Oenothera triloba Nutt., stemless evening primrose, three–lobed primrose. Annual, taprooted, 1–stemmed at base, flat–rosetted, acaulous, < 10 cm tall; shoots with only basal leaves to 180 mm long, short–strigose with upward–pointing hairs; taproot fleshy, white surrounded by pink phloem and cortex.
Stem short and concealed by petioles of basal leaves.
Leaves helically alternate, irregularly pinnately lobed, cut, petiolate, without stipules; petiole compressed top–to–bottom, to 60 mm long, fleshy and indistinct from blade with narrow, green wings and short, narrow lobes and teeth, rose–red at base and paler approaching blade; blade oblong to oblanceolate, terminal lobe lanceolate, to 35 × 20 mm, toothed and with or without sublobes, midlobes asymmetric and < 25 mm long, toothed and crisped, the lowest lobes linear to threadlike, formed along channeled, white midrib rounded and fleshy on lower surface.
Inflorescence leafy spike, compact and terminal, of helically alternate, axillary flowers.
Flower bisexual, radial, 50—55 mm across, to 120 mm long; hypanthium above ovary forming a long floral tube, tube sharply 4–angled and 4–sided (square), to 97 × ± 2 mm with terminal portion expanded and narrowly funnel–shaped to 5 mm wide at orifice, cream–colored aging rose, sparsely short–strigose with upward–pointing hairs and scattered longer, glandular hairs, thick–walled most of length, upper portion lined with short papillae and several long–based hairs; nectary at the base of hypanthium surrounding style base, with copious nectar; sepals 4, partially fused but free at tip 1.5—2.5 mm, ca. 42 mm long, pale green with fine pink midstripes, splitting from pressure of expanding petals along 1 suture line, splitting with 4 sepals as unit reflexed them spreading, short–strigose with upward–pointing hairs and scattered, longer red hairs, each sepal 4—4.5 mm wide with raised midvein, inner surface yellowish; petals 4, spreading ⊥ from rim of hypanthium, fan–shaped, 26—32 × 25—31 mm, light yellow aging reddish, palmately veined with 3 principal veins at base; stamens 4 in 1 whorl, arising from rim of hypanthium, monomorphic, exserted; filaments ascending, < 15—19 mm long, light yellow, somewhat S–shaped at base and narrow at top; anthers versatile, dithecal, 10—12 mm long, light yellow, longitudinally dehiscent; pollen light yellow, pollen grains 3–pointed, held in mass by minute threads (viscin threads); pistil 1; ovary inferior, ± 4–sided with irregular ridges, ca. 5.5 × 3.5 mm, rose–red, with dense patches of short–strigose hairs along ridges and long hairs with red, exaggerated, fingerlike bases, 4–chambered, each chamber with stack of many ovules; style to 115 mm long + stigma lobes, axis straight and 0.6 mm diameter, white, glabrous, stigmatic lobes divergent–spreading, exserted to 22 from hypanthium and 4—5 mm above the level of the highest versatile anther, not straight, 4—5.3 × 0.6—0.85 mm (variable), yellow to yellow–green, papillate and sticky.
Fruit capsule, loculicidal, 4–winged, 70+–seeded, ± obovoid compressed top–to–bottom, ca. 25 × 10 × 5—6 mm, wings mostly < 3 mm wide decreasing to absent at base, with 4 ascending to spreading lobes at top alternating with wings, lobes triangular, ± 5 × 3 mm, short–strigose with some scattered long hairs.
Seed angular club–shaped to oblique wedge–shaped, to 3.3 × 1.6 mm, brown, narrowly winged along 1 edge and approaching top, with basal hilum, faces with domed cells (minutely beaded).
A. C. Gibson