Herbs annual, biennial, or short-lived perennial; from taproot. Stems erect. Inflorescences dense or lax, erect, terminal. Flowers: buds erect, terete to weakly quadrangular, with free tips terminal, erect or spreading; floral tube slightly curved upward or straight, 15–47 mm; petals rhombic to elliptic or rhombic-ovate. Capsules curved upward or straight, narrowly lanceoloid to lanceoloid, subterete, 2–4 mm diam. Seeds numerous, in 2 rows per locule, brown to dark brown, often flecked with darker spots, ellipsoid to broadly ellipsoid, surface reticulate and regularly pitted. 2n = 14.

Distribution

c, e North America.

Discussion

Species 5 (5 in the flora).

Subsection Candela consists of five closely related species found at low elevations in the cen­tral and eastern United States (W. Dietrich and W. L. Wagner 1988). They are self-incompatible (Oenothera cordata, O. rhombipetala, and some populations of O. heterophylla) or self-compatible (O. clelandii, O. curtissii, and some populations of O. heterophylla). The flowers are vespertine, outcrossing and pollinated by hawkmoths, or autogamous in two PTH species (O. clelandii and O. curtissii) (Dietrich and Wagner). They were treated as part of a rather heterogeneous subg. Raimannia by P. A. Munz (1965). W. Stubbe and P. H. Raven (1979) placed these species in a reconfigured, narrower subsect. Raimannia based on crossing results; Dietrich and Wagner segregated them as a new series within subsect. Raimannia based on the earlier crossing results and morphology. The group is characterized by the usually dense flowering spikes with several flowers opening each evening, straight floral tubes, and petals acute to rounded at apex. R. A. Levin et al. (2004) did not test this group’s monophyly, since they included only O. heterophylla, but the overall morphological similarity of these species and the clear synapomorphy of the petal shape support the monophyly of the subsection. Wagner et al. (2007) elevated the group to the status of a subsection, because it does not group with subsect. Raimannia in the molecular analyses; instead, it forms a weakly supported clade with subsect. Oenothera, with which it shares a similar habit, dense spikes, and lanceoloid capsules. Cytological analyses (Dietrich and Wagner), showed that species of subsect. Candela are all diploid (2n = 14) with O. cordata, O. heterophylla, and O. rhombipetala bivalent-forming species, and O. clelandii and O. curtissii PTH species forming a ring of 14 chromosomes in meiosis.

Selected References

None.

Lower Taxa

Oenothera clelandii, Oenothera cordata, Oenothera curtissii, Oenothera heterophylla, Oenothera rhombipetala

Key

1	Petals 5–17 mm; stigmas surrounded by anthers at anthesis; pollen ca. 50% fertile.	> 2
1	Petals 15–35 mm; stigmas exserted beyond anthers at anthesis; pollen 85–100% fertile.	> 3
2	Inflorescences dense, 2+ flowers per spike opening per day.	Oenothera clelandii
2	Inflorescences lax, 1 or 2 flowers per spike opening per day.	Oenothera curtissii
3	Mature flower buds not overtopping spike apex; distal parts of plant strigillose, sometimes also sparsely glandular puberulent.	Oenothera rhombipetala
3	Mature flower buds usually overtopping spike apex; distal parts of plant glandular puberulent, villous, strigillose, or hirsute with pustulate-based hairs, especially sepals and floral tube, or glabrous.	> 4
4	Inflorescences dense; bracts longer than capsules they subtend, 1–3 cm.	Oenothera heterophylla
4	Inflorescences lax; bracts shorter than capsules they subtend, 0.5–1.7 cm.	Oenothera cordata