Ludwigia repens Forst., creeping primrose–willow, creeping water primrose. Aquatic perennial herb, fibrous–rooted, mat–forming, procumbent with ascending to spreading branches from horizontal axes, < 16 cm tall; shoots with cauline leaves, essentially glabrous, not glutinous on young growth; adventitious roots nodal
Stems cylindric, to. 3.5 mm diameter, green wit reddish tinge and short white streaks (crystal aggregates), internodes to 30 mm long.
Leaves opposite decussate, simple, petiolate, with stipules; stipules 2, attached to base of petiole, ± ovate, 0.3—0.4 mm long, not secreting liquid, mostly purplish red, withering; petiole hemicylindric to flattened on upper side, < 5 mm long and indistinct from leaf blade, glabrescent; blade obovate (elliptic), < 10—35+ × 3—19 mm, long–tapered at base, entire or minutely toothed on margins above midblade, acute at tip lacking a small glandular point on the lower surface, cpinnately veined with principal veins slightly raised on lower surfaces, surfaces ± glossy green with narrow reddish margins, glabrous.
Inflorescence flowers solitary and axillary (leafy spike), subsessile, at each node having 1 flower, 2 flowers, or eventually 2 branches, glabrous; pedicel at anthesis < 0.5 mm long increasing to < 1.5 mm long in fruit and constricted at base, with 2 opposite bracteoles at base of ovary, bracteoles oblanceolate–linear to linear with swollen base, at anthesis 3—4.5 × 0.45—0.6 mm increasing slightly in fruit (to 5 × 1 mm in fruit) , green with 2 minute purple–red stipules concealed on inner side ± 0.2 mm long, acuminate at tip, not wet or secreting, ± persistent in fruit.
Flower bisexual, radial, ca. 6 mm across; hypanthium < 0.6 mm long, aging red where petals formerly attached, nectary 4–lobed, yellowish green, glabrous, producing copious nectar on top of ovary; sepals 4, spreading, acute–triangular to deltate, 3 mm long increasing slightly in fruit, green, with 3 parallel veins, glabrous; petals 4, obovate to elliptic, to 3.1 × 1.5—1.8 mm, yellow with raised white midvein, rounded and not shallowly notched at top, glabrous, 1–veined; stamens 4 in 1 whorl, opposite sepals; filaments ± 1.5 mm long, pale green, leaning inward and tapered from base; anthers dorsifixed, dithecal, 0.8—1 mm long, ± cream–colored with broad connective, longitudinally and inwardly dehiscent; pollen white, permanently united in tetrads, sticky and held in a mass by minute threads (viscin threads); pistil 1; ovary inferior, funnel–shaped strongly 4–sided and 4–angled, ca. 1.5 mm long, green, with rib on each face and short hairs curled upward along angles, 4–chambered, each chamber with many small ovules; style < 2 mm long, pale green; stigma at same level as and touching anthers, subspheroid and inconspicuously 4–lobed, ca. 0.6 mm diameter, yellow–green.
Fruit capsule, irregularly dehiscent, many–seeded, bell–shaped and 4–sided, 6—7.5 × 3.5—4 mm, each face with a broad rib, top truncate and 4–lobed but lacking hairs, glabrescent; sepals persistent, erect to ascending or folded over fruit, 3–veined; style abscised.
Seed± ellipsoid, 0.4—0.8 × ± 0.4 mm, tannish.
A. C. Gibson