Family Trigoniaceae

Trigoniaceae Endl.

Habit and leaf form. Trees, or shrubs, or lianas. Self supporting, or climbing. Leaves opposite (usually), or alternate (Trigoniastrum); simple. Lamina entire; pinnately veined. Leaves stipulate. Stipules interpetiolar; (those of opposite leaves) often concrescent; caducous.

Leaf anatomy. Mucilaginous epidermis often present. Stomata present; mainly confined to one surface (abaxial); paracytic.

Adaxial hypodermis sometimes present. Lamina dorsiventral. The mesophyll containing mucilage cells (in the hypodermis), or not containing mucilage cells.

Stem anatomy. Cork cambium present; initially superficial. Medullary bundles present (?), or absent. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. Xylem with tracheids. Vessel end-walls simple, or scalariform and simple. Wood parenchyma apotracheal, or apotracheal and paratracheal.

Reproductive type, pollination. Plants hermaphrodite. Pollination entomophilous.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in cymes, or in racemes, or in panicles (or thyses). The ultimate inflorescence unit cymose. Inflorescences terminal, or axillary; various, partly or wholly cymose. Flowers bi- or tri- bracteolate; very irregular; obliquely zygomorphic. The floral irregularity involving the perianth and involving the androecium. Flowers ‘pseudo-papilionaceous’ (the posterior ‘standard’ interior); cyclic. Free hypanthium present (slight), or absent. Hypogynous disk present; of separate members (in the form of (1)2–3 glands, usually adjoining the slit in the staminal tube).

Perianth with distinct calyx and corolla; 8, or 10; 2 whorled; isomerous, or anisomerous. Calyx 5; 1 whorled; gamosepalous; unequal but not bilabiate; neither appendaged nor spurred; imbricate; with the median member posterior. Corolla 3, or 5; 1 whorled; polypetalous; imbricate, or contorted, or valvate (rarely, or subimbricate); unequal but not bilabiate (the petals usually 5, the two anterior (lower, outer) members forming an often saccate keel, the posterior (inner, upper) one forming a basally usually saccate or spurred standard, the two laterals forming flat, spathulate wings); spurred (sometimes, via the standard), or not spurred.

Androecium 5–12. Androecial members free of the perianth; markedly unequal; coherent (unilateral on the anterior side of the flower, joined by their filaments); 1 adelphous (the long or short staminal tube split posticously); 1 whorled. Androecium including staminodes (usually), or exclusively of fertile stamens (sometimes). Staminodes when present, i.e. usually (1–)3–6. Stamens 5–8; isomerous with the perianth to diplostemonous. Anthers dehiscing via longitudinal slits. Pollen grains aperturate; 3–5 aperturate; porate.

Gynoecium 3(–4) carpelled. Carpels reduced in number relative to the perianth. The pistil 1–3(–4) celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary 1–3(–4) locular. Gynoecium stylate. Styles 1; apical. Stigmas 1 (simple); truncate, or capitate. Placentation when unilocular, parietal (with deeply intruded placentas); axile. Ovules in the single cavity when unilocular, 2–6 (?); when plurilocular, 1–20 per locule (to ‘rather numerous’); pendulous to ascending; epitropous; often biseriate; anatropous; bitegmic; crassinucellate (but becoming ‘tenuinucellate’ at maturity by absorption of the nucellus). Outer integument contributing to the micropyle. Endosperm formation ab initio nuclear.

Fruit fleshy, or non-fleshy (?); dehiscent, or indehiscent; a capsule (usually), or a samara (three winged, in Humbertiodendron and Trigoniastrum). Capsules when capsular, septicidal. Dispersal of seeds by wind or water. Seeds non-endospermic; conspicuously hairy (usually, long-pilose), or not conspicuously hairy. Embryo well differentiated. Cotyledons 2 (thin, flat). Embryo straight (usually or always transverse?). Testa densely hairy. Micropyle zigzag.

Seedling. Germination phanerocotylar.

Physiology, biochemistry. Aluminium accumulation not found.

Geography, cytology. Paleotropical and Neotropical. Tropical. Madagascar, Southeast Asia, Central and tropical South America. N = about 10.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Rutiflorae; Polygalales, or Geraniales (?). Cronquist’s Subclass Rosidae; Polygalales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; fabid; Order Malpighiales.

Species 35. Genera 4; Humbertiodendron, Trigonia, Trigoniastrum, Trigoniodendron.

Illustrations.
• Technical details: Trigonia (Lindley).