| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### 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; concrescent (often, when the leaves are opposite), or free of one another; caducous.

Leaf anatomy. The leaf lamina dorsiventral. Mucilaginous epidermis often present. Stomata present; mainly confined to one surface (abaxial); paracytic. Hairs present; eglandular; exclusively unicellular. Unicellular hairs simple. Complex hairs absent. Adaxial hypodermis sometimes present. The mesophyll containing mucilage cells (in the hypodermis), or not containing mucilage cells; containing crystals. The crystals druses, or solitary-prismatic.

Axial (stem, wood) anatomy. Secretory cavities absent. Cork cambium present; initially superficial (sub-epidermal). Primary vascular tissues in a cylinder, without separate bundles, or comprising a ring of bundles; collateral. Internal phloem absent. Medullary bundles present (in a Trigonia sp.?), or absent. Secondary thickening developing from a conventional cambial ring.

The wood diffuse porous. The vessels usually solitary. The vessel end-walls simple, or scalariform and simple. The vessels without vestured pits; without spiral thickening. The axial xylem with tracheids; with fibre tracheids; including septate fibres (rarely), or without septate fibres. The fibres with spiral thickening (rarely), or without spiral thickening. The parenchyma apotracheal, or apotracheal and paratracheal; wood not storied.

Reproductive type, pollination. Unisexual flowers absent. 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 units 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 (but 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, phytochemistry. 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 III core angiosperms; core eudicot; Superorder Rosanae; fabid. APG IV Order Malpighiales.

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

Illustrations. • Humbertiodendron saboureaui: Perrier de La Bathie and Leandri, Fl. de Madagascar et Comores 108 (1955). • Trigonia simplex, T. glazioviana: Nat. Pflanzenfam. III (1896). • Trigonia crotonoides: Lindley. • Trioniastrum hypoleucum: Fl. Malesiana 4 (1949).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 8th June 2026. delta-intkey.com’.

Contents