The families of flowering plants

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L. Watson and M. J. Dallwitz

Roridulaceae Engl. & Gilg

~ Byblidaceae.

Habit and leaf form. Shrublets or small shrubs. Plants curiously, indirectly ‘carnivorous’ (q.v.). Trapping mechanism passive. The traps consisting of the sticky-glandular, non-irritable (flypaper-like) leaves (with stalked, capitate, viscous-glandular tentacles of various lengths. The sticky exudate entraps insects, but contains no digestive enzymes: the captives are eaten by a specialized hemipteran bug, whose nutritious excretions are absorbed by the plant through its leaves (Ellis and Midgely 1996, Oecologia 106, 478)). Leaves alternate; simple. Lamina dissected, or entire; linear to lanceolate; when dissected, pinnatifid. Leaves exstipulate. Vernation coiled inwards from the tip; circinnate.

Leaf anatomy. The leaf lamina dorsiventral. Stomata present; mainly confined to one surface (abaxial); anomocytic.

Axial (stem, wood) anatomy. Primary vascular tissues comprising a ring of bundles; collateral. Secondary thickening absent, or developing from a conventional cambial ring (?). Primary medullary rays narrow (mostly uniseriate).

The vessels solitary. The vessel end-walls scalariform (with many bars). The vessels with spiral thickening. The axial xylem with libriform fibres. The parenchyma apotracheal.

Reproductive type, pollination. Plants hermaphrodite. Pollination entomophilous; by small Heteroptera; mechanism conspicuously specialized (the sensitive stamens springing suddenly upright to scatter pollen over visiting insects).

Inflorescence, floral, fruit and seed morphology. Flowers solitary (axillary, according to Airy Shaw 1973), or aggregated in ‘inflorescences’ (in terminal racemes, according to Cronquist); if solitary, axillary; (bi-) bracteolate; regular; 5 merous; cyclic; tetracyclic. Free hypanthium absent.

Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; gamosepalous (basally connate); blunt-lobed, or toothed; regular; persistent; imbricate. Corolla 5; 1 whorled; gamopetalous (shortly connate basally). Corolla lobes markedly longer than the tube. Corolla imbricate; regular (the lobes broad-elliptic, acute).

Androecium 5. Androecial members adnate (to the base of the corolla); all equal; free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 5; isomerous with the perianth; oppositisepalous; alternating with the corolla members; inflexed in bud; filantherous. Filaments thickened at the base. Anthers basifixed; becoming inverted during development, their morphological bases ostensibly apical in the mature stamens; apically dehiscing via pores, or dehiscing via short slits; extrorse; bilocular; tetrasporangiate. Pollen grains aperturate; 3 aperturate; sulculate (colporoidate).

Gynoecium 3 carpelled. Carpels reduced in number relative to the perianth. The pistil 3 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary 3 locular; sessile. Gynoecium shortly stylate. Styles 1; apical. Stigmas 1; capitate. Placentation axile to apical. Ovules 1–6 per locule (to ‘several’); pendulous; anatropous; unitegmic, or bitegmic; tenuinucellate.

Fruit non-fleshy; dehiscent; a capsule. Capsules septicidal and loculicidal (the three loculicidal and semiseptiferous valves separated from the persistent columella). Seeds copiously endospermic (the endosperm fleshy); medium sized to large (‘rather large’); with a testa (this crustaceous, areolate). Embryo well differentiated (but small). Cotyledons 2. Embryo straight.

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. Not cyanogenic. Iridoids detected; ‘Route I’ type (+seco). Proanthocyanidins absent.

Geography, cytology. Cape. Sub-tropical to tropical. South Africa.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Corniflorae; Ericales. Cronquist’s Subclass Rosidae; Rosales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; Order Ericales.

Species 2. Genera 1; only genus, Roridula.

General remarks. This compilation on ‘tentacular glands’ (hairs or enations?), embryology, etc., is inadequate — Lloyd not yet consulted).

Illustrations. • Roridula dentata: Nat. Pflanzenfam. III (1891).

The descriptions are offered for casual browsing only. We strongly advise against extracting comparative information from them. This is much more easily achieved using 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).

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 16th May 2016.’.