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The families of flowering plants

L. Watson and M. J. Dallwitz

Didiereaceae Radlk. ex Drake

Habit and leaf form. Trees, or shrubs (with spiny short-shoots in the leaf axils of the long-shoots). Switch-plants; with the principal photosynthesizing function transferred to stems and ‘cactoid’, with succulent, photosynthetic stems (or ‘euphorbioid’). Leaves well developed (but small), or much reduced. Plants succulent (the younger long-shoots succulent, becoming woody with age, the short-shoots spiny). Leaves small; alternate; simple. Lamina entire. Leaves exstipulate.

Leaf anatomy. The leaf lamina more or less dorsiventral, or bifacial (sometimes exhibiting a weak palisade). The mesophyll containing mucilage cells. Minor leaf veins without phloem transfer cells (Alluaudia).

Axial (stem, wood) anatomy. Secretory cavities present (in the cortex); with mucilage. Primary vascular tissues more or less comprising a ring of bundles (comprising an almost closed arc or 7–9 bundles); collateral. Internal phloem absent. Cortical bundles absent. Medullary bundles absent. Secondary thickening developing from a conventional cambial ring. Primary medullary rays wide.

The wood diffuse porous. The vessels solitary, in radial multiples, and clustered (with irregular clusters and groups of mutiples). The vessel end-walls simple. The vessels without vestured pits; without spiral thickening. The axial xylem with libriform fibres; without septate fibres. The fibres without spiral thickening. The parenchyma paratracheal (scanty and terminal). ‘Included’ phloem absent. The wood not storied.

Reproductive type, pollination. Plants dioecious, or gynomonoecious. Female flowers with staminodes, or without staminodes.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in cymes. The ultimate inflorescence units cymose. Inflorescences terminal (on the long- and short-shoots); more or less dichasial cymes. Flowers cyclic. Hypogynous disk present; intrastaminal; annular.

Perianth with distinct calyx and corolla (though the petaline ‘calyx’ could be interpreted as bracteoles, the ‘corolla’ as sepals); 6; 3 whorled; isomerous. Calyx 2; 1 whorled; polysepalous (petaloid, decussate); persistent. Corolla 4; 2 whorled (2+2, decussate); polypetalous. Petals sessile.

Androecium 8(–10). Androecial members free of the perianth; free of one another (weakly adnate to the outside of the nectary); 2 whorled. Androecium exclusively of fertile stamens. Stamens 8(–10); filantherous (the filaments woolly). Anthers dorsifixed; dehiscing via longitudinal slits; introrse; tetrasporangiate. Pollen grains aperturate; (4–)5–7 aperturate; colpate (but occasionally with one or two pores near the poles in addition to the furrows); spinulose; 3-celled.

Gynoecium (2–)3(–4) carpelled. Carpels isomerous with the perianth, or increased in number relative to the perianth. The pistil (2–)3(–4) celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior. Ovary (2–)3(–4) locular (but only the medial-adaxial one fertile, the others empty). Gynoecium stylate. Styles 1; attenuate from the ovary; apical. Stigmas (2–)3(–4). Placentation basal. Ovules 1 per locule; ascending; apotropous; with ventral raphe; arillate; campylotropous; bitegmic; crassinucellate. Endosperm formation nuclear.

Fruit non-fleshy; indehiscent; capsular-indehiscent (three-angled); 1 seeded (the seed with a small funicular aril). Seeds nearly non-endospermic. Embryo well differentiated. Cotyledons 2 (these fleshy). Embryo curved, or bent.

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. CAM. CAM recorded directly in Alluaudia, Alluaudiopsis, Decaryia, Didieria. Not cyanogenic. Iridoids not detected. Betalains present. Proanthocyanidins present. Sieve-tube plastids P-type; type III (a).

Geography, cytology. Paleotropical. Tropical. In semi-desert parts of Madagascar. Ploidy levels recorded: seemingly high — 2n=150, 190–200.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Caryophylliflorae; Caryophyllales. Cronquist’s Subclass Caryophyllidae; Caryophyllales. APG 3 core angiosperms; core eudicot; Superorder Caryophyllanae; Order Caryophyllales.

Species 11. Genera 4; Didierea, Alluaudia, Alluaudiopsis, Decaryia.

Illustrations. • Technical details: Didierea (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.’.