Vascular Plants of Williamson County

Lepidium austrinum [Brassicaceae]
southern pepperweed

Lepidium austrinum Small, southern pepperweed. Annual, taprooted, initially rosetted, 1–stemmed at base, initially unbranched with diverging lateral branches in canopy, aging with lateral branches nearly to base, erect, in range 7—50 cm tall; shoots with basal leaves and cauline leaves, all leaves petiolate, hirsute, to 1.5 mm long.

Stems

Stems cylindric, to 3 mm diameter, straight, internodes to 25 mm long, hirsute hairs ″ radiating.

Leaves

Leaves helically alternate, pinnately lobed to serrate, petiolate, without stipules; petiole channeled, to 25 mm long (pinnately lobed leaves) decreasing upward; blade to 60 mm long, oblanceolate in outline, of lobed leaves with to 8 alternate, spreading lateral lobes, terminal lobe > lateral lobes, unlobed leaves oblanceolate or obovate to elliptic or lanceolate, < 15—40 × 4—15 mm, thin, serrate on margins, pinnately veined with principal veins slightly raised on lower surface.

Inflorescence

Inflorescence raceme or panicle of racemes, terminal, many–flowered, flat–topped and ca. 4 mm across at top, flowers helically alternate, mostly lacking bracts; peduncle to 5 mm long; bract subtending raceme leaflike, oblanceolate–linear, subsessile, to 10 × 1 mm, entire or with small tooth on margin, acute at tip, 1–veined raised on lower surface, short–hairs on lower surface and along margin to midblade; rachis somewhat ridge, ridge descending from each pedicel, with short arched hairs; pedicel ascending, cylindric, ca. 2 mm long, with short arched hairs on upper side.

Flower

Flower bisexual, bilateral, 1 mm across; sepals 4, dimorphic, 1 opposite on flat sides of ovary, cupped–ovate, pair opposite edges of ovary cupped over edges of ovary, 0.7—0.95 mm long, green with membranous margins, inner sepal sometimes with several hairs; petals 4, spatulate to obovate, 0.6—0.9 × 0.35—0.4 mm, < sepals, white; stamens 2, free, opposite flat sides of ovary at septum; filaments erect, 1 mm long, white; anthers dorsifixed, dithecal, ± 0.25 mm, light yellow, longitudinally dehiscent; pollen light yellow; pistil 1; ovary superior, flattened ⊥ septum, roundish and slightly notched at top, ca. 1 × 1.1 mm, green, short–ciliate along edges with arched hairs, often with some short hairs on faces to midpoint, 2–chambered, each chamber with 1 ovule; stigma terminal, subsessile in notch at top, notch 0.2—0.5 mm deep, stigma domelike, 0.2—0.25 mm diameter, colorless, papillate.

Fruit

Fruit siliqua (silicle), dehiscent by 2 valved, 2–seeded, broadly elliptic with notch at tip, in range 2.4—3.2 × 1.8—2.1 mm, not veiny with a midline (septum), notch to 0.5 mm deep, with seeds attached at the top to an elliptic, translucent septum; not beaked; pedicel in fruit cylindric.

Seed

Seed compressed–elliptic with folded embryo evident, in range ± 1.5 × 0.8 mm, dull cinnamon brown, gelatinous when wetted.

A. C. Gibson