Lepidium didymum L. (syn. Coronopus didymus), lesser swine cress, swine wartcress. Annual, taprooted, in range often rosetted, several—many–stemmed at base, matlike with basal branches radiating in all directions, prostrate to decumbent (ascending), 5—18(—50) cm tall; shoots nearly glabrous, the hairs unbranched, ± foul–smelling from yellowish myrosin cells (sulphur–containing chemicals; visible on fresh materials at high magnification).
Stems cylindric, to 4 mm in diameter, green to purplish.
Leaves helically alternate, < 50—130 mm long, pinnately dissected with several—15 lobes, the lobes further divided or not, petiolate to subsessile, without stipules; petiole hemi–cylindric to U–shaped in ×–section, to 45 mm long, typically with several long hairs on each edge near base; blade oblong to ovate, primary lobes alternate to subopposite, asymmetric, to 15 mm long, ultimate lobes elliptic to oblong, acute at tips but initially with 1—several hairs on tip, pinnately veined, glabrous.
Inflorescence raceme, probably axillary but often appearing opposite a leaf with a new stem forming between them, 10—70 mm long, > 40–flowered, flat–topped with open flowers overtopping buds, lacking bracts; axis glabrous or with some unbranched hairs, sometimes purplish; pedicel ascending, slender, at anthesis 1—1.5 mm long increasing 2× and spreading in fruit.
Flower bisexual, slightly bilateral, ca. 1 mm across, nonshowy; sepals 4, cupped–ovate, 0.6—0.8 mm long, green with narrow membranous margins, sometimes aging purplish at tip, glabrous to sparsely hairy with 1 sepal having 1—several ascending hairs in bud, abscising during fruit development; petals 0(4), if present 0.8 × 0.4 mm, white, lacking claw; stamens 2 fertile (opposite sepals and ovary septum), 4 sterile (lacking anthers) with 2 flanking each fertile stamen; filaments arched, 0.3—0.4 mm long, whitish, of fertile stamens bulbous at base and strongly arched toward stigma, of sterile stamens narrowly triangular and ascending; anthers basifixed, dithecal, ± 0.15 mm long, pale yellow, longitudinally dehiscent; pollen pale yellow; nectaries absent; pistil 1; ovary superior, distinctly 2–lobed, to 0.5 mm long, cordate at base and notched at tip, compressed ⊥ septum, green, glabrous, surface becoming somewhat beaded, 2–chambered, each chamber with 1 ovule; style absent; stigma within notch, ca. 0.25 mm diameter, papillate.
Fruit siliqua (silicle), schizocarpic, compressed and deeply 2–lobed, 1.7—2 mm × 3 mm × 1.2 mm thick, splitting apart from septum into 2 D–shaped, 1–seeded segments, segment surfaces initially beaded but becoming netlike as cells dry.
A. C. Gibson & B. A. Prigge