Dense, more or less hemispherical, perennial herb or sub-shrub from a branched, woody caudex, 1-3 dm high; stems and leaves pubescent with appressed, 3-rayed to dendritic trichomes; leaves alternate, succulent, (18-)22-40(-48) mm long, (4-)6-12(-14) mm wide, oblanceolate to spatulate, margins entire or, rarely, obscurely sinuate-dentate; inflorescences compact, ebracteate racemes (1.5-)2-4.5(-6.5) cm long, equaling or slightly exceeding the leaves; pedicels ascending to divaricate, (3-)4-9(-13) mm long; flowers white, conspicuous, 1-1.5 cm wide; sepals 4, green, pubescent, (3-)4-6 mm long, 1-1.5 mm wide, broadly lanceolate; petals 4, white and rarely fading to pale lavender, glabrous, 7-9 mm long, 3.5-4.5 mm wide, obovate to broadly spatulate, attenuate at the base; stamens weakly tetradynamous, 2.5-5.5 mm long, about equaling the sepals; carpels 2, connate, ovary tomentose, 2-4 mm long, style glabrous, 1.3-2.2 mm long; fruit an obcompressed (angustiseptate), oblong silique, crispate (tortulose) and usually incurved, 5-12(-16) mm long, 2.2-3 mm wide, with 20-40 seeds. Flowering late July to early September.
The crispate fruits of N. hypercorax are unique in the genus and allow this species to be easily distinguished from other Nerisyrenia in the area. Nerisyrenia linearifolia is frequent on gypsum in Otero and Chaves counties and, if fruits are not present, is distinguished from N. hypercorax by having linear leaves.
New Mexico: Chaves County and Otero County, along the west base of the Guadalupe Mountains.
Nerisyrenia hypercorax is a gypsophile, found only on sparsely vegetated exposures of gypseous clay of the Yeso Formation, from Pup Canyon north to 1.5 miles north of the Chaves / Otero county line along the west base of the Guadalupe Mountains. South of Pup Canyon, similar gypsum exposures have N. linearifolia rather than N. hypercorax. Extensions of this band of gypsum further north have not yet been surveyed. Frequent associated species include Haploësthes greggii, Thelesperma megapotamicum, Tiquilia hispidissima, Chamaesyce fendleri, Mentzelia humilis var. guadalupensis, Acleisanthes lanceolata, Oenothera hartwegii subsp. filifolia, Sporobolus nealleyi, and Chamaesaracha pallida. Within this habitat, N. hypercorax is usually most abundant in and along the edges of deeply-incised ravines.
The area where N. hypercorax is found is remote and subject to very little disturbance other than cattle grazing. Gypsum in the area appears to be rarely visited by cattle, presumably due to the steep topography and low forage production associated with these outcrops. Applications of the herbicide tebuthiuron have been conducted adjacent to this band of gypsum to remove shrubs and, although the effects of this herbicide on N. hypercorax are not known, extension of these vegetation treatments onto gypsum would be a cause for concern.
Alexander, P.J., N.A. Douglas, H. Ochoterena, H. Flores-Olvera, and M.J. Moore. 2014. Recent findings on the gypsum flora of The Rim of the Guadalupe Mountains, New Mexico, U.S.A.: a new species of Nerisyrenia (Brassicaceae), a new state record, and an updated checklist. Journal of the Botanical Research Institute of Texas 8(2): 383-393.