C. decrescens Killip & Macbride, Publ. Field Mus. Nat. Hist., Bot. Ser. 13 (Fl. Peru) 3: 71. 1943. — "[PERU.] Loreto: Mishuyacu, Klug 152." — Holotypus, US!; isotypus, NY!.

C. guildingii sensu Grisebach, 1864: 225 (but not introduced in Trinidad); R. O. Williams, Fl. Trin. Tob. 1(4): 298. 1931.

Macrophyllidious trees (2-)3-12(once reported 20) m tall with gray trunk and plagiotropic long-shoots, often appearing and sometimes truly glabrous, but the lf-axes and either the margin or the principal veins of lfts pilosulous or micropuberulent with sordid hairs 0.1-0.4(-0.5) mm, the lvs moderately bicolored, lustrous and reticulate on both faces, the capitula borne singly or less often geminate at stipulate nodes of very short, efoliate or 1-foliate brachyblasts axillary to coeval primary lvs, scattered along the leafy growth of current year; phyllotaxy distichous. Stipules broadly or narrowly triangular, rarely lanceolate, ±1—8(—11) x 0.6-1.3(-2) mm, finely 3-8-nerved dorsally when young, becoming smooth, deciduous. Lf-formula i/2— 5(-6), the lfts conspicuously accrescent, the small first pair seldom exactly opposite; lf-stks (2—)4—17(—19) x 0.7-1.5 mm, openly shallowly grooved ventrally, bicupulate at apex; rachis of longer pinnae (1.6-)2-6.5(-7) cm, the furthest interfoliolar segment (7-)9-18 mm; lft-pulvinules 0.4-1.9 x 0.5-1.4 mm, wrinkled; proximal pair of lfts (often of unequal size) asymmetrically rhombic-ovate, obscurely if at all acuminate, 5-22(-32) x 3-12(-20) mm, the distal pair inequilaterally or subdimidiately ovate-elliptic-acuminate from semicordate (broad-cuneate) base, at very apex either acutely triangular or obtuse apiculate, the largest (2-)2.5-8.2 x (0.8-)l-4 cm, ±2-2.8 times as long as wide; venation palmate-pinnate, the midrib either gently incurved or straight diagonal, the inner posterior primary nerve incurved-ascending well beyond midblade, the outer posterior ones much shorter, all these and the tertiary and reticular venules sharply prominulous on both faces. Peduncles 7-25(—34) mm, usually but not always bracteate near middle, thickened and arrect in fruit; capitula 10-24(-28)-fld, the receptacle 1.5-3 mm diam; bracts subulate 0.7-1.2 mm, persistent; fls commonly heteromorphic, one or more (sub)terminal ones scarcely different as to perianth but with dilated and exserted, whitish staminal tube, these fls pistillate and nectariferous but sometimes ill- developed (or perhaps absent), the rest staminate, with slender, either included or rarely exserted staminal tube; perianth of all fls thin-textured, glabrous or remotely either strigulose or pilosulous, either 4- or 5- merous, the calyx striate but the corolla not; PERIPHERAL FLS: pedicel often cryptic 0.15-0.5 x 0.4-0.8 mm; calyx campanulate 1.3-3 x 1-2.5 mm, the depressed or vestigial teeth 0.1-0.4 mm (one or more sinuses often more deeply split in late anthesis); corolla 5.8-9(-10) mm, the ovate (often unequal) lobes 1.2-2.4 mm; androecium 10-22(-24)-merous, attaining 42 mm, the tube 4.5-12 mm, the whole deep crimson or sometimes the tube pallid and only the tassel red; ovary at anthesis glabrous. Pods acroscopic, in broad profile 6.5-10.5 x 0.75-1.1 cm, thinly puberulent overall or glabrescent, the thickened sutural ribs 4-4.5 mm wide in dorsal view, sulcate lengthwise, the lignescent valves prominently, either obliquely or subvertically venulose; seeds (few seen) ±5-6 per pod, in broad view 9.5-10 x 5-6 mm, the papery testa pale brown or castaneous, often crumpled, pleurogram 0.

In moist lowland forest (Trinidad; state of Miranda, Venezuela; Amazonia) and ascending (n.-w. Venezuela; n. Colombia) into submontane forest and cloud-forest to 900-1850 m, discontinuously dispersed from n. Trinidad w. through the Venezuelan coastal cordillera to state of Yaracuy, thence s. and s.-w. to the Casiquiare in Venezuelan Amazonas, the eastern Andes in state of Táchira, and the lower Cauca valley in Antioquia, Colombia, s.-e. Ecuador (Napo), and n.-e. Peru (Amazonas, Loreto). — Map 29. — Fl. intermittently throughout the year. — Niaure (Trinidad); kunchai (Peru). — Described from St. Vincent Island, where probably cultivated in the botanical garden by Rev. Lansdown Guilding, and cultivated on Martinique in 1814 (BM!), but not since seen in the Lesser Antilles and not mentioned by R. A. Howard in volume 4 of Flora of Lesser Antilles (1988).

Calliandra guildingii resembles C. falcata, which has larger, more persistent stipules, only incipiently acuminate leaflets, and flowering brachyblasts arranged in leafless or only randomly leafy pseudoracemes. Whereas C. guildingii is found in moist lowland and upland cloud-forest, C. falcata is adapted to xeromorphic, semideciduous communities. A parallel instance of related but ecologically differentiated species is known in Senna robiniifolia and S. viciifolia, as described by Irwin and Barneby (1982: 520, sequ.). The species further is suggestive of an extreme form of C. surinamensis in which the leaflets are reduced in number to three or five, exceptionally six pairs per pinna and reciprocally dilated. Its lignescent, vertically venulose pod recalls that of C. magdalenae, but the papery seed-testa lacking pleurogram is that of the C. surinamensis complex.