XI. HAVARDIA SMALL
Havardia Small, Bull. New York Bot. Gard. 2: 91. 1901. sens. str. — Generitypus: H. brevifolia (Bentham) Small = Pithecellobium brevifolium Bentham = H. pallens (Bentham) Britton & Rose.
Pithecolobium sect. Ortholobium Bentham, Trans. Linn. Soc. London 30: 592, ex parte (spp. 82, 83). 1875. — Sectionis lectotypus: P. albicans (Kunth) Bentham = Havardia albicans (Kunth) Britton & Rose.
Havardia sensu Britton & Rose, N. Amer. Fl. 23: 40, ex parte (spp. 1-5). 1928; Nielsen, 1981: 184, ex parte, exclus. syn. plur.
Trees (2-)3-11 m. Stipules associated with primary lvs subulate or conical, spinescent. Lf-formula i- ix(—xiii)/7—36, the lfts either opposite or (H. albicans) alternate along pinna-rachis, the largest ±2.5-10(12) mm; lf-nectaries sessile, the first situated below proximal pinna-pair; venation of lfts pinnate or simple, exceptionally obscurely palmate-pinnate. Inflorescence various, the capitula or (H. mexicana) capituliform racemes arising either from lf-axils of long-shoots, coevally with or preceding the lf, or from brachyblasts, or from both; calyx either shallowly or deeply campanulate 1-3.4 mm; corolla 3-5.5(-6.5) mm, the lobes at full anthesis either erect or recurved; androecium (28-)30-52-merous, 9-14.5 mm, the basal callosities within the tube often obscure or 0, rarely forming a pronounced nectarial disc; ovary subsessile or (H. pallens) shortly stipitate. Pods broad- linear straight, piano-compressed, 8-13-seeded, the chartaceous or thinly coriaceous, stiffly papery valves low-convex over each seed on one face or (H. campylacanthus) on both, the cavity continuous; dehiscence tardy, inert, through both sutures; seeds transverse on dilated, distally sigmoid funicle. —Spp. 5, of warm-temperate, and seasonally dry tropical, Mexico, adjacent Texas, and Central America.
Except for spinescent stipules and lack of a dimorphic flower in the capitula, the species of Havardia resemble Albizia sect. Arthrosamanea, their young inflorescence recalling the panicle of pseudoracemes prevalent in Albizia. The inflorescence of the section shows forms transitional between the panicle of pseudoracemes prevalent in Albizia and that of the xerophytically modified genera Sphinga, Painteria, and Ebenopsis: at one extreme H. albicans and H. pallens, where most capitula are borne on new growth, axillary to hysteranthous leaves, at the other H. campylacanthus, which forms a passage to Sphinga. In all but H. campylacanthus, in which the valves of the ripe pod are biconvex over each seed, the pods of Havardia are undulately corrugate lengthwise, as in the genus (Mimoseae) Parapiptadenia Brenan. Specialized features of individual species of Havardia are the pronounced ovary-stipe of H. pallens, the alternate leaflets of H. albicans, and the pedicellate flowers of H. mexicana.