The families of flowering plants

L. Watson and M.J. Dallwitz

Aristolochiaceae Juss.

Including Asaraceae Ventenat, Pipaceae Dulac, Pistolochinae (Pistolochiaceae) Link, Sarumaceae Nakai

Habit and leaf form. Shrubs, or lianas, or herbs (mostly woody vines); bearing essential oils. Plants green and photosynthesizing. Perennial; without conspicuous aggregations of leaves. Climbing, or self supporting (less often); mostly stem twiners. Mesophytic. Leaves alternate; spiral; flat; ‘herbaceous’, or ‘herbaceous’ and membranous; petiolate; sheathing to non-sheathing; gland-dotted (pellucid punctate), or not gland-dotted; aromatic; simple. Lamina entire (usually), or dissected; when dissected, palmatifid (trilobed); palmately veined, or pinnately veined; cross-venulate; often cordate. Leaves exstipulate (but sometimes with the first 1–2 leaves of the suppressed axillary branches simulating stipules); leaf development not ‘graminaceous’.

General anatomy. Plants with silica bodies, or without silica bodies.

Leaf anatomy. The leaf lamina dorsiventral (usually), or bifacial. Epidermis containing silica bodies, or without silica bodies. Stomata present; anomocytic. Hairs present; eglandular (mostly), or glandular (lacking typical glandular hairs, but hairs with basal secretory cells occur); multicellular. Multicellular hairs uniseriate; simple (but varied in form). The mesophyll with spherical etherial oil cells, or without etherial oil cells; containing crystals. The crystals raphides, druses, and solitary-prismatic. Minor leaf veins without phloem transfer cells (Aristolochia, Asarum).

Axial (stem, wood) anatomy. Cork cambium present; initially superficial. Nodes tri-lacunar. Primary vascular tissues comprising a ring of bundles; collateral. Internal phloem absent. Cortical bundles absent. Medullary bundles absent. Secondary thickening developing from a conventional cambial ring (but sometimes the pith and primary medullary rays are unusually dilated, the original vascular bundles becoming fan-shaped and deforming the secondarily thickened structure). Primary medullary rays very wide.

The wood ring porous to diffuse porous. The vessels small to large (very large in some twiners). The vessel end-walls simple. The vessels with spiral thickening, or without spiral thickening. The axial xylem with fibre tracheids, or without fibre tracheids; with libriform fibres, or without libriform fibres; including septate fibres. The fibres with spiral thickening, or without spiral thickening. The parenchyma apotracheal, or paratracheal.

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

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; when aggregated, in cymes, or in racemes, or in spikes. The ultimate inflorescence units 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; joined; 1 whorled, or 2 whorled (the corolla whorl conspicuous and well developed only in Saruma); when two-whorled, isomerous. Calyx 3; 1 whorled; gamosepalous; entire, or blunt-lobed; campanulate, or tubular (the tube often S-shaped); unequal but not bilabiate, or bilabiate, or regular; persistent, or not persistent; valvate (or valvate-induplicate). 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. Endothecium developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis successive, or simultaneous. The initial microspore tetrads tetrahedral, or isobilateral, or decussate, or T-shaped (rarely). Anther wall initially with more than one middle layer; of the ‘dicot’ type. Tapetum glandular. Pollen shed as single grains. Pollen grains aperturate, or nonaperturate; 1–7 aperturate; sulcate, or sulculate (monosulcate to multisulcoidate or sulculate); 2-celled.

Gynoecium 4–6 carpelled. Carpels isomerous with the perianth to increased in number relative to the perianth. The pistil 1 celled, or 4–6 celled. Gynoecium syncarpous; synovarious (Hexastylis), or synstylovarious, or eu-syncarpous; partly inferior (sometimes), or inferior (usually). Ovary 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); bitegmic; 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, or persistent. Synergids pear-shaped. Hypostase present. Endosperm formation cellular. Embryogeny probably solanad.

Fruit non-fleshy (usually), or fleshy (sometimes with a fleshy endocarp); dehiscent (usually), or indehiscent (rarely), or a schizocarp (Saruma). Mericarps in Saruma, 4–6 (?); 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. Embryo achlorophyllous (2/3).

Seedling. Germination phanerocotylar, or cryptocotylar.

Physiology, phytochemistry. Inulin recorded (Aristolochia, Gibbs 1974). Not cyanogenic. Alkaloids present (usually), or absent. Arbutin absent. Iridoids not detected. Proanthocyanidins absent. Flavonols present; quercetin, or kaempferol and quercetin. Ellagic acid absent (2 genera, 5 species). Aluminium accumulation not found. Sieve-tube plastids P-type; type I (a), or type II (a).

Geography, cytology. Temperate (warm), sub-tropical to tropical. Widespread, except Australasia. X = 4–7, 12, 13. Supposed basic chromosome number of family: 7.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Magnoliiflorae; Aristolochiales. Cronquist’s Subclass Magnoliidae; Aristolochiales. APG III core angiosperms; Superorder Magnolianae. APG IV Order Piperales.

Species 400. Genera 7; Apama, Aristolochia, Asarum, Euglypha, Holostylis, Saruma, Thottea.

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

Illustrations. • Aristolochia galeata: Lindley. • Aristolochia bracteata: Thonner. • Le Maout and Decaisne: Aristolochia. • Le Maout and Decaisne: Asarum. • Asarum caudigerum: Bot. Mag. 116 (1891). • Asarum maximum: Bot. Mag. 122 (1896). • Aristolochia chilensis Lindl.: Bot. Reg. 1680, 1835. • Aristolochia clematitis. • Aristolochia clematitis and Asarum europaeum: Eng. Bot. 1249 and 1250, 1868. • Aristolochia foetens Lindl.: Bot. Reg. 1824, 1836. • Stem sections of Aristolochia triangularis, showing anomalous anatomy (Solereder, 1908).

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: 15th April 2018.’.