Oenothera sect. Emersonia Munz in N. L. Britton et al., N. Amer. Fl., ser. 2, 5: 105. 1965

Herbs perennial; from stout taproot, sometimes producing new shoots from lateral roots. Stems weakly erect to ascending [or decumbent], often rooting at nodes. Inflorescences solitary flowers in axils of distal leaves, sometimes forming a spike (O. organensis). Flowers: buds erect, weakly quadrangular, with free tips terminal, erect; floral tube straight, [55–]100–165(–190) mm; petals obovate to obcordate. Capsules straight, cylindrical to narrowly lanceoloid, subterete, [3–]4–5.5[–7] mm diam. Seeds in 2 rows per locule [or in 1 irregular row derived from 2 rows of ovules (O. maysillesii Munz)], dark reddish brown [brown], obovoid [oblong-ellipsoid], surface thickened at distal end and sometimes above raphe, [thickened area (O. maysillesii, O. stubbei W. Dietrich, P. H. Raven & W. L. Wagner) with an empty cavity]. 2n = 14.

Species 4 (1 in the flora): New Mexico, n Mexico.

As delimited by W. Stubbe and P. H. Raven (1979) and W. Dietrich et al. (1985), subsect. Emersonia consists of four species of mesic or xeric habitats (Oenothera stubbei) in pine-oak forests, meadows, and canyons, or boggy sites in grasslands, from scattered areas ranging from the Organ Mountains in southern New Mexico to southeastern Chihuahua, southern Coahuila and Nuevo León, northern Zacatecas and San Luis Potosí, and southern Durango, Mexico, 1100 to 2600 m. Two species are self-incompatible and two are self-compatible.

SELECTED REFERENCE Dietrich, W., P. H. Raven, and W. L. Wagner. 1985. Revision of Oenothera sect. Oenothera subsect. Emersonia (Onagraceae). Syst. Bot. 10: 29–48.