| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Tetramelaceae (Warb.) Airy Shaw

~ Datiscaceae.

Habit and leaf form. Large, often buttressed trees. Mesophytic. Leaves alternate; petiolate; non-sheathing; simple. Lamina entire; ovate; palmately veined; cross-venulate; cordate. Leaves exstipulate. Lamina margins entire, or dentate. Leaf development not ‘graminaceous’.

Leaf anatomy. The leaf lamina dorsiventral. Stomata present; on both surfaces (at least in Octomeles); anomocytic. Hairs present (Octomeles exhibiting scales, each with a 4-seriate stalk bearing a 1-layered circular shield with intact margin). Adaxial hypodermis present. The mesophyll with sclerenchymatous idioblasts (at least in Octomeles). Minor leaf veins without phloem transfer cells (Tetrameles).

Axial (stem, wood) anatomy. Secretory cavities absent. Cork cambium present; initially superficial. Primary vascular tissues in a cylinder, without separate bundles; collateral. Internal phloem absent. Cortical bundles absent. Medullary bundles absent. Secondary thickening developing from a conventional cambial ring.

The wood diffuse porous. The vessels large, or medium to large; solitary, radially paired, and in radial multiples, or in tangential arcs. The vessel end-walls simple. The vessels without spiral thickening. The axial xylem without fibre tracheids; with libriform fibres; including septate fibres, or without septate fibres. The fibres without spiral thickening. The parenchyma vasicentric or vasicentric to aliform paratracheal. The secondary phloem not stratified (but developing groups of fibres). The wood partially storied (VPI). Tyloses present, or absent.

Reproductive type, pollination. Fertile flowers functionally male, or functionally female. Unisexual flowers present. Plants dioecious. Female flowers without staminodes.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in spikes and in panicles. Inflorescences terminal, or axillary; terminal panicles or axillary, solitary spikes. Flowers regular to somewhat irregular. The floral irregularity when manifest, involving the perianth. Flowers cyclic. Free hypanthium present (“the corolla inserted on the calyx”).

Perianth with distinct calyx and corolla, or sepaline; 4, or 12–16; 1 whorled, or 2 whorled; isomerous. Calyx 4, or 6–8; 1 whorled; gamosepalous; unequal but not bilabiate, or regular; valvate. Corolla when present, 6–8; 1 whorled; polypetalous; valvate.

Androecium 4, or 6–8. Androecial members free of the perianth; free of one another; 1 whorled. Androecium exclusively of fertile stamens (in the male flowers). Stamens 4, or 6–8; isomerous with the perianth. Anthers dorsifixed; dehiscing via longitudinal slits; extrorse; bilocular. Pollen grains aperturate; 3 aperturate; colporate.

Gynoecium 4 carpelled, or 6–8 carpelled. Carpels isomerous with the perianth. The pistil 1 celled. Gynoecium syncarpous; synovarious; inferior. Ovary 1 locular. Gynoecium stylate. Styles 4, or 6–8; free; apical; thick, shorter than the ovary to much longer than the ovary. Stigmas 4–8; oblique or capitate. Placentation parietal. Ovules in the single cavity 20–100 (‘many’); pendulous to horizontal; anatropous; bitegmic.

Fruit non-fleshy; dehiscent; a capsule. Capsules valvular (the inner crustaceous-horny ovary wall sometimes breaking through the outer wall and the valves spreading stellately). Dispersal unit the seed. Fruit 20–100 seeded (‘many’). Seeds scantily endospermic, or non-endospermic (?); minute. Embryo straight.

Geography, cytology. Tropical. Southeast Asia, Malaysia, Australia. X = 11, 23 (or more).

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Myrtiflorae (?); Myrtales (? - cf. Lythraceae). Cronquist’s Subclass Dilleniidae; Violales. APG III core angiosperms; core eudicot; Superorder Rosanae; fabid. APG IV Order Cucurbitales.

Species 2. Genera 2; Tetrameles, Octomeles.

Illustrations. • Tetrameles nudiflora (as Tetramelis grahamiana): R. Wight, Ic. Pl. Indiae Orientalis 6 (1853).

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’.

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