Tetracentraceae Van Tiegh.
Habit and leaf form. Trees (with short-shoots on slender branches, each short-shoot bearing a single leaf). Leaves deciduous; petiolate; simple. Lamina entire; ovate; palmately veined; cordate. Leaves stipulate (with stipular flanges at the base of the petiole). Lamina margins serrate.
Leaf anatomy. Stomata present; paracytic, or tetracytic (‘laterocytic’).
Lamina dorsiventral. The mesophyll without sclerenchymatous idioblasts (but with large, branched idioblasts secreting resin).
Stem anatomy. Cork cambium present; initially superficial. Nodes tri-lacunar. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent. Xylem with tracheids; with fibre tracheids; without vessels. Wood parenchyma apotracheal (diffuse).
Reproductive type, pollination. Fertile flowers hermaphrodite. Plants hermaphrodite. Floral nectaries present. Nectar secretion from the gynoecium (from the carpel surface). Pollination anemophilous.
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in spikes (catkin-like). Inflorescences subterminal on the short-shoots; pendulous, catkin-like spikes, with flowers in groups of four. Flowers bracteate; bracteolate (as represented by the outer pair of ‘tepals’), or ebracteolate (if so interpreted); very small; regular; 4 merous; cyclic; tricyclic (if the outer pair of ‘perianth’ members are interpreted as bracteoles), or tetracyclic. Free hypanthium absent. Hypogynous disk absent.
Perianth sepaline (petals absent); ostensibly 4; ostensibly 2 whorled (i.e. two decussate pairs), or 1 whorled (if the outer perianth is interpreted as bracteoles). Calyx ostensibly 4; ostensibly 2 whorled; polysepalous (the members weakly vascularized); regular; imbricate.
Androecium 4. Androecial members free of the perianth; all equal; free of one another; 1 whorled, or 2 whorled (on close scrutiny). Androecium exclusively of fertile stamens. Stamens 4; isomerous with the perianth; ostensibly oppositisepalous (and alternating with the carpels); erect in bud; filantherous (the filaments slender). Anthers basifixed; non-versatile; dehiscing by longitudinal valves (each theca dehiscing by two valves, cf. Trochodendron); latrorse; tetrasporangiate. Pollen shed as single grains. Pollen grains aperturate; 3 aperturate; colpate, or colporate (cop(oroid)ate); 2-celled.
Gynoecium 4 carpelled. Carpels isomerous with the perianth. The pistil basally 4 celled. Gynoecium apocarpous to syncarpous; semicarpous (the whorl of four carpels connate laterally at the bases, distinct distally); superior. Carpel stylate (the style short, ventrally terminal); apically stigmatic (the stigma decurrent); 5–6 ovuled. Placentation marginal. Ovary basally 4 locular. Ovules pendulous; anatropous; bitegmic; crassinucellate. Outer integument not contributing to the micropyle. Endosperm formation cellular.
Fruit non-fleshy; more or less an aggregate (a ‘follicetum’), or not an aggregate (according to interpretation). The fruiting carpel dehiscent; a follicle (the follicles laterally coherent, if thus interpreted). Fruit if considered syncarpous, dehiscent; a capsule (‘a ventrihescent capsule'). Seeds endospermic. Endosperm oily (and proteinaceous). Seeds with a testa (thin). Embryo rudimentary at the time of seed release to weakly differentiated (minute, sometimes with two rudimentary cotyledons). Embryo straight. Testa brown, or yellow. Micropyle not zigzag (rudimentary).
Physiology, biochemistry. Not cyanogenic. Iridoids not detected. Proanthocyanidins present; cyanidin. Flavonols present; quercetin. Ellagic acid absent.
Geography, cytology. Sub-tropical to tropical. Northeast India, Burma, Southwest China. 2n = 46 or 48.
Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Rosiflorae; Trochodendrales. Cronquist’s Subclass Hamamelidae; Trochodendrales. APG 3 core angiosperms; peripheral eudicot; Superorder Proteanae; Order Trochodendrales (as a synonym of Trochodendraceae).
Species 1. Genera 1; only genus, Tetracentron.
See Doweld (1998) for carpology and seed anatomy of Tetracentraceae and Trochodendraceae, discussion of taxonomic relationships, and recent relevant references.