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The families of flowering plants.                                                                                                                                                                

Droseraceae Salisb.

                        

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IncludingAdenaceae 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 with neither basal nor terminal 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; without a persistent basal meristem. Vernation often circinnate; circinnate (inwardly so, unlike the outwardly circinate leaves of Drosophyllum), or not circinnate.

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

Stem anatomy. Secondary thickening absent.

Reproductive type, pollination. Unisexual flowersabsent. Plants hermaphrodite. Pollination entomophilous.

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; in cymes. The ultimate inflorescence unit 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.

Perianthwith 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. Pollenshed 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. Ovary1 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, biochemistry. Cyanogenic (mostly), or not cyanogenic. Alkaloids absent (one species). Iridoids not detected. Proanthocyanidins present; cyanidin and delphinidin. Flavonols present; kaempferol and quercetin. Ellagic acid present (Drosera, 2 species). Saponins/sapogenins absent. Aluminium accumulation not found. Inulin recorded (Gibbs 1974). C3. C3 physiology recorded directly in Dionaea.

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.
  • 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).
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