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The families of flowering plants

L. Watson and M. J. Dallwitz

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. Without conspicuous aggregations of leaves. Climbing; stem twiners (with haustoria). Leaves minute; alternate; spiral; membranous; sessile; non-sheathing; simple; epulvinate. Lamina entire. Leaves exstipulate.

Leaf anatomy. Hairs present, or absent; unicellular, or multicellular (mostly simple, of one or two cells). Minor leaf veins without phloem transfer cells.

Axial (stem, wood) anatomy. Primary vascular tissues much reduced, in a cylinder, without separate bundles to comprising a ring of bundles (comprising minute groips of vessels accompanied by phloem strands, either constituting a closed ring or more widely separated); collateral. Internal phloem absent. Secondary thickening absent.

The vessel end-walls simple.

Reproductive type, pollination. Fertile flowers hermaphrodite. 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, phytochemistry. Cyanogenic (?), or not cyanogenic. Iridoids not detected. Saponins/sapogenins present, or absent. Proanthocyanidins present; cyanidin. Flavonols present; kaempferol and quercetin. Ellagic acid 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.

General remarks. These compiled descriptions show 12 differences between Cuscuta and Convolvulaceae (q.v.) in floral morphology, embryology, phytochemistry and cytology, additional to characters directly associated with the parasitic habit.

Illustrations. • Technical details: Cuscuta. • Technical details: Cuscuta (Lindley). • Cuscuta epithymum (on Calluna, B. Ent.). • Cuscuta epilinum: Eng. Bot. 926, 1866. • Cuscuta europaea: Eng. Bot. 927, 1866. • Cuscuta epithymum: Eng. Bot. 928, 1866.

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or 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). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 19th October 2016.’.