Cuscuta L.

Scientific Description

Family Cuscutaceae.

Habit and leaf form. Herbaceous climbers. Plants of very peculiar form (with threadlike, chlorophyll-less twining stems and short-lived root systems). Leaves much reduced (scale-like). Plants rootless (in that the normal root system is ephemeral); totally parasitic. On aerial parts of the host. Usually annual; plants with neither basal nor terminal concentrations of leaves. Climbing; stem twiners (with haustoria). Leaves minute; alternate; spiral; membranous; sessile; non-sheathing; simple; epulvinate. Leaf blades entire. Leaves without stipules. Stem anatomy. Secondary thickening absent.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in cymose clusters or spikes. Inflorescences simple, or compound; axillary. Flowers pedicellate to sessile; bracteate; small; regular to somewhat irregular. The floral asymmetry (when noticeable) involving the perianth (K only). Flowers (3–)5 merous; cyclic; tetracyclic. Free hypanthium absent. Perianth with distinct calyx and corolla; 6, or 8, or 10; 2 -whorled; isomerous. Calyx (3–)5; 1 -whorled; gamosepalous (shortly connate), or polysepalous (in some non-Australian species); imbricate; regular to unequal but not bilabiate (somewhat unequal); persistent. Corolla (3–)5; 1 -whorled; appendiculate (with lobed or fringed scales alternating with the stamens); usually gamopetalous (in lower half); imbricate, or valvate (?); tubular, or campanulate; regular; white, or pink. Androecium (3–)5, or (6–)10 (if the scales alternating with the stamens are interpreted as staminodes). Androecial members adnate (to the corolla tube); all equal; 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. Stamens (3–)5; isomerous with the perianth; oppositisepalous. Anthers dehiscing via longitudinal slits; tetrasporangiate. Pollen grains psilate. Gynoecium 2(–3) carpelled. The pistil 2(–3) celled. Gynoecium syncarpous; synovarious, or synstylovarious; superior. Ovary plurilocular; 2(–3) locular. Styles 2; free, or partially joined; apical. Stigmas 2; 1 - lobed; dry type; papillate; Group II type. Placentation basal. Ovules 2 per locule; ascending; anatropous.

Fruit and seed features. Fruit non-fleshy, or fleshy; dehiscent, or indehiscent (when fleshy); a capsule (ovoid to globular, lobed or unlobed). Capsules splitting irregularly (or opening by a transverse slit), or circumscissile (near the base). Fruit 4 seeded. Seeds endospermic. Endosperm oily. Cotyledons 0 (or scarcely recognisable as such). Embryo chlorophyllous; curved, or coiled.

Geography, cytology, number of species. World distribution: Cosmopolitan. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, South Australia, Northern Territory, Queensland, New South Wales, Victoria, Australian Capital Territory, and Tasmania. Northern Botanical Province, Eremaean Botanical Province, and South-West Botanical Province. X = 7, 15. A genus of 170 species; 7 species in Western Australia.

Additional characters Stigmas the stigmatic area linear, or globose (capitate or conic).