46. Boechera horizontalis (Greene) Windham & Al-Shehbaz, Harvard Pap. Bot. 11: 266. 2007; Arabis horizontalis Greene, Leafl. Bot. Observ. Crit. 2: 74. 1910; A. suffrutescens S. Watson var. horizontalis (Greene) Rollins, Res. Stud. State Coll. Wash. 4: 50. 1936. TYPE: United States, Oregon, Oregon. Klamath Co.: Crater Lake, along the trail to the boat landing, 1 Aug 1897, Frederick V. Coville & Elmer I. Applegate 334 (holotype, US!; isotypes, RM!, US!).
Plants long-lived, cespitose perennials, with woody caudices, lacking crowded, persistent leaf bases; apomictic, with spheroid pollen. Stems usually 1 per caudex branch, somewhat elevated on woody bases or arising near ground surface from center of basal rosettes, 1–3.5 dm, lower parts with few short-stalked, 3–6-rayed trichomes 0.1–0.3 mm, upper parts glabrous. Leaves at stem bases narrowly oblanceolate, 1–5 mm wide, entire, ciliate near petiole bases with simple trichomes to 0.4 mm, blade surfaces densely pubescent with short-stalked, 3–6-rayed trichomes 0.1–0.3 mm; cauline leaves 3–13, often concealing stem proximally, the uppermost glabrous, with auricles 0.5–1.5 mm. Inflorescences mostly unbranched, 5–32-flowered; fruiting pedicels 4–11 mm, horizontal to descending, straight or slightly curved downward, glabrous. Flowers divaricate-ascending at anthesis; sepals pubescent; petals lavender to purple, 5–6 ´ 1.5–2.0 mm, glabrous; ovules 40–54 per fruit. Fruits 2–4 cm ´ 2–3 mm, horizontal or descending, not appressed to rachises, secund, straight, with slight undulate (non-parallel) edges, glabrous; style 0.2–0.5 mm. Seeds uniseriate, 2.0–2.5 ´ 1.7–2.0 mm; wing continuous, 0.5–1.0 mm wide.
Habitat: dry pumice slopes.
Distribution: United States (Oregon/vicinity of Crater Lake).
Reproductive mode: apomictic triploid.