Family Humiriaceae

Humiriaceae Juss.

Alternatively Houmiriaceae Juss.

Habit and leaf form. Trees, or shrubs. Leaves evergreen; alternate; spiral, or distichous; leathery; petiolate; non-sheathing; not gland-dotted; aromatic (often, with ‘balsamic’ juice), or without marked odour; simple. Lamina entire; pinnately veined; cross-venulate. Leaves stipulate, or exstipulate. Stipules when present, caducous (tiny). Lamina margins entire, or crenate, or serrate.

Leaf anatomy. Stomata present; anomocytic, or paracytic.

Lamina dorsiventral; without secretory cavities. The mesophyll with sclerencymatous idioblasts, or without sclerenchymatous idioblasts; containing calcium oxalate crystals. The mesophyll crystals druses, or solitary-prismatic.

Stem anatomy. Secretory cavities absent. Cork cambium present; initially superficial. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent. Xylem with tracheids. Vessel end-walls oblique; scalariform. Wood parenchyma apotracheal and paratracheal.

Reproductive type, pollination. Unisexual flowers absent. Plants hermaphrodite.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in panicles. The ultimate inflorescence unit cymose. Inflorescences terminal (rarely), or axillary; axillary or rarely terminal thyrses. Flowers regular to somewhat irregular. Free hypanthium absent. Hypogynous disk present; intrastaminal; of separate members, or annular (cupular).

Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5 (but the lobes of the two outer members sometimes suppressed); 1 whorled; gamosepalous (usually connate below into a thickened tube or cup); three or five blunt-lobed; cupuliform, or tubular; persistent; imbricate. Corolla 5; 1 whorled; polypetalous (the petals usually 3–5 nerved, thick); imbricate, or contorted; persistent, or deciduous.

Androecium 10–30, or 40–100 (Vantanea). Androecial members branched (fascicled, with trunk bundles, or with clusters and singles); free of the perianth; coherent (the filaments connate for much of their length into a tube); 1–4 whorled, or 5 whorled (one to several series). The androecial bundles when present, alternating with the corolla members. Androecium exclusively of fertile stamens, or including staminodes. Stamens 10–100 (to ‘many’); diplostemonous to polystemonous; sometimes in 5 antesepalous clusters of three, and 5 antepetalous singles. Anthers dorsifixed to basifixed, or adnate (to the base of the fleshy connective); versatile; dehiscing via longitudinal slits; bilocular (the locules often well separated), or four locular; bisporangiate, or tetrasporangiate; conspicuously appendaged. The anther appendages apical (the connective expanded and prolonged). Pollen shed as single grains. Pollen grains aperturate; 3(–4) aperturate; porate (rarely), or colporate.

Gynoecium (4–)5(–7) carpelled. Carpels reduced in number relative to the perianth to isomerous with the perianth to increased in number relative to the perianth. The pistil (4–)5(–7) celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior. Ovary (4–)5(–7) locular; sessile. Gynoecium stylate. Styles 1; apical. Stigmas 1; (4–)5(–7) lobed (or entire). Placentation axile to apical. Ovules 1–2 per locule; pendulous; epitropous (the micropyle directed upwards and outwards); with ventral raphe; when paired, superposed; anatropous; bitegmic; crassinucellate. Endothelium differentiated. Endosperm formation probably nuclear.

Fruit fleshy (with more or less fleshy exocarp); indehiscent; a drupe (the endocarp woody, sometimes with resin cavities, then buoyant for distribution by water); usually 1 seeded, or 2 seeded (germinating by valves or opercula). Seeds copiously endospermic. Endosperm oily. Cotyledons 2 (?). Embryo slightly curved, or straight.

Physiology, biochemistry. Ellagic acid present.

Geography, cytology. Paleotropical and Neotropical. Tropical. Tropical America, and one species in tropical West Africa. X = 12.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Rutiflorae; Geraniales. Cronquist’s Subclass Rosidae; Linales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; fabid; Order Malpighiales.

Species 50. Genera 8; Duckesia, Endopleura, Hylocarpa, Humiria (Houmiria), Humiriastrum, Sacoglottis, Schistostemon, Vantanea.

Cuatrecasas 1961.

Illustrations.
• Technical details: Humiria.