Oenothera biennis is a biennial, winter annual, or briefly perennial herb, from a thick, fleshy taproot; no mycorrhizal associations reported (Hall et al. 1988); flowering stem 0.5-2 m tall, leafy, often reddish, hollow, larger plants branched above.
Leaves alternate, 1st year rosette leaves long, narrowly egg-shaped, pointed at both ends, tinged with red spots, midrib white (Uva et al. 1997); 2nd year flowering stem leaves alternate, often almost stalkless, 8-20 cm long, 2-3 cm wide, becoming smaller upwards, lance-shaped (Hall et al. 1988), red when senescent, margin wavy and toothed.
Flowers yellow, petals 4, rounded, 1-2.5 cm long, sepals 4, green, 2 cm long, 0.4-0.5 cm wide; stamens 8; stigma with 4 spreading lobes; calyx tube 3-6 cm long; inflorescence leafy, stiffly erect, of spike-like racemes to 40 cm long at top of stem (Hall et al. 1988); flower buds with appendages at tips of enclosing sepals projecting above bud 0.1-0.5 cm, touching along their edges to form a tube; anthers shed pollen for when flowers still in bud and O. biennis is usually self-pollinating but open flowers may also be visited by bees and hawkmoths; flowers open in the evening; stigma lobes open early the following day (Gross and Kromer 1986; Lovell 1918); blooms July- Nov.
Fruit a green capsule, becoming dry, 2.5-4 cm long, 0.6 cm wide, stout, more-or-less cylindrical, narrow; fruit developing Aug.-Nov.(Hough 1983), capsule splitting into 4 lobes to release many small, irregularly angular seeds 0.8 cm long, dry plant persistent through winter; seeds eaten by goldfinches an sparrows (Martin et al. 1951). Parent plant dies after seed dispersal; winter plant recognized by spikes of long, 4-lobed capsules with tips curved outward (reflexed); seeds can remain viable for as long as 80 years; germination occurs in summer or fall producing a leafy rosette from a root crown (Levine 1995; Hall et al. 1988).
Wetland status: FACU-.
Frequency in NYC: Common.
Habitat: Open soil of disturbed areas, vacant lots, fill, roadsides, soil pH 5-7 (USDA, NRCS 2006).
Notes: Roots and shoots edible in moderation. Plant also has been used as a medicinal (Hall et al. 1988). Oenothera biennis plants are attacked by a number of insects including some that are host specific such as the aphids Aphis oenotherae and Macrosiphum gaurae; two weevils, Acanthoscelidius acephalus (D. P. Wijesinghe, personal communication), and Tyloderma foveolata (both Coleoptera: Curculionidae); larvae of moths in the genus Mompha (Lepidoptera: Momphidae), including M. stellella and M. brevivitella feed on O. biennis flowers and fruit; larvae of the moths Schinia florida (Noctuidae) and Conchylis oenotherana (Cochylidae) also feed on O. biennis. Fungi that grow on O. biennis include a number of powdery mildews such as Erysiphe cichoracaerum, E. polygoni, and Gnomonia misella; the rust Puccinia dioicae; and the leaf spot Septoria oenotherae. Many studies have been done on the genetics of O. biennis which is described as a “permanent translocation heterozygote,” breeding true due to a “balanced lethal system” and self-pollination (Cleland 1926; Levy and Levin 1974; Hall et al. 1988). Oenothera biennis cells have two totally different genomes of seven chromosomes each, instead of two copies of the same genome. During meiosis there is no pairing of homologous chromosomes. Instead, a ring of all 14 chromosomes forms during prophase, and each of the chromosome complexes migrates to a different pole. Although O. biennis is self-pollinated, viable gametes are only formed that include both chromosome complexes (i.e. heterozygous) because each complex in a homozygous state is lethal and produces no viable seed (Levin et al. 1972).