Trees deciduous [or evergreen], large, often buttressed, with soft wood, dioecious. Leaves alternate, long-petiolate; leaf blade simple, pubescent [or glabrous], lepidote, palmately 3-5-veined, margin entire or dentate. Inflorescences long, pendent spikes clustered at stem apices, male ones mostly branched, female ones usually simple [or axillary, solitary, simple spikes]. Bracts deciduous. Male flowers: calyx lobes 4-8, equal or unequal; petals absent [or 6-8, erect, greenish, narrowly triangular]; stamens 4-8, antesepalous; filaments elongate, somewhat flattened subulate; anthers basifixed, introrse or extrorse, incurved in bud, relatively short and ovoid, or if larger and ± oblong then conspicuously recurved; sterile ovary present or sometimes absent. Female flowers: calyx lobes 4-8, free or connate below ovary; petals and staminodes absent; ovary inferior, 1-loculed, with 4-8 parietal placentas; ovules numerous; styles 4-8, antesepalous, short, stout, with large, capitate or obliquely oblong-decurrent stigmas. Fruit a capsule, dehiscing apically between persistent styles [or shedding exocarp and dehiscing longitudinally]. Seeds numerous, ovoid or fusiform, tiny.
Two genera and two species: from India and Nepal through tropical SE Asia to Australia and the Solomon Islands; one species in China.
The other genus, Octomeles Miquel, comprises the single species O. sumatrana Miquel (O. moluccana Teijsmann & Binnendijk ex Hasskarl), which occurs in Indonesia, Malaysia (Sabah), New Guinea, the Philippines, and the Solomon Islands. It is a large tree like Tetrameles, but differs in the features enclosed in square brackets in the above description, as well as in having (5 or)6-8-merous flowers (vs. 4(or 5)-merous flowers in Tetrameles).
In the past, Octomeles and Tetrameles have been included together with Datisca Linnaeus to comprise the Datiscaceae. However, that group would be paraphyletic unless Begoniaceae were included. Therefore, two families are recognized here: Datiscaceae, comprising Datisca only, and Tetramelaceae, comprising the other two genera. Zhang et al. (Molec. Phylogen. Evol. 39: 305-322. 2006) placed Tetramelaceae as sister to Datiscaceae + Begoniaceae, although the latter clade had less than 50% support. The same authors placed Tetramelaceae + Datiscaceae + Begoniaceae as sister to Cucurbitaceae.
Datisca comprises two species: D. glomerata (C. Presl) Baillon, from W North America, and D. cannabina Linnaeus (including D. nepalensis D. Don). Datisca cannabina is a large, perennial, dioecious herb with pinnate leaves, and is distributed from the E Mediterranean (Crete) to the Himalayas, including countries adjoining W China from Kazakhstan to Nepal. It grows in moist places, often by streams in forests, and might yet be found in SW Xinjiang or SW Xizang.
Li Yanhui. 1999. Tetramelaceae. In: Ku Tsuechih, ed., Fl. Reipubl. Popularis Sin. 52(1): 123-125.