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The families of flowering plants

L. Watson and M.J. Dallwitz

Picrodendraceae Small

~ Euphorbiaceae.

Habit and leaf form. Trees (with peeling bark); non-laticiferous. Leaves deciduous; alternate; long petiolate (the petioles without medullary bundles); non-sheathing; compound; ternate. Leaflets pulvinate (jointed at the base’). Lamina pinnately veined; cross-venulate. Leaves minutely stipulate. Stipules tiny and setiform, caducous, or persistent. Lamina margins entire.

Leaf anatomy. The leaf lamina with homogeneous, palisade-like mesophyll. Stomata present; mainly confined to one surface; paracytic.

Axial (stem, wood) anatomy. Secretory cavities absent. Internal phloem absent. Secondary thickening developing from a conventional cambial ring.

The vessel end-walls simple. The parenchyma apotracheal and paratracheal. ‘Included’ phloem absent.

Reproductive type, pollination. Fertile flowers functionally male, or functionally female. Plants dioecious. Female flowers without staminodes. Gynoecium of male flowers absent.

Inflorescence, floral, fruit and seed morphology. Flowers solitary (the female flowers, each on an apically expanded, long peduncle), or aggregated in ‘inflorescences’ (the male flowers); when solitary/female, axillary; male infloresences in panicles (narrow), or in catkins. Inflorescences of male flowers in strict catkinlike pseudoracemes or narrow thyrses. Flowers of male infloresences subtended by 3–7 imbricate bracts/bracteoles at the tips of their short pedicels, the solitary female flowers subtended only by the somewhat cupular peduncle expansion. Hypogynous disk absent (i.e., from the female flowers).

Perianth absent (in male flowers), or sepaline (in female flowers, unless interpreted as an involucre); of female flowers 4, or 5; 1 whorled. Calyx of female flowers 4, or 5; 1 whorled; polysepalous (the sepals lanceolate); unequal but not bilabiate; (sub-) valvate, or imbricate (scarcely so).

Androecium 20–70 (‘many’). Androecial members free of one another; borne on a hemispherical receptacle, loosely clustered and forming a globose head. Androecium of male flowers exclusively of fertile stamens. Stamens 20–70 (‘many’); shortly filantherous. Anthers dehiscing via longitudinal slits; ellipsoid, extrorse to latrorse; bilocular. Pollen grains aperturate; 5–8 aperturate; colporate (but the apertures not always strictly equatorial).

Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil 2 celled. Gynoecium syncarpous; synovarious to synstylovarious; superior (sic). Ovary 2 locular; sessile. Gynoecium stylate. Styles 1; attenuate from the ovary; apical. Stigmas 2 (thick, subulate, spreading). Placentation axile to apical. Ovules 2 per locule; pendulous (from a hemispherical placenta at the top of the loculus); arillate (with obturators); anatropous.

Fruit fleshy; indehiscent; a drupe (globular, with a thin, fleshy, orange pericarp containing numerous vesicles of bitter juice). The drupes with one stone (1–2 seeded, the indehiscent endocarp four-angled). Fruit 1–2 seeded. Seeds non-endospermic. Embryo well differentiated. Cotyledons 2 (much corrugated). Embryo bent (‘reflexed’).

Physiology, phytochemistry. Sugars transported as sucrose. Not cyanogenic. Iridoids not detected. Saponins/sapogenins absent.

Geography, cytology. Neotropical. Tropical. West Indies.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Malviflorae; Euphorbiales. Cronquist’s Subclass Rosidae; Euphorbiales. APG III core angiosperms; core eudicot; Superorder Rosanae; fabid. APG IV Order Malpighiales.

Species 3. Genera 1; only genus, Picrodendron.

General remarks. This description is confined to the monogeneric sensu stricto interpretation, cf. Airy Shaw (1973). The family has been extended by APG (2009) to include all 24 genera of the traditional Euphorbiaceae-Oldfieldioideae.

Illustrations. • Picrodendron baccatum: 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: 5th March 2018.’.