Arabis serotina E. S. Steele, Contr. U.S. Natl. Herb. 13: 365. 1911

Biennials; short-lived; sexual; caudex not evident. Stems usually 1 per plant, arising from center of rosette near ground surface, 4-10 dm, glabrous throughout. Basal leaves: blade obovate to oblanceolate, 5-20 mm wide, margins dentate, not ciliate, surfaces glabrous or subapically puberulent, trichomes simple, 0.1-0.2 mm. Cauline leaves: 30-80, not concealing stem; blade auricles absent, surfaces of distalmost leaves glabrous. Racemes 70-150-flowered, multi-branched. Fruiting pedicels divaricate-ascending to horizontal, straight or gently recurved, 6-15 mm, glabrous. Flowers divaricate-ascending at anthesis; sepals glabrous; petals white, 2.8-4 × 0.6-1 mm, glabrous; pollen ellipsoid. Fruits divaricate-ascending to widely pendent, not appressed to rachis, not secund, straight or slightly curved, edges parallel, 4.3-7.9 cm × 1.5-1.8 mm; valves glabrous; ovules 30-42 per ovary; style 0.1-0.2 mm. Seeds uniseriate, 1.2-1.7 × 0.7-1 mm; wing continuous or, sometimes, distal (rarely absent), 0.1-0.2 mm wide. 2n = 14. Flowering Jul-Sep. Shale barrens and wooded slopes of crumbling shale; of conservation concern; 100-500 m; Va., W.Va.

Boechera serotina is unique among members of the genus in its highly branched inflorescences and late (summer-fall) anthesis. It is in the Center for Plant Conservation’s National Collection of Endangered Plants.