Herbs or lianas, perennial. Stems erect, twining, or procumbent. Leaves alternate, 2-ranked (evident on young growth, becoming obscure with age in some spec) stipules absent; pseudostipules absent [present]; petiole sometimes very short. Leaf blade membranous to leathery. Inflorescences on new growth or on older stems, axillary, racemes or solitary flowers; bracts present. Flowers: calyx usually mixture of purple, brown, green, or red, bilaterally symmetric, tubular, usually bent or curved, 1- or 3-lobed, not fleshy, base with utricle (basal, inflated portion of calyx surrounding or containing gynostemium); tube narrowed, sometimes extended proximally as cylindric syrinx (tubular or ringlike structure at juncture of tube and utricle, projecting into utricle cavity) and distally as annulus (circular flange at juncture of tube and limb) on limb; corolla absent; stamens 5-6, adnate to styles and stigmas, forming gynostemium; ovary inferior, 3-, 5-, or 6-locular; styles 3, 5, or 6, connate in column. Capsule dry, dehiscent. Seeds flattened or rounded, sometimes winged. x = 6, 7, 8.
Species ca. 300 (12 in the flora).
Most European and tropical species of Aristolochia are believed to be pollinated by small flies attracted to the flowers by the fetid odors and purple-brown color. Flies enter the flower when the stigmas are receptive and are trapped until after the anthers dehisce (H. Solereder 1889, 1889b). No formal studies of pollination of the North American species have been reported.
Many species of Aristolochia have been used in the treatment of snakebite; the treatment may or may not be effective. All species contain aristolochic acid, which is variously reported as tumor-causing or tumor-inhibiting (J. A. Duke 1985).
The leaves of many species are eaten by pipe-vine swallowtail butterflies. The larvae eat leaves of these species and sequester aristolochic acid in their bodies, making them unpalatable to birds (W. H. Howe 1975).
|1||Leaf base attentuate, cuneate, or truncate (truncate to slightly cordate in A. maxima).||> 2|
|1||Leaf base cordate, auriculate, sagittate, or hastate.||> 4|
|2||Woody lianas; peduncle not bracteolate; capsule 4-7 cm wide, dehiscence acropetal; syrinx absent.||Aristolochia maxima|
|2||Herbs; peduncle bracteolate; capsule 1-3 cm wide, dehiscence basipetal; syrinx present.||> 3|
|3||Inflorescences on new growth, axillary, solitary flowers; utricle ovoid to obconic; gynostemium 5-lobed; capsule ovoid.||Aristolochia erecta|
|3||Inflorescences from base of stem, racemes; utricle pear-shaped to ovoid; gynostemium 3-lobed; capsule globose.||Aristolochia serpentaria|
|5||Leaf venation palmate; calyx limb 1-lobed; young stem smooth; syrinx present; gynostemium 5-lobed.||Aristolochia pentandra|
|5||Leaf venation pinnate or palmate-pinnate; calyx limb 3-lobed; young stem ribbed; syrinx absent; gynostemium 3- or 6-lobed.||> 6|
|6||Leaf sinus 2-6 cm deep; capsule 1-3 cm wide; gynostemium 5-10 mm.||Aristolochia californica|
|6||Leaf sinus 1-4.5 cm deep; capsule 4-10 cm wide; gynostemium 1-4 mm.||> 7|
|7||Stem and leaf glabrous or puberulent; peduncle bracteolate; utricle globose to cylindric; annulus smooth.||Aristolochia macrophylla|
|7||Stem tomentose; leaves abaxially tomentose; peduncle not bracteolate; utricle globose to cylindric; annulus rugulose.||Aristolochia tomentosa|
|8||Leaf venation palmate; leaf blade as wide as long or wider.||> 9|
|8||Leaf venation pinnate or palmate-pinnate; leaf blade longer than wide.||> 11|
|9||Petiole 4-7 cm; stem erect; peduncle not bracteolate; gynostemium 3-lobed; young stem ribbed.||Aristolochia clematitis|
|9||Petiole 1-3 cm (to 4 cm in A. coryi); stem procumbent; peduncle bracteolate; gynostemium 5-lobed; young stem smooth or slightly striate.||> 10|
|10||Stem and leaf velutinous with yellowish trichomes; leaf blade ovoid to hastate, (0-)3-lobed; calyx brown-purple, straight; gynostemium ovoid.||Aristolochia wrightii|
|10||Stem and leaf glabrous or puberulent; leaf blade deltate, not 3-lobed; calyx yellow-green or yellow-brown, curved; gynostemium crown-shaped.||Aristolochia coryi|
|11||Leaf apex obtuse or rounded; gynostemium 5-10 mm; syrinx indistinct or absent.||Aristolochia reticulata|
|11||Leaf apex acuminate or acute; gynostemium 1-4 mm; syrinx present.||> 12|
|12||Calyx limb 1-lobed; inflorescences on new growth, axillary, solitary flowers; utricle ovoid to narrowly ellipsoid; gynostemium 5-lobed; capsule ovoid to obovoid; annulus absent on calyx limb.||Aristolochia watsonii|
|12||Calyx limb 3-lobed; inflorescences from base of stem, rarely an additional flower in axil of stem leaf, racemes; utricle pear-shaped to ovoid; gynostemium 3-lobed; capsule globose; annulus present on calyx limb, smooth.||Aristolochia serpentaria|