Habit and leaf form. Tall trees. Leaves alternate; leathery; simple. Lamina entire. Leaves exstipulate. Lamina margins entire.
Leaf anatomy. Stomata present; paracytic.
Lamina dorsiventral; without secretory cavities.
Stem anatomy. Secretory cavities absent. Internal phloem perhaps present (?cf. Convolvulaceae). Secondary thickening developing from a conventional cambial ring, or anomalous (?). ‘Included’ phloem absent.
Reproductive type, pollination. Fertile flowers hermaphrodite. Plants hermaphrodite.
Inflorescence, floral, fruit and seed morphology. Flowers solitary; axillary; (bi-) bracteolate; very irregular; zygomorphic; neither papilionaceous nor pseudo-papilionaceous; 5 merous. Floral receptacle developing a gynophore (this short and thick). Free hypanthium absent. Hypogynous disk absent.
Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; polysepalous; persistent; much imbricate. Corolla 5; 1 whorled; gamopetalous; contorted (and unilaterally induplicate); campanulate (with short lobes, these and the tube densely adpressed-ferrugineous-pubescent externally); unequal but not bilabiate.
Androecium 5. Androecial members adnate; free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 5; inserted near the base of the corolla tube; isomerous with the perianth; oppositisepalous; alternating with the corolla members; inflexed in bud (declinate at anthesis); filantherous (the anthers long exserted). Anthers basifixed; non-versatile; dehiscing via longitudinal slits; introrse.
Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil 2 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary 2 locular; stipitate. Gynoecium stylate. Styles 1 (deflexed in bud); apical. Stigmas 1; small, truncate. Placentation axile. Ovules 30–50 per locule (‘many’); anatropous.
Fruit non-fleshy; indehiscent (crustaceous); 4 seeded.
Geography, cytology. Paleotropical. Tropical. Madagascar.
Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Solaniflorae; Solanales. Cronquist’s Subclass Asteridae; Solanales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order Solanales (as a synonym of Convolvulaceae).
Species 1. Genera 1; only genus, Humbertia.