Shrubs or small trees of maritime habitats with pneumatophores, and terete branchlets conspicuously swollen at nodes. Leaves simple, opposite, lanceolate, oblong-lanceolate or elliptic, decussate, coriaceous, entire, exstipulate. Inflorescence terminal or axillary, often capitate cymes. Flowers regular, hermaphrodite, sessile, yellow or yellowish. Calyx deeply 5-lobed with imbricate, ovate lobes subtended by a false involucre of a scale-like bract and 2 alternate scale-like bracteoles (prophylls). Corolla gamopetalous, short, cylindrical, campanulate-rotate, actinomorphic or subequal, deeply 4-lobed. Stamens 4, inserted in throat of the corolla tube, equal or somewhat didynamous. Ovary superior with 2 united carpels and free central placentation; style shortly divided; ovules 4, pendulous. Fruit a capsule, broadly ellipsoid, compressed, dehiscent by 2(—4) thick valves; seed usually only one, erect; embryo with 2 large, longitudinally folded cotyledons and villous radicle, viviparous; endosperm fleshy.
An unigeneric family often included under Verbenaceae. It was first published by Endlicher (Enchiridon 314.1841) as Avicennieae. Moldenke (vide A. Gunderson, Families of Dicots. 202. 1950) following Endlicher and Eichler, pointing out some important anatomical and other characters, accepted Avicenniaceae as a separate family, and recently F.N. Hepper (Fl. West Trop. Africa, 2:448. 1963) recognized it so. Growth in diameter of trunks and branches brought about by concentric layers of mestone rings; branches prominently nodose and articulate; calyx subtended by a pseudo-involucre composed of a scale-like bract and 2 alternate scale-like bracteoles (prophylls); corolla rotate-campanulate; dehiscent capsule; free central, ± 4 winged placenta; 4 pendent, orthotropous ovules, viviparous embryo and fleshy endosperm are characters sufficient to justify separate identity of Avicenniaceae as a family distinct from Verbenaceae.
Acknowledgements: We are grateful to the United States Department of Agriculture for financing this research under P.L. 480. Thanks are also due to Mr. B.L. Burtt for his help and guidance.