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The families of flowering plants

L. Watson and M. J. Dallwitz

Droseraceae Salisb.

Including Adenaceae Dulac, Aldrovandraceae Nak., Dionaeeae (Dionaeaceae) Van Tiegh.; excluding Drosophyllaceae.

Habit and leaf form. Herbs. Plants with roots, or rootless (Aldrovandra); ‘carnivorous’. Trapping mechanism active. The traps constituted by sticky leaf glands, associated with subsequent, slow enclosure of the prey by movement of the blade (Drosera), or consisting of the curiously modified, steel-trap-like leaf blades, which spring shut when adaxial receptors are touched (Aldrovanda, Dionaea). With a basal aggregation of leaves (often), or without conspicuous aggregations of leaves; rhizomatous, or tuberous. Hydrophytic (Aldrovanda), or helophytic to mesophytic (usually in acid bogs); sometimes free floating (Aldrovanda). Leaves of Aldrovanda submerged. Leaves small to medium-sized; alternate (mostly), or whorled (Aldrovandra); spiral, or four-ranked; petiolate; non-sheathing; simple. Lamina entire. Leaves stipulate, or exstipulate; leaf development not ‘graminaceous’. Vernation often coiled inwards from the tip; circinnate (inwardly so, unlike the outwardly circinate leaves of Drosophyllum), or not circinnate.

Leaf anatomy. Minor leaf veins without phloem transfer cells (Dionaea, Drosera).

Axial (stem, wood) anatomy. Primary vascular tissues of the scape in a cylinder, without separate bundles (in Aldrovanda, reduced to a ring of phloem and a litte xylem parenchyma), or comprising a ring of bundles (e.g., in Drosera, where they tend to be centric), or comprising two or more rings of bundles (that of Drosophyllum having an exterior circle of small, widely spaced bundles, and a ring of three located more deeply). Secondary thickening absent.

Reproductive type, pollination. Unisexual flowers absent. Plants hermaphrodite. Pollination entomophilous.

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; when aggregated, in cymes. The ultimate inflorescence units cymose (usually). Inflorescences usually cincinni. Flowers regular; usually 4–5 merous; cyclic; tetracyclic, or pentacyclic. Floral receptacle with neither androphore nor gynophore. Free hypanthium present (slight), or absent. Hypogynous disk absent.

Perianth with distinct calyx and corolla; 8–10(–20); 2 whorled; isomerous. Calyx 4–5(–8); 1 whorled; scarcely gamosepalous, or polysepalous. Calyx lobes markedly longer than the tube. Calyx regular; persistent (marcescent); imbricate. Corolla 4–5(–12); 1 whorled; polypetalous; imbricate, or contorted; regular. Petals shortly clawed.

Androecium (4–)5 (usually), or 10–20 (rarely). Androecial members branched, or unbranched; free of the perianth; all equal; free of one another, or coherent; when cohering 1 adelphous (basally connate in Dionaea); 1 whorled, or 2 whorled. Androecium exclusively of fertile stamens. Stamens (4–)5, or (10–)20; isomerous with the perianth to triplostemonous. Anthers dorsifixed, or basifixed; dehiscing via longitudinal slits; extrorse; tetrasporangiate. Endothecium developing fibrous thickenings. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or isobilateral. Anther wall initially with one middle layer; of the ‘monocot’ type. Tapetum glandular, or amoeboid. Pollen shed in aggregates; in tetrads. Pollen grains aperturate; 3–50 aperturate (?); colpate, or porate, or foraminate; 2-celled (Dionaea), or 2-celled and 3-celled (with both conditions in Drosera).

Gynoecium 3(–5) carpelled. The pistil 1 celled. Gynoecium syncarpous; synovarious, or synstylovarious; superior. Ovary 1 locular. The ‘odd’ carpel when G3 posterior. Gynoecium stylate. Styles 1, or 3(–5); free, or partially joined; apical. Stigmas often 2 lobed; dry type; papillate; Group II type. Placentation parietal, or basal. Ovules in the single cavity 3–100 (i.e. to ‘many’); ascending; non-arillate; anatropous; bitegmic; tenuinucellate, or crassinucellate. Outer integument not contributing to the micropyle. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids hooked (with filiform apparatus). Endosperm formation nuclear. Embryogeny caryophyllad to solanad, or onagrad to asterad.

Fruit non-fleshy; dehiscent (nearly always), or indehiscent (Aldrovandra); a capsule (usually), or capsular-indehiscent (Aldrovandra). Capsules loculicidal, or valvular. Seeds copiously endospermic. Endosperm oily. Seeds winged, or wingless. Seeds with starch. Embryo well differentiated (small). Cotyledons 2. Embryo straight.

Seedling. Germination phanerocotylar, or cryptocotylar.

Physiology, phytochemistry. C3. C3 physiology recorded directly in Dionaea. Inulin recorded (Gibbs 1974). Cyanogenic (mostly), or not cyanogenic. Alkaloids absent (one species). Iridoids not detected. Saponins/sapogenins absent. Proanthocyanidins present; cyanidin and delphinidin. Flavonols present; kaempferol and quercetin. Ellagic acid present (Drosera, 2 species). Aluminium accumulation not found.

Geography, cytology. Frigid zone to tropical. Widespread. X = 6–17(+).

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Theiflorae; Droserales. Cronquist’s Subclass Dilleniidae; Nepenthales. APG 3 core angiosperms; core eudicot; Superorder Caryophyllanae; Order Caryophyllales.

Species about 110. Genera 3; Dionaea, Aldrovanda, Drosera.

Illustrations. • Technical details: Drosera rotundifolia, D. anglica. • Drosera stenopetala: Hooker, Fl. Novae-Zelandiae (1853). • Technical details: Dionaea. • Dionaea muscipula (Nat. Misc. 40, 1790). • Drosera rotundifolia, D. anglica and D. intermedia: Eng. Bot. 182–184, 1864. • Drosera anglica (B. Ent.). • Some Drosera spp. from SW Australia (photos). • Aldrovanda, Dionaea, Drosera, Drosophyllum (Drosophyllaceae): leaf hairs and enations (Solereder, 1908).

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: 22nd August 2016.’.