IV. HESPERALBIZIA Barneby & Grimes
Hesperalbizia Barneby & Grimes, gen. nov. monotypicum, signis sequentibus inter affines praestans: stipulae parvae membranaceae basi cordatae; foliola pinnatim venulosa; cujusque capituli flores parvi homomorphi sessiles: ulterius a Pseudosamanea legumine longistipitato pleurumque 8-12 (nec 12- 30)-spermo seminumque areola clausa absimile. — Sp. unica: H. occidentalis (T. S. Brandegee) Barneby & Grimes - Albizzia occidentalis T. S. Brandegee. — Etymology: Gr. hesperos, the evening star, by extension, the West + the generic name Albizia.
Xerophilous but macrophyllidious, drought-deciduous trees, the inflorescence precocious, preceding or coeval with flush of new foliage, the terminal meristem continous beyond it. Stipules small, membranous (deciduous), cordate at base. Lf-formula iii— viii/5—10; 1ft-venation pinnate. Fls capitulate, sessile, homomorphic. Pods long-stipitate, broad-linear piano-compressed, 8-12(-13)-seeded, dehiscence inert, through both sutures; pleurogram of seed-faces complete. — Sp. 1, of SW Mexico.
Although the piano-compressed, stiffly papery pod of H. occidentalis is of a type conventional in Albizia sens. lat., the species is morphologically isolated by the syndrome of characters listed in the diagnosis. Especially noteworthy is the absence of a modified central flower, which we interpret, in the context of the albizioid Ingeae, as a derived state. In general aspect, H. occidentalis somewhat resembles the paleo-tropical Albizia lebbeck, but this differs in linear-oblong stipules, palmate-pinnate (not simply pinnate) venation of leaflets, and pediceled peripheral flowers.