Drought-deciduous microphyll shrubs of unknown stature, pilosulous with fine white hairs to ±0.4-0.5 mm, the young stems and lf-axes densely, the lfts and fls thinly so, eglandular, the umbels of heteromorphic fls solitary, pedunculate in the efoliate axils of short brachyblasts; phyllotaxy distichous. Stipules of primary lvs lanceolate ±4-6 x 1-1.5 mm, firm, weakly 3-6-nerved, persistent, those of brachyblasts similar but somewhat shorter. Lf-formula iii—iv/20—23; lf-stks 4-11 mm, the longer interpinnal segments 1-2.5 mm; pinnae subequilong, the rachis of longer ones 10-18 mm, the longer interfoliolar segments 0.3-0.5 mm; lfts subsessile, imbricate, the blades oblong from shallowly semicordate base, obtuse, the longer ones 1.8-2.7 x 0.7-1 mm, 2.7-2.8 times as long as wide; venation immersed. Peduncles 7-14 mm, bracteate above middle; umbels 12-20-fld, the subglobose receptacle 1.5-2 mm diam; bracts linear-lanceolate ±4 mm, caducous; pedicels graduated, those of outermost bisexual fls to 7-9 x 0.3-0.4 mm, those of 3-4 subterminal staminate ones ±1.5-2 x 0.9 mm; perianth of all fls 5-merous, thinly minutely puberulent eglandular; PERIPHERAL FLS: calyx ±5.5 mm, the campanulate tube ±1 mm, bluntly 5-angulate, the linear teeth ±4 x 0.2-0.4 mm; corolla 6.5 mm, the ovate lobes 2.8 mm; androecium 10-12-merous, ±4.5 cm, the stemonozone thickened internally ±1.4 mm, the tube 3.5 mm, disc 0; ovary glabrous, grooved laterally; SUBTERMINAL FLS: calyx ±7 mm, the tube 1.8 mm, the linear teeth 5.2 mm; androecium 20-mer- ous, the tube 3.5 mm, the tassel of unknown color (probably white brunnescent); ovary 0. Pod unknown.

In unrecorded habitat, but to be expected in caatinga, known only from slopes of Sa. do Pedro Segundo in n.-w. Piauí, Brazil. — Map 20. — Fl. probably after rains.

Calliandra imperialis resembles C. umbellifera and C. ulei in general habit and particularly in long- pedicellate peripheral flowers of the capitulum, but differs from both in linear calyx-teeth about four times as long as the tube. Its flowers lack the gland- tipped trichomes peculiar to C. umbellifera, and its androecium has only about half as many filaments (10-12, not ±22) as that of C. ulei.