Gaura Linnaeus sect. Xenogaura P. H. Raven & D. P. Gregory, Mem. Torrey Bot. Club 23(1): 50. 1973

Herbs perennial, colonial; from woody taproot, spreading by rhizomes. Stems ascending to decumbent, several-branched from base, usually also irregularly branched distally, sometimes with a single, unbranched stem. Inflorescences slightly nodding. Flowers 4-merous, slightly to strongly zygomorphic, opening near sunset; floral tube 4–14 mm; petals white, slightly unequal; filaments with basal scales. Capsules erect, pyramidal in distal 1/2, conspicuously bulging at base of pyramidal part, strongly 4-angled, abruptly constricted to terete proximal part; sessile. 2n = 28.

Species 1: s, w United States, n, c Mexico.

Subsection Xenogaura consists of the allotetraploid (2n = 28) Oenothera hispida (= Gaura drummondii) from Texas to central Mexico. P. H. Raven and D. P. Gregory (1972[1972]) suggested that O. hispida arose following interspecific hybridization between O. suffrutescens (subsect. Campogaura) and a species in subsect. Stipogaura, possibly near O. mckelveyae. G. D. Hoggard et al. (2004) found that the pistillate parent of O. hispida was indeed O. mckelveyae or a close relative, but that the staminate parent probably came from a lineage related to O. dodgeniana or O. lindheimeri in subsect. Gaura. Oenothera hispida is not easily distinguished morphologically from O. suffrutescens (subsect. Campogaura), with which it shares similar fruit characters; O. hispida is an aggressively rhizomatous perennial with fruits conspicuously bulging on the distal half (Raven and Gregory). The rhizomatous habit makes this species potentially invasive, despite its self-incompatibility, but so far it has established itself most heavily in coastal southern California (W. L. Wagner et al. 2007).