Functionally herbaceous or subherbaceous, fire-resistent subshrubs of campo habitats, the one or few stems erect or incurved-ascending from oblique lignescent rootstock, commonly simple 1-4 dm and monocephalous, less often 2-5-branched distally and each efoliate or 1-lvd branch monocephalous, exceptionally attaining 7 dm, the units of inflorescence all terminal to their axis of origin, the stems, lvs, and fls glabrous to variably pilose, pilosulous, or silky-strig(ul)ose, the small imbricate lfts almost always facially glabrous, either cili(ol)ate or not, bicolored, lustrous dark olivaceous above, paler beneath, the proportionately large umbelliform capitula shortly emersed from foliage, white to pink or crimson. Stipules narrowly ovate, narrowly lance-elliptic, or linear- lanceolate 2-5.5(-7) x 0.5-2.2(-2.5) mm, weakly 3-5(-7)-nerved, tardily deciduous, expanded at base into a shallow cupule nidulating the pulvinus of each lf-stk. Lf-formula (ii—)iii—viii/20-42; lf-stk of longer lvs 3-7.5 cm, the petiole (4—)6— 13 cm, the rachis cupulately distended at insertion of pinnae, the longer interpinnal segments 5—13(—18) mm, the ventral groove bridged between pinnae; pinnae scarcely (but sometimes randomly) graduated, the rachis of longer ones 2.5-7.5(-8) cm, the longer interfoliolar segments 0.7-1.9 mm; lft-pulvinules 0.1-0.3 mm; lfts subequilong except at very ends of rachis, in outline narrowly lance-oblong from obtusangulate base, acute or mucronulate, those near mid-rachis (3.3-)3.5-7.5 x 0.75-1.9 mm, 3-5 times as long as wide; venation palmate-pinnate, the straight or distally subporrect midrib forwardly displaced to divide blade l:2-2.7(-3), giving rise on posterior side to 2-4(-5) widely diverging secondary veinlets brochidodrome well within the plane margin, the 1-2 posterior primary nerves very short, the whole venation pallid and finely prominulous dorsally, immersed or almost so above. Peduncles (measured from furthest lf) 2.5-10.5 cm, bracteolate or not; capitula cymose-umbelliform 12-26-fld, the clavate receptacle including short terminal pedestal 2-5 mm; floral bracts often 0, those subtending random outermost fls linear or linear-oblanceolate 2-4.5 mm, deciduous; fls of most capitula dimorphic, the peripheral ones long-pedicellate and the central one either short- pedicellate or subsessile, stouter than the rest but hardly longer and not otherwise modified, in some capitula wanting or degenerate; PERIPHERAL FLS: pedicel to 5-26 x 0.4—1.1 mm, sulcate lengthwise, dilated under the calyx proper into a solid turbinate head 0.8-1.7 mm tall; perianth (5-7-merous) thin-textured, whitish, brownish or pink-tinged, either glabrous or variably pubescent, weakly few-nerved; calyx narrowly or openly campanulate 3-5.2(-6) x 2.3-3.5(4) mm, the ovate or depressed-ovate teeth (0.4-)0.8-1.4 mm; corolla vase-shaped (8.2-)9-14 mm, the ascending ovate lobes often unequal, the longest ±2.5-4.5 mm; androecium 34-44-merous, 4.5-6(-7) cm, the stemonozone (1-)1.2-2.4 mm, the tube 2.5-5(-6) mm; no intrastaminal nectary; ovary subsessile, at anthesis smooth or micropapillate. Pods 1-4 per capitulum, erect, in profile 5-9 x 0.6-1.2 cm, the sutural ribs 2.5 mm wide or more, the recessed valves not perceptibly venulose, densely gray- and sordid-pilose overall.

Calliandra brevicaulis is instantly recognized by its truly terminal peduncles, and is further notable in its area of dispersal for short stems arising annually from an often strongly lignescent, sometimes creeping rootstock, and for the proportionately great size of the umbelliform capitula. The plants are diverse in length, orientation, and distribution of hairs on stem, leaves, and flowers, several states of which were described by Hassler as varieties or forms. Much of the variation seems random, even though relatively stabilized within a population. There is, however, a strong correspondence between dispersal, leaflet-number, and pubescence of the flowers which calls for recognition of two infraspecific taxa.