Clematis subg. Clematis
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 year's 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.
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.
|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|