General: Shrub or small tree 1–3 m tall, with slender, sparsely puberulent, but becoming glabrate branchlets and weak, needle–like straight stipular spines 2–3 mm long, ascending and persistent. Leaves:: Leaves in 5–10 pairs of pinnae and 20–40 small pairs of leaflets, each 1.5–3 mm long, linear, acute to apiculate, 2–3 mm long; petioles u–shaped in cross section, puberulent but glabrate with age.Flowers:: Cream colored flowers in spikes 2.5–5 cm long; flowers sessile, calyx broadly cup–shaped, 0.5–1 mm deep, glabrous or margins ciliolate, petals 2 mm long, glabrous.Fruits:: Flat, veiny pods 7–15 cm long, 1–1.8 cm wide, slightly constricted between seeds or margins straight. Ecology:: Found in rocky canyons and on hillsides from 4,000–5,500 ft (1219–1676 m); flowers July–September.Notes:: Distinguished as a medium shrub with semi-weak, sometimes whitish, waving branches; small, straight,paired spines at some nodes but otherwise spineless; finely divided bright green leaves with many leaflets; elongated white flower clusters; and wide,flattened pods. Note the nomenclature change for the entire genus. Turner et al. 1995 suggest that A. millefolia may not come much further north than Pima county, a suggestion supported by even collections data. Ethnobotany:: Unknown, but other species in this genus have uses. Etymology:: Acacia is from Greek akakie taken from ake or akis, ‘a sharp point, millefolia means many leaved. Sources:
Wiggins 1964, Benson and Darrow 1981, Turner et al.1995, Kearney and Peebles 1969