate to loosely ascending, rooting
at the lower nodes, not angled, moderately to densely and finely short- hairy,
at least on newer growth. Leaves opposite, sessile. Leaf blades 1.0–3.5 cm
long, (8–)10–28 mm wide, relatively thick (but drying very thin and fragile),
broadly spatulate to more commonly broadly oval or circular, unlobed, rounded
at the tip, shallowly cordate to rounded or broadly angled at the base, mostly
at least slightly clasping the stem, the margins entire, but sometimes finely
short-hairy, the venation palmate with 5–9 main veins, the surfaces glabrous or
nearly so at maturity, the upper surface somewhat shiny. Inflorescences axillary,
the flowers 1 or 2(–4) per leaf axil, the flower stalks 6–23 mm long; bractlets
absent. Flowers perfect. Calyces 3.0–4.5 mm long at flowering, becoming
enlarged to 4–6 mm at fruiting, deeply 5-lobed nearly to the base, glabrous,
the outer 3 lobes leaflike, ovate to broadly ovate, the inner 2 inconspicuous,
lanceolate. Corollas 4.5–9.0 mm long, not bilabiate, weakly zygomorphic,
5-lobed, glabrous, the tube slightly shorter than to about as long as the
lobes, white or less commonly very pale pinkish-tinged with a yellow throat,
spurless, the throat open, the lobes collectively bell-shaped above the slender
tube, individually oblong-obovate with more or less truncate but shallowly
notched tips. Fertile stamens 4, the filaments of 2 lengths, not exserted, the
anthers attached near their midpoints, the anther sacs parallel; staminodes
absent. Style 1, not exserted, forked near the tip, each branch with an
expanded, irregularly oval, cushionlike stigma at the tip. Fruits capsules,
3.5–5.5 mm long, globose to broadly ellipsoid, glabrous, the 2 locules equal in
size, dehiscent longitudinally by 4 valves. Seeds numerous, 0.4–0.6 mm long,
ellipsoid to cylindric with a minute tail-like appendage at each end, not
flattened, the surface yellowish brown, with a network of fine ridges. 2n=36.
May–September.
Scattered south
of the Missouri River, uncommon farther north (eastern U.S. [except some
northeastern states] west to Idaho and Arizona; Canada; introduced in
California and Asia). Floating or mostly submerged aquatics in shallow water of
ponds, lakes, sinkhole ponds, swamps, and sloughs, less commonly in backwater
areas of streams; also ditches and rice fields; sometimes stranded on wet mud.