Woody vines or erect, ± herbaceous perennials, clumped (or patch-forming from rhizomes in C. socialis). Leaves simple. Leaf blade 1- or 2-pinnate, ternate, or finely dissected; ultimate divisions lobed or unlobed, margins entire or few-toothed. Inflorescences terminal and/or axillary, on current year's stems; 3-7-flowered bracteate cymes or flowers solitary or paired, peduncles bracteate [or several-many-flowered panicles]. Flowers bisexual, usually nodding (± erect in some spp., esp. C. morefieldii); sepals ascending, connivent at least proximally and usually much of length, variously colored, lanceolate or oblong to broadly ovate, thick, usually leathery, abaxially glabrous to silky, hirsute, or tomentose; filaments slender, usually pubescent (except C. pitcheri var. dictyota), connectives often ± prolonged (especially in C. pitcheri); staminodes absent. Achenes flattened; beak variable in length, plumose to nearly glabrous.

Distribution

Temperate, mostly North America, a few in Eurasia.

Discussion

Species ca. 25 (18 in the flora).

Clematis integrifolia Linnaeus, with relatively wide-spreading, blue sepals, is locally naturalized in Ontario.

Selected References

Dennis, W. M. 1976. A Biosystematic Study of Clematis Section Viorna Subsection Viornae. Ph.D. dissertation. University of Tennessee.

Erickson, R. O. 1943. Taxonomy of Clematis section Viorna. Ann. Missouri Bot. Gard. 30: 1-62, plate 1.

Fernald, M. L. 1943. Morphological differentiation of Clematis ochroleuca and its allies. Rhodora 45: 401-412, figs. 776-782.

Keener, C. S. 1967. A biosystematic study of Clematis subsection Integrifoliae (Ranunculaceae). J. Elisha Mitchell Sci. Soc. 83: 1-41.

Lower Taxa

Clematis addisonii, Clematis albicoma, Clematis baldwinii, Clematis bigelovii, Clematis coactilis, Clematis crispa, Clematis fremontii, Clematis glaucophylla, Clematis hirsutissima, Clematis morefieldii, Clematis ochroleuca, Clematis pitcheri, Clematis reticulata, Clematis socialis, Clematis texensis, Clematis versicolor, Clematis viorna, Clematis viticaulis

Key

1	Leaves all simple, blade rarely so deeply lobed that proximal 2 lobes appear as distinct linear leaflets; plants herbaceous or ± woody at base, erect, not viny.	> 2
1	At least some distal leaves of main stems distinctly compound or deeply much-dissected; plants erect or viny.	> 8
2	Sepals glabrous or sparsely villous, tips acuminate; achene body cobwebby-tomentose distally, or long-pubescent.	> 3
2	Sepals (except margins) minutely puberulent, silky, woolly, or nearly glabrous, tips obtuse to acute; achene body pilose or short-pilose.	> 4
3	Leaf blade 3.5-11 cm wide, prominently reticulate adaxially; beak not plumose, proximally silky-tomentose, sparsely appressed-pubescent to nearly glabrous distally; Kans., Nebr., Mo.	Clematis fremontii
3	Leaf blade 0.2-2(-3.5) cm wide, not prominently reticulate adaxially; beak distinctly plumose; Fla.	Clematis baldwinii
4	Leaf blade abaxially moderately to densely soft-pubescent, rarely nearly glabrous; secondary and tertiary veins forming prominent reticulum on adaxial surface.	> 5
4	Leaf blade abaxially glabrous or nearly so, sparsely or rarely densely villous on veins; secondary and tertiary veins not forming prominent reticulum on adaxial surface.	> 6
5	Stems and abaxial surface of leaf blades moderately silky-pilose with spreading hairs, rarely nearly glabrous; beak yellowish brown to reddish brown; hairs of achene rim appressed-ascending.	Clematis ochroleuca
5	Stems and abaxial surface of leaf blades densely silky-tomentose with appressed hairs; beak white to pale yellow; hairs of achene rim spreading.	Clematis coactilis
6	Sepals abaxially silky to woolly; beak white to pale yellow.	Clematis albicoma
6	Sepals abaxially glabrous to minutely puberulent; beak coppery brown.	> 7
7	Leaf blade abaxially glaucous and glabrous; sepals abaxially glabrous.	Clematis addisonii
7	Leaf blade abaxially not glaucous, sparsely to densely villous on veins; sepals abaxially nearly glabrous or minutely puberulent.	Clematis viticaulis
8	Plants erect or sprawling, not viny; stems to 0.65m.	> 9
8	Plants viny, petioles and/or rachises of leaves often functioning as tendrils; stems usually 1-5m.	> 13
9	Larger leaf blades (1-)2-3-pinnate or -ternate or deeply dissected.	> 10
9	Leaf blade 1-pinnate or simple.	> 11
10	Leaflets usually less than 1.5 cm wide, mostly more than 2.5 times as long as wide, mostly unlobed, if lobed then with lateral lobes 1 or 2, usually small, distinctly narrower than central portion; blade abaxially sparsely to densely hirsute; beak plumose.	Clematis hirsutissima
10	Leaflets usually more than 1.5 cm wide and/or less than 2.5 times as long as wide, mostly lobed, lateral lobes often nearly as wide as central portion; blade glabrous or nearly so (rachis and petiolules may be ±hirsute); beak glabrous or inconspicuously appressed-pubescent.	Clematis bigelovii
11	Terminal leaflets usually tendril-like; blades of simple leaves and lateral leaflets of compound leaves usually more than 2 cm wide; sepals purple or reddish purple, whitish toward tips.	Clematis addisonii
11	Terminal leaflets with expanded blade, not tendril-like; blades of simple leaves and lateral leaflets usually less than 2 cm wide; sepals uniformly violet-blue.	> 12
12	Plants strongly rhizomatous, forming patches; sepals 2-2.5(-3) cm; beak 1.5-2.5 cm.	Clematis socialis
12	Plants not rhizomatous; sepals 2.5-5.5 cm; beak 6-10 cm.	Clematis baldwinii
13	Largest leaf blades 1-2-pinnate, leaflets mostly deeply lobed; beak 1-3 cm, inconspicuously appressed-pubescent to nearly glabrous.	Clematis pitcheri
13	Largest leaves simple, blades 1-pinnate, or if some 2-pinnate, leaflets of 2-pinnate leaves usually unlobed, rarely 2-5-lobed; beak 2-7 cm, plumose (appressed-puberulent in C.crispa and C.pitcheri).	> 14
14	Leaflets abaxially glaucous and glabrous, rarely with a few scattered hairs.	> 15
14	Leaflets not glaucous, usually abaxially pubescent, sometimes glabrous.	> 18
15	Leaves mostly simple, only distalmost compound.	Clematis addisonii
15	Leaves all or mostly compound, simple leaves, if any, only on small branches and near base of main stem.	> 16
16	Leaf blade ±thin, secondary and tertiary veins not forming prominent reticulum on adaxial surface.	Clematis glaucophylla
16	Leaf blade leathery, secondary and tertiary veins forming prominent reticulum on adaxial surface.	> 17
17	Sepals rose-red to scarlet abaxially and at tip adaxially; tips recurved.	Clematis texensis
17	Sepals pale lavender or blue-violet to reddish purple abaxially, often paler or greenish adaxially, tips slightly spreading.	Clematis versicolor
18	Sepals with thin, crispate margins to 6 mm wide distally.	Clematis crispa
18	Sepals without expanded, thin, crispate margins or with margins less than 2.5 mm wide.	> 19
19	Leaf blade leathery, secondary and tertiary veins forming prominent reticulum on adaxial surface.	> 20
19	Leaf blade thin, secondary and tertiary veins not forming prominent reticulum on adaxial surface.	> 21
20	Beak plumose, with spreading hairs; leaf blade finely reticulate (ultimate closed areoles mostly less than 2 mm in longer dimension), even quaternary veins distinctly raised on adaxial surface.	Clematis reticulata
20	Beak sparsely pubescent to silky, with ascending to appressed hairs; leaf blade less finely reticulate (ultimate closed areoles mostly more than 2 mm in longer dimension), tertiary and quaternary veins scarcely or not raised on adaxial surface.	Clematis pitcheri
21	Stems generally cobwebby as well as villous; bracts near base of peduncle/pedicel; sepals densely silky-pubescent abaxially, pinkish suffused with green, tips spreading to short-reflexed.	Clematis morefieldii
21	Stems without cobwebby pubescence; bracts well above base of peduncle/pedicel; sepals sparsely pubescent abaxially, pale lavender to reddish purple, tips recurved.	Clematis viorna