Trees or shrubs, to 10 m, trunk often multi-stemmed from base. Leaves deciduous, pinnae 8–20; stipules cadu­cous, pale yellowish green, subfoliaceous, dimidiate-cordate, 0.8–1.1 × 0.4–0.6 mm, base oblique, apex acuminate, surfaces puberulent; petiole yellowish brown to yellowish olive, 0.7–2.2 cm, pilose; petiolar nectary medial to distal of first pinnae, yellowish brown to reddish brown, conical, 0.5–1.2 × 1–1.5 mm; rachis yellowish brown to yellowish olive, 3–10 cm, pilose to glabrescent; rachilla opposite, yellowish brown to yellowish olive, 2.5–9 cm, pilose to glabrescent; pulvinules 0.2–0.4 mm; leaflets 20–38 per pinna, blade oblong, 3.8–8.5 × 1.5–2.9 mm, papery, base obliquely rounded to truncate, venation palmate-pinnate, midvein slightly eccentric, apex obtuse, surfaces subappressed-pilose to glabrescent, margins ciliate. Peduncles dark yellowish brown, 2.2–3.8 cm, spreading-pilose to densely pilose. Inflorescences 50–70-flowered, racemes, ovoid-cylindrical; bracts caducous, brown, spatulate, 1.2–5.5 × 0.2–4.5 mm. Pedicels 0.2–1 mm, canescent. Flowers: calyx pale white to yellowish white maculate, 2.3–3.2 × 1.2–1.7 mm, puberulent; lobes cucullate, 0.4–0.9 mm, apex acute to obtuse, canescent; corolla pale yellowish green maculate, campanulate-infundibular, 3.3–4.4 × 1.2–1.7 mm, canescent; lobes cucullate, 0.8–1.2 mm, apex acute to obtuse, canescent; stamens 24–36, white to pale yellowish white, 7.4–9.2 mm, mostly connate 2.2–3.7 mm; ovary subsessile. Legumes dark reddish brown to brownish black, slightly falcate, 8–20 × 1.5–3 cm, dehiscent, crustaceous, base attenuate, apex acuminate, surfaces glaucescent, glabrous; stipe 0.3–1.3 cm. Seeds dark brown to dark olive brown, oval, 6.4–10.2 × 5–8 mm; pleurogram oval, nearly complete. 2n = 26.

Phenology: Flowering Mar–May.
Habitat: Temperate upland shrub grasslands, crassicaulescent deserts.
Elevation: 600–1600 m.

Distribution

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Ariz., Mexico (Chihuahua, Sinaloa, Sonora).

Discussion

Natural distribution of Lysiloma watsonii is restricted to southern Arizona (Pima County) and northern Mexico; it is widely introduced in Maricopa, Pima, and Pinal counties in the greater Phoenix area.

The bark of Lysiloma watsonii is used locally as an astringent, purgative, and tea. Roasted seeds are made into atole. The hard wood is utilized in woodworking and in general construction. The species is also planted as a landscape ornamental in Arizona.

Selected References

None.

Lower Taxa

None.