Herbs annual, caulescent; from a taproot. Stems erect, unbranched or branched. Leaves in a basal rosette and cauline, cauline 1–2(–)4 cm; blade margins subentire or remotely dentate. Inflorescences solitary flowers in axils of distal leaves. Flowers opening near sunrise, nearly unscented; buds erect, terete, without free tips; floral tube 1–2 mm; sepals separating in pairs; petals bright yellow, fading pink, obcordate to obovate; stigma shallowly divided into 4 linear lobes. Capsules hard and leathery, ellipsoid-rhombic to subglobose, 4-angled, apex rounded or obtuse, proximal part tapering to a sterile, pedicel-like base (stipe), valve midrib raised at distal end, indehiscent or tardily dehiscent distally; sessile. Seeds usually numerous, clustered in each locule, ovoid, surface minutely papillose. 2n = 14.

Distribution

se, sc United States.

Discussion

Species 1.

Section Peniophyllum consists of a single diploid species. It has been treated as the sole member of subg. Kneiffia sect. Peniophyllum (P. A. Munz 1937, 1965) or sect. Kneiffia subsect. Peniophyllum (G. B. Straley 1977). It was separated from sect. Kneiffia by W. L. Wagner et al. (2007) because molecular data (R. A. Levin et al. 2004) failed to place these two groups in a single clade. Instead, Oenothera linifolia forms a very weakly supported clade with O. havardii (sect. Paradoxus), with which it shares no known morphological similarity other than characteristics of subclade B. The most distinctive characteristics of sect. Peniophyllum are the heteromorphic rosette versus cauline leaves, the cauline leaves crowded and linear, capsules ellipsoid-rhombic to subglobose, indehiscent or tardily dehiscent only at distal end, and the entire capsule falling from the plant prior to senescence. In most sections of Oenothera, the capsules are persistent on the stem, but in sect. Peniophyllum and two other sections (Gaura and Megapterium) of subclade B, the capsules often disarticulate from the plant. The flowers are self-compatible, diurnal, and autogamous or cleistogamous.

Selected References

None.

Lower Taxa

Oenothera linifolia