Vascular Plants of Williamson County

Oenothera speciosa [Onagraceae]
pink evening primrose, texas primrose, amapola del campo, showy primrose, mexican evening primrose

Oenothera speciosa Nutt., pink evening primrose, texas primrose, amapola del campo, showy primrose, mexican evening primrose. Perennial herb or annual, rhizomatous, rosetted when shoots young, decumbent to ascending, 15—60 cm tall; shoots with basal leaves and cauline leaves, short–strigose sometimes aging glabrescent.


Stems cylindric, to 3 mm diameter, green to ashy gray aging red–purple at base, with persistent, short–projecting leaf bases.


Leaves helically alternate, shallowly pinnately lobed and short–petiolate (basal leaves) and toothed and sessile (cauline leaves), short–petiolate, without stipules; petiole often winged, in range < 5 mm long, wavy on margins; blade broadly elliptic to oblong, 30—60(—90) × 10—25 mm (lower leaves) to lanceolate or narrowly elliptic to ovate, < 10—45 × < 3—22 mm (middle and upper cauline leaves), tapered at base (sometimes cauline leaves with short basal lobes), lobes grading to serrate or dentate and wavy on margins (subentire), acute at tip, pinnately veined with midrib sunken on upper surface and raised on lower surface, white short–strigose.


Inflorescence leafy raceme, terminal, of helically alternate axillary flowers, with pink and rose buds nodding at tip and becoming erect just before anthesis, white short–strigose; bractlet sessile, leaflike, elliptic to narrowly lanceolate, to 12 mm long, formed on projecting base, long–acuminate at tip; axis conspicuously short–strigose; pedicel 1—3 mm long, grading into narrowed ovary base.


Flower bisexual, radial, 25—52 mm across; anthesis at sunset; hypanthium above ovary, narrowly funnel–shaped, 10—13(—15) × 2.5 mm, light greenish but reddish on exposed surface or aging reddish, swollen at base, white short–strigose, internally pubescent to midpoint, nectary at base of hypanthium surrounding style base; sepals 4, partially fused as they split from pressure of expanding petals along suture lines, splitting along 1 suture line base to tip, short–reflexed at base and ascending and appressed to corolla, unit cupped–broadly ovate and 1–sided (= 4–sepal unit), individually narrowly lanceolate to linear, 15—25(—30) × 2.5—3.2 mm, greenish aging pinkish and reddish on margins, acuminately tapered into a cylindric tip, white short–strigose, with an evident midvein and faint, parallel secondary veins, in bud the tips free and spreading, 0.5—1(—4) mm long; petals 4, spreading, forming dish–shaped corolla, slightly unequal, not clawed, fan–shaped to broadly heart–shaped, in range 15—32 × 15—27 mm, pink to purplish pink or rose with yellowish tinge diffusing from thicker (pale pink or white), yellowish green base, palmately veined with rose veins, glabrous; stamens 8 in 1 set, arising as fused ring from hypanthium rim and also barely fused to basal edge of 4 petals, monomorphic; filaments erect, 15—17 mm long, white but yellow at enlarged base, glabrous; anthers exserted, versatile, dithecal, linear, 9—11 mm long, pale yellow, longitudinally dehiscent; pollen pale yellow, pollen grains 3–pointed, held in a mass by minute threads (viscin threads); pistil 1; ovary inferior, club–shaped, to 18 mm long, green, lower portion tapered and obscurely veined, upper portion conspicuously 8–ribbed with 4 being somewhat winglike, strigose, 4–chambered, each chamber packed with many ovules attached to center; style exserted to level of anthers, 30—34+ mm long, white, densely puberulent at base (2 mm); stigma 4–lobed, the lobes spreading, fingerlike, 4—7 mm long, whitish.


Fruit capsule, loculicidal, 4–valved, many–seeded, club–shaped to obovoid, 10—18 mm long, enlarged upper portion conspicuously 8–ribbed, 4 ribs sometimes winglike, dehiscing only in upper portion forming 4 deltate valves, seeds ± in several vertical stacks per chamber; sepals not persistent.


Seed asymmetrically obovoid, ± 1 mm long, brown.

A. C. Gibson & B. A. Prigge