Oenothera heterophylla Spach. subsp. heterophylla, variable evening primrose. Annual (perennial herb), taprooted, 1–stemmed at base, ± rosetted, branched above midplant, in range to 35 cm tall; shoots with basal leaves and cauline leaves, with long hairs, the longest ones with swollen bases (pustulate).
Stems ± cylindric, < 4 mm diameter, with low ridge descending from leaf. tough; green or purple–red aging brownish, strigose and short–strigose with upward–pointing hairs.
Leaves helically alternate, simple, petiolate (basal leaves) and sessile (cauline leaves), without stipules; petiole < 5 mm long; blades obovate (rosette leaves) or narrowly elliptic to lanceolate or narrowly ovate, < 15—90 × 3—17 mm, tapered at base, irregularly low–dentate, acute to tip, pinnately veined with principal veins raised on lower surface.
Inflorescence leafy spike, of axillary flowers (alternatively interpreted as solitary axillary flowers), with nonglandular hairs and scattered glandular hairs on green tissues.
Flower bisexual, radial, ca. 35 mm across; hypanthium cylindric funnel–shaped at top, to 22 mm long, cylindric portion ca. 1.3 mm diameter, light yellow, lined with erect short hairs; sepals 4, partially fused splitting from pressure of expanding petals along 2 suture line upward from base but remaining coherent approaching tip, with green, subterminal tips 3 mm long, mottled red and green, outer surface with scattered long hairs (pustulate) and stalked glandular hairs; petals 4, widely spreading, rhombate, ca. 18 × 13 mm, light yellow, acute at tip; stamens 8 in 1 whorl, attached on rim of hypanthium; filaments, exserted, ca. 15 × 0.2 mm, light yellow; anthers dorsifixed, dithecal, (3.4—)4—5.5 mm long, light yellow, longitudinally dehiscent; pollen light yellow, pollen grains held in a mass by minute threads (viscin threads); nectary at base of hypanthium surrounding style base, 1.5 mm long; pistil 1; ovary inferior, ± cylindric, (inconspicuously 4–sided), to 10 × 1—1.2 mm, with ascending long hairs and stalked glandular hairs, 4–chambered, each chamber with many ovules; style exserted, ± 40 mm long, green within hypanthium and green–yellow where exposed; stigma lobes above tips of anthers, horizontal and widely spreading, fingerlike, in range 3—4 mm long, green, sticky.
Fruit capsule, 4–valved, many–seeded, ± cylindric, in range 20—25 × 4 mm, curved at base, having 4 thick lobes at top, with long ascending hairs and stalked glandular hairs; in chamber seeds oriented upward in each chamber.
Seed angular fusiform, 0.9—1.1 × 0.3—0.4 mm, light brown.
A. C. Gibson