Samolus parviflorus Raf. [syn. S. valerandi L. subsp. parviflorus (Raf.) Hultén)], thin–leaf brookweed, water pimpernel. Perennial herb, ± aquatic, fibrous–rooted, rosetted from creeping, slender stem, 1–stemmed from rosette, unbranched or diffusely branched, erect, in range 10—30 cm tall; shoots glabrous; roots adventitious.
Stems cylindric, slender, < 1 mm diameter, wiry.
Leaves helically alternate, simple, petiolate, without stipules; petiole winged grading into blade, to 4 mm long, very short on upper cauline leaves; blade broadly elliptic or oval to obovate or ovate, 12—35 × 6—20 mm, typically tapered at base, entire, obtuse to round at tip (basal leaves) or broadly acute (cauline leaves) at tip, pinnately veined with conspicuous midrib and faint lateral veins.
Inflorescence racemelike (the lowest branch also a short raceme), terminal, thin, ± flat–topped, initially with flowers overtopping buds, several—many–flowered, somewhat delicate, bracteate, glabrous; bract subtending inflorescence leaflike, obovate to ovate; peduncle ca. 10 mm long; rachis conspicuously zigzagged, flexuous, slender, to 100 mm long, internodes 2—7.5 mm long, glossy green, glabrous; bractlet subtending pedicel absent; pedicel ascending, in range 5—6 mm long spreading and increasing to 9 mm long in fruit, with another bractlet at midpoint or lower on pedicel, the bractlet awn–shaped, < 1 mm long, persistent in fruit.
Flower bisexual, radial, 2—3.5 mm across; calyx (4—)5–lobed, green; tube cup–shaped, ± 1.2 mm long; lobes ascending, triangular to deltate, 0.5—0.8 mm long, green with white tip, minutely dotted; corolla (4—)5–lobed, 1—1.3 mm long, white; tube short–cylindric, 0.25 × 0.9—1 mm; lobes ascending like calyx lobes, obtuse–oblong to round–oblong, 0.8—1.2 mm long, ± truncate or slightly notched at tip, with domed cells; stamens 5 fertile stamens (opposite corolla lobes) and 2—5 sterile staminodes fused at sinuses of corolla (opposite calyx lobes); filaments sharply tapered to tip, 0.3—0.4 mm long, white, glabrous; anthers dorsifixed, dithecal, inversely heart–shaped, ca. 0.4 mm long, orange–yellow, longitudinally dehiscent; pollen orange–yellow; staminode fingerlike, 0.5—0.6 mm long, white; pistil 1; ovary ± inferior (two–thirds), fused to calyx tube, hemispheric and truncate, 10–veined, 1–chambered with many ovules attached to center; style ± 0.25 (absent); stigmas (3)5, terminal, slightly lobed, papillate.
Fruit capsule, loculicidal, 5–valved, many–seeded, initially spheroid, when open cup–shaped to bell–shaped, in range 1.5—2.3 mm across, 5 triangular to deltate calyx lobes opposite and partially covering 5 tannish, recurved valves, rarely splitting below midpoint, seeds on basal central post; calyx tube portion of fruit finely 10–ribbed.
Seed 3—5–sided, in range 0.3—0.4 mm long, dull reddish brown to dark brown; seed coat minutely bumpy.
A. C. Gibson