The families of flowering plants

L. Watson and M. J. Dallwitz

Tetracentraceae Van Tiegh.

~ Trochodendraceae.

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 (at least, with stipular flanges at the base of the petiole). Lamina margins serrate.

Leaf anatomy. The leaf lamina dorsiventral. Stomata present; paracytic, or tetracytic, or cyclocytic (‘laterocytic’). The mesophyll without sclerenchymatous idioblasts (but with large, branched idioblasts secreting resin).

Axial (stem, wood) anatomy. Young stems with solid internodes. Pith homogeneous (of pitted, relatively thick-walled cells). Cork cambium present; initially superficial. Nodes tri-lacunar. Primary vascular tissues in a cylinder, without separate bundles (the rays 1–3 cells wide); collateral. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. Primary medullary rays mixed wide and narrow. The axial xylem without vessels.

The axial xylem with tracheids; with fibre tracheids. The parenchyma apotracheal (diffuse). The secondary phloem stratified into hard (fibrous) and soft (parenchymatous) zones. ‘Included’ phloem absent. The wood not storied.

Reproductive type, pollination. 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, phytochemistry. 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.

General remarks. See Doweld (1998) for carpology and seed anatomy of Tetracentraceae and Trochodendraceae, discussion of taxonomic relationships, and relevant references. In terms of the present compilation, Tetracentron differs from Trochodendron in 35 characters, involving vegetative morphology and anatomy, sexuality of plants, numerous floral morphological features, etc., even perhaps in cytology.

Illustrations. • Technical details: Tetracentron (Hutchinson).

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: 19th October 2016.’.