Herbs to 8 dm. Leaves (1–)2–8(–9) cm; stipules subulate, 1–2 × 0.5 mm; blade linear-lanceolate. Inflorescence bracts linear-lanceolate, 1–2 × 0.5 mm. Pedicels 1–2 mm. Flowers: calyx tube 1.5–2.5 mm, glabrate, lobes 1.5–2.5 mm, proximalmost longer than lateral ones, adaxial 2 slightly more connate than lateral ones; corolla 5–6 mm, glabrous; filaments subequal; anthers relatively small, dehiscing longitudinally; pistil glabrous. Legumes light brown, terete, 20–30 × 2–3 mm, base blunt, apex acute, often terminating in persistent style base. 2n = 16.

Phenology: Flowering Aug–Nov.
Habitat: Disturbed areas.
Elevation: 50–1700 m.

Distribution

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Ariz., w, s Mexico.

Discussion

In the flora area, Sphinctospermum constrictum is known from Cochise, Pima, Pinal, and Santa Cruz counties.

The inflorescence of a solitary flower of Sphinctospermum constrictum includes a very short rachis and floral bract subtending the pedicel. Some­times, a short axillary shoot bearing a flower is borne from this same axil. This results in two flowers from a leaf axil along the main stem. The unifoliolate leaves and solitary flowers are superficially similar to those of 131. Genistidium, and molecular phylogenetic analysis suggests that these two are sister genera (R. Duno de Stefano et al. 2010).

Selected References

None.

Lower Taxa

None.