Herbs, profusely branched from base. Stems prostrate or ascending, to 15(–32) cm, strigose or glabrous. Leaves: stipules linear-lanceolate or elliptic-ovate, to 5[–7] mm; pinnae (1 or) 2–7[–12] pairs; leaflets 10–40[–54], blades widely elliptic, elliptic-ovate, lanceolate, or linear-lanceolate, 3.5–14 × 1–6 mm, surfaces strigose or glabrous abaxially, glabrous adaxially. Peduncles solitary, axillary, 0–2.9(–4) cm. Heads (2–)5–12-flowered, compact, obconic. Flowers sessile or pedicellate, pedicels 0–2 mm; calyx (1–)2–3 mm, sparsely hairy apically; corolla 4–5[–7.5] mm, with few hairs near apex; filaments 19–28, white (drying pink), 9–13 mm. Legumes brown, linear-lanceolate or oblanceolate, to 5.8 × 0.6 cm, thickly papery, weakly translucent, glabrous or sparsely strigose. Seeds 1–6, obovoid, 5–6 × 3–4 mm.

Distribution

sw United States, n, c Mexico.

Discussion

Varieties 3 (2 in the flora).

Calliandra humilis ranges from central Mexico to Puebla and to southwestern United States; at the local level, it appears to be uncommon.

Variety gentryana Barneby is known from northern Mexico.

Calliandra humilis can be readily distinguished by being a perennial herb with relatively short stems, relatively small, obconic heads, and relatively short filaments. It shares with C. biflora the unusual condition of being herbaceous; however, the two species appear not to be phylogenetically related. These two species can be distinguished by the more numerous, shorter stems, leaves with usually more pairs of pinnae (var. humilis), obconic heads with more numerous flowers, and flowers with shorter filaments of C. humilis.

Selected References

None.

Lower Taxa

Calliandra humilis var. humilis, Calliandra humilis var. reticulata

Key

1	Pinnae (2 or)3–7[–12] pairs; leaflets 18–40[–54], blades 3.5–6 × 1–1.8 mm, venation perceptible with magnification.	Calliandra humilis var. humilis
1	Pinnae 1–3 pairs; leaflets 10–22, blades 6–14 × 2–6 mm, venation perceptible without magni­fication.	Calliandra humilis var. reticulata