Woody vines (erect, herbaceous perennials in C. recta). Leaf-blade 1-2-pinnate; leaflets lobed or unlobed, margins entire or toothed. Inflorescences terminal and/or axillary on current-years stems, cymes or panicles or flowers solitary or paired, bracteate. Flowers bisexual, or unisexual with staminate and pistillate on different plants, not nodding, or ± nodding in yellow-flowered species; perianth rotate; sepals spreading, not connivent, linear, oblong, elliptic, lanceolate, ovate, oblanceolate, or obovate, thin and white or somewhat thickened and yellow; filaments filiform, slender, glabrous or pubescent; staminodes absent from staminate flowers, usually present in pistillate flowers; pistils rudimentary or absent in staminate flowers. Achenes flattened or nearly terete; beak more than 1.5 cm, plumose.
Distribution
Worldwide
Discussion
Species 50-100 (11 in the flora).
The Asian (Korean) species Clematis serratifolia Rehder, with light yellow sepals and purple stamens, may also escape from cultivation and spread locally.
Selected References
None.
Lower Taxa
Key
| 1 | Sepals greenish yellow to bright yellow, ascending or wide-spreading and recurved. | > 2 |
| 1 | Sepals white to cream, wide-spreading, not recurved. | > 3 |
| 2 | Leaflet margins entire or coarsely few-toothed; sepals greenish yellow, pubescent or abaxially glabrous. | Clematis orientalis |
| 2 | Leaflet margins serrate; sepals bright yellow, adaxially glabrous. | Clematis tangutica var. tangutica |
| 3 | Flowers bisexual. | > 4 |
| 3 | Flowers unisexual. | > 6 |
| 4 | Stems herbaceous, not viny. | Clematis recta |
| 4 | Stems ±woody, climbing with tendril-like petioles and rachises of compound leaves. | > 5 |
| 5 | Pistils 10 or fewer per flower; achenes flattened, with conspicuous rims. | Clematis terniflora |
| 5 | Pistils 20 or more per flower; achenes nearly terete, without conspicuous rims. | Clematis vitalba |
| 6 | Leaflets deltate to ovate, strongly 3-parted to 3-sect, segments ovate, deltate, or linear; achene with beak 4–9 cm; sw United States, Mexico. | Clematis drummondii |
| 6 | Leaflets ovate to lanceolate, variously lobed or toothed, but without narrow segments; achene with beak to 5.5 cm. | > 7 |
| 7 | Flowers solitary (rarely 3 in simple cymes); pedicel (or peduncle and pedicel combined for solitary flowers) stout, 3.5 cm or more; pistils 75–100 per flower. | Clematis lasiantha |
| 7 | Flowers (1–)3 or more, in simple or compound cymes or in panicles, occasionally solitary in C.pauciflora; pedicel slender, less than 3.5 cm; pistils fewer than 70 per flower. | > 8 |
| 8 | Achene body broadly ovate to nearly orbiculate, glabrous; sepals hairy only abaxially; leaflets to 3.5 cm. | Clematis pauciflora |
| 8 | Achene body ovate, pubescent; sepals hairy on both surfaces; leaflets usually longer than 3 cm. | > 9 |
| 9 | Leaf blade 3-foliolate. | Clematis virginiana |
| 9 | Leaf blade pinnately 5-foliolate to 2-pinnate. | > 10 |
| 10 | Inflorescences compound cymes, often distinctly corymbiform, flowers crowded; pistils 25–65 per flower; leaf blade somewhat succulent, ultimate venation obscure; w North America. | Clematis ligusticifolia |
| 10 | Inflorescences panicles, not usually corymbiform or with flowers crowded; pistils 18–35 per flower; leaf blade membranous, ultimate venation conspicuous; primarily e North America. | Clematis catesbyana |
"thin" is not a number.