Aristolochiaceae Juss.

Scientific Description

Common name. Birthwort Family.

Habit and leaf form. Shrubs, or lianas, or herbs (mostly woody vines); bearing essential oils. Perennial; plants with neither basal nor terminal concentrations of leaves. Climbing, or self supporting (less often); mostly stem twiners. Mesophytic. Leaves alternate; spiral; ‘herbaceous’, or ‘herbaceous’ and membranous; petiolate; sheathing to non-sheathing; gland-dotted (pellucid punctate), or not gland-dotted; aromatic; simple. Leaf blades entire (usually), or dissected; flat; when dissected, palmately lobed (trilobed); palmately veined, or pinnately veined; cross-venulate; often cordate. Leaves without stipules (but sometimes with the first 1–2 leaves of the suppressed axillary branches simulating stipules); without a persistent basal meristem. Stem anatomy. Nodes tri-lacunar. Secondary thickening developing from a conventional cambial ring (but sometimes the pith and primary medullary rays are unusually dilated, deforming the secondarily thickened structure).

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous; via diptera. Pollination mechanism conspicuously specialized (via an elaborate system for trapping flies within the perianth tube, involving articulated hairs which subsequently wither to release them).

Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; in cymes, or in racemes, or in spikes. The terminal inflorescence unit cymose, or racemose. Inflorescences terminal, or axillary; terminal or lateral racemes or cymes. Flowers small to large; often malodorous (smelling of carrion), or odourless; regular to very irregular; cyclic; tricyclic to pentacyclic. Perianth with distinct calyx and corolla, or petaline; 3, or 6; 1 -whorled, or 2 -whorled (the corolla whorl conspicuous and well developed only in Saruma); when two-whorled, isomerous; joined. Calyx 3; 1 -whorled; gamosepalous; entire, or lobed; when lobed, blunt-lobed; valvate (or valvate-induplicate); campanulate, or tubular (often S-shaped); unequal but not bilabiate, or bilabiate, or regular; persistent, or not persistent. Corolla when present, 3 (usually reduced or absent); 1 -whorled. Androecium 6–36. Androecial members free of the perianth; united with the gynoecium (forming a gynostemium by fusion to the style of the filaments, or of both the filaments and the anthers), or free of the gynoecium; free of one another, or coherent (via the gynostemium); when joined, 1 - adelphous; 1 -whorled, or 2 -whorled. Androecium exclusively of fertile stamens. Stamens 4, or 6 (commonly), or 12(–36); isomerous with the perianth to polystemonous; filantherous, or with sessile anthers. Anthers cohering, or separate from one another; basifixed, or adnate; non-versatile; dehiscing via longitudinal slits; extrorse, or extrorse and introrse (Heterotropa); tetrasporangiate; appendaged (apically, with the expanded connective assuming stigmatic functions in association with the gynostemium), or unappendaged. Pollen shed as single grains. Gynoecium 4–6 carpelled. The pistil 4–6 celled, or 1 celled. Carpels isomerous with the perianth to increased in number relative to the perianth. Gynoecium syncarpous; synovarious (Hexastylis), or synstylovarious, or eu-syncarpous; partly inferior (sometimes), or inferior (usually). Ovary unilocular, or plurilocular; 4–6 locular, or 1 locular (the septa sometimes incompletely intruded). Epigynous disk present, or absent. Gynoecium stylate. Styles 1, or 4–6; free, or partially joined; apical. Stigmas dry type (mostly), or wet type; papillate; Group II type, or Group III type. Placentation when unilocular, parietal; when plurilocular, axile. Ovules in the single cavity when unilocular, 50–100 (‘many’); when plurilocular, 20–50 per locule (‘many’); funicled; pendulous, or horizontal; anatropous (or circinotropous).

Fruit and seed features. Fruit non-fleshy (usually), or fleshy (sometimes with a fleshy endocarp); dehiscent (usually), or indehiscent (rarely), or a schizocarp (Saruma). Mericarps in Saruma, comprising follicles. Fruit a capsule (usually), or a berry, or a nut. Capsules when dehiscent, septicidal and valvular (usually basally, rarely at the top), or splitting irregularly. Seeds endospermic. Endosperm ruminate, or not ruminate; oily. Embryo rudimentary at the time of seed release to weakly differentiated; achlorophyllous (2/3). Seedling. Germination phanerocotylar, or cryptocotylar.

Physiology, biochemistry. Aluminium accumulation not found.

Geography, cytology, number of species. World distribution: widespread, except Australasia. X = 4–7, 12, 13. 400 species.

Economic uses, etc. A few Aristolochia and Asarum spp. cultivated as ornamentals.