Oenothera biennis L.

Habit

Biennial herb

Family Description

Perrenial or annual herbs( in Bhutan), some woody at base, rarely aquatic. Leaves opposite or spiral, simple, entire or toothed; stipules absent or reduced. Flowers actinomorphic or zygomorphic , 2- or 4-merous, rarely 5-7-merous, bisexual, solitary or in axiles of leaves, or in racemes, often subtended by reduced bracts. Flora tube short or absent. Sepals 2-5(-7), valvate.Petals 2-5(-7), free. Stamens as many as or twice as the sepals; anthers versatile or sometimes nearly basifixed. Ovary inferior, 1-5-celled; style simple; stigma lobed, clavate, or globose.Fruit a capsule, berry, or nut, loculicidal or indehiscent; seeds smooth or variosly papillose, with or without an apical tuft of hairs(coma).

Genus Description

Annual, biennial or perenial hebs, caulescent or sometimes stemless, with taproot or spreading underground parts; basal rosette usually present, but often ephemeral. leaves alternate, stipules absent. Flowers 4-merous, actinomorphic, in axils of upper leaves, opening about sunset or about sunrise. Floral tube well developed ansd prolonged beyond ovry, decidous soon after anthesis. Petals yellow, purple or white. Stamens 8. Stigma deeply 4-lobed.Fruit a loculicidal capsule, rarely indehiscent, sessile or sometimes pedicellate, mostly staight, terete or somewhat 4-angled. Seeds usually numerous, naked, in 1-2(-3) rows or in clusters in each of the locules.

Species description

Erect biennial herb, forming a basal rosette; stems 30-200cm, branching from base or above, or simple, with dense to scattered short appressed stiff hairs and longer spreading hairs, which are often-based and glandular-pubescent. Rosette leaves 10-30 x 2-5cm; apex acute to long acute, base attenuate, surfaces moderately appressed stiffly hairy, the upper ones sometimes also erect-pubescent or glandular-puberulent, denticulate, often with wavy margins, sessille or shortly petile; passing upward gradually into slebder bracts. Inflorescence a simple spike, usually with secondary spikes below main one, appressed stiffly hairy and glandular-puberulent, sometimes also with longer swollen-based hairs; flowers opening about sunset. Floral tube 20-40mm, Yellowish, with scattered hairs. Sepals 12-25mm; subulate free tips 1-3mm. Petals yellow, 12-30 x 14-30mm, retuse to emarginate. Style 30-55mm; stigma surrounde by anthers, lobes 3-6mm. Capsules 2-4cm, 4-6mm thick at base, narrowly ellipsoid to ellipsoid, pubescent. Seeds angled, 1.1-2 x 0.6-1.1mm, dark brown, the surface regularly pitted.