(Benth.) Seigler & Ebinger
Acacia constricta Benth.
In Arizona, it is found throughout the southern half of the state, extending southward throughout Sonora. Small disjunct populations have been collected from Baja California and Baja California Sur, the latter from the Magdalena Plain.
In the Sonoran Desert, Vachellia constricta is usually found in arroyos and washes, where it blooms in late spring (April–May), with a second round of blooms in July–October. The bloom depends on having a minimum amount of rain, followed by a period of warmth. The flowers offer no nectar and little pollen, and so tend to have few visitors.
Vachellia constricta typically grows to 2 metres (6.6 ft) in height, occasionally reaching 3 metres (9.8 ft). Its stems range from a light gray to a mahogany color, with pairs of straight white spines anywhere from 0.5 to 2 cm long.
The small leaves are even-pinnate, typically 2.5–4 cm in length, with each of the 3-9 pairs of pinnae made of 4-16 pairs of leaflets, which are about 3.5 mm long and 1 mm wide. The flowers occur in small yellow balls about 1 cm in diameter. The pods are relatively long and thin, up to 12 cm long but only 3–6 mm wide.
The leaves may drop in response to either dryness or cold.
- Seigler DS, Ebinger JE. (2005). "New combinations in the genus Vachellia (Fabaceae: Mimosoideae) from the New World.". Phytologia 87 (3): 139–78.
- Raymond M. Turner, Janice E. Bowers, and Tony L. Burgess, Sonoran Desert Plants: an Ecological Atlas (Tucson: The University of Arizona Press, 1995) pp. 15–16
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