Family Cuscutaceae
Cuscutaceae Dum.~ Convolvulaceae Habit and leaf form. Parasitic herbs. Plants of very peculiar vegetative form; filamentous (with threadlike, chlorophyll-less twining stems and short-lived root systems). Leaves much reduced. Plants rootless (in that the normal root system is ephemeral); totally parasitic. Parasitic on aerial parts of the host. With neither basal nor terminal aggregations of leaves. Climbing; stem twiners (with haustoria). Leaves minute; alternate; spiral; membranous; sessile; non-sheathing; simple; epulvinate. Lamina entire. Leaves exstipulate. Leaf anatomy. Minor leaf veins without phloem transfer cells. Stem anatomy. Primary vascular tissue centrifugal. Secondary thickening absent. Xylem with vessels. Vessel end-walls simple. Reproductive type, pollination. Plants hermaphrodite. Inflorescence, floral, fruit and seed morphology. Flowers small; regular; (3–)5 merous; cyclic; tetracyclic. Free hypanthium absent. Perianth with distinct calyx and corolla; 6, or 10; 2 whorled; isomerous. Calyx (3–)5; 1 whorled; gamosepalous; imbricate. Corolla (3–)5; 1 whorled; appendiculate (with lobed or fringed scales alternating with the stamens); gamopetalous; valvate; regular; white, or pink. Androecium 5, or 10 (if the scales alternating with the stamens are interpreted as staminodes). Androecial members adnate (to the corolla tube); free of one another; 1 whorled, or 2 whorled (i.e. including the scales). Androecium exclusively of fertile stamens, or including staminodes (in the form of lobed or fimbriate scales). Staminodes 5; internal to the fertile stamens (antepetalous). Stamens 5; inserted in the throat of the corolla tube; isomerous with the perianth; oppositisepalous. Anthers dehiscing via longitudinal slits; tetrasporangiate. Endothecium developing fibrous thickenings. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or isobilateral, or decussate. Anther wall initially with one middle layer; of the ‘dicot’ type. Tapetum glandular. Pollen grains aperturate; 3–6 aperturate; colpate (including rupate); 3-celled. Gynoecium 2 carpelled. The pistil 2 celled. Gynoecium syncarpous; synovarious, or synstylovarious; superior. Ovary 2 locular. Styles 2; free, or partially joined; apical. Stigmas dry type; papillate; Group II type. Placentation basal. Ovules 2 per locule; ascending; anatropous; unitegmic; tenuinucellate. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Synergids beaked; haustorial (sometimes?), or non-haustorial. Endosperm formation nuclear. Embryogeny caryophyllad to solanad. Fruit non-fleshy, or fleshy; dehiscent; a capsule. Capsules splitting irregularly (or opening by a transverse slit). Seeds endospermic. Endosperm oily. Embryo rudimentary at the time of seed release to weakly differentiated (filiform). Cotyledons 0 (or scarcely recognisable as such). Embryo chlorophyllous (1/4); curved, or coiled, or other than straight, curved, bent or coiled (spiral). Seedling. Germination type inapplicable in the absence of cotyledons. Physiology, biochemistry. Cyanogenic (?), or not cyanogenic. Iridoids not detected. Proanthocyanidins present; cyanidin. Flavonols present; kaempferol and quercetin. Ellagic acid absent. Saponins/sapogenins present, or absent. Geography, cytology. Temperate to tropical. Cosmopolitan. Chromosomes with diffuse centromeres. X = 7, 15. Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Solaniflorae; Solanales. Cronquist’s Subclass Asteridae; Solanales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order Solanales (as a synonym of Convolvulaceae). Species 170. Genera 1; only genus, Cuscuta. Illustrations. |
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