1 Flowers numerous, in compound cymose-paniculate inflorescences; sepals white; filaments glabrous; [subgenus Clematis].

  2 Flowers mostly polygamo-dioecious, the pistillate with 18-60 carpels; anthers 0.5-1 mm long; leaf margins coarsely toothed with acute teeth; leaflets 3 (C. virginiana) or 5-7 (C. catesbyana), uniformly green; [native, though sometimes weedy].

    3 Leaflets with terminal lobe (past last teeth) >2× as long as wide; plumose achene beak 4-9 cm long

    3 Leaflets with terminal lobe (past last teeth) <2× as long as wide; plumose achene beak 2.5-5 cm long

      4 Leaves (3-) 5-7-foliolate; pistillate flowers with 18-35 carpels

      4 Leaves 3-foliolate; pistillate flowers with 40-60 carpels

1 Flowers solitary or in groups of 3's; sepals usually at least partly bluish, purplish or red; filaments pubescent.

        5 Leaves (most or all of them) simple, sessile or subsessile; plant an erect herb to 7 dm tall; [subgenus Viorna].

          6 Leaves glaucous and glabrous beneath, the uppermost commonly pinnate and tendril-bearing

          6 Leaves green and usually pubescent beneath (glabrous in C. baldwinii), the uppermost usually simple and entire, neither pinnate nor tendril-bearing (though occasionally lobed).

             7 Leaves of flowering material soft-pubescent beneath, the largest 3-9 cm wide, with stomates on the lower surface only; leaves of fruiting material usually light green with the secondary and tertiary veins forming prominent reticulations on the upper surface.

               8 Stems and leaves usually densely sericeous-woolly; sepal backs densely sericeous; mature styles white to pale yellow, sharply recurved and flexuous; [of shale barrens and calcareous woodlands of w. VA]

               8 Stems and leaves villous; sepal backs moderately sericeous-pilose; mature styles yellowish-white to deep tawny, loosely spreading-recurved; [of various woodlands, fairly widespread in our area]

             7 Leaves of flowering material glabrous to sparsely pilose beneath, the largest 2-5 cm wide (or 3.5-11 cm wide in C. fremontii), with stomates on both surfaces; leaves of fruiting material often dark green, either with the secondary and tertiary veins forming prominent reticulations on the upper surface (C. fremontii) or the upper with the secondary and tertiary veins not forming prominent reticulations on the upper surface (C. albicoma, C. viticaulis, and C. baldwinii).

                 9 Sepal tips acuminate; achene bodies cobwebby-tomentose toward the tip (C. fremontii) or long pilose (C. baldwinii)

                   10 Leaf blades 0.2-2.5 (-3.5) cm wide, not notably reticulate on the upper surface; beak of the achene plumose with long hairs; [of wet pinelands of n. FL southward]

                   10 Leaf blades 3.5-11 cm wide, prominently reticulate on the upper surface; beak of the achene silky tomentose near the base, nearly glabrous toward the tip; [of prairies of nw. GA and se. TN, disjunct from further west]

                 9 Sepals tips obtuse to acute; achene bodies pilose throughout; [of shale barrens of w. VA and WV].

                     11 Sepal backs villous; pubescence on the summit of the achene and the base of the style spreading or reflexed; mature styles white to pale yellow, sharply recurved and flexuous

                     11 Sepal backs finely puberulent; pubescence on the summit of the achene and the base of the style closely appressed-ascending; mature styles tawny to deep reddish-brown, loosely spreading-recurved

        5 Leaves (most of them) compound, petiolate; plant a trailing or climbing vine or shrubby, to many meters long (or erect or ascending in C. addisonii and C. socialis).

                       12 Sepals thin in texture, 3-5 cm long, soft-villous, neither apically recurved nor with broad, strongly crisped margins; leaves 3-foliolate; [subgenus Atragene]

                       12 Sepals thick in texture, 1-5 cm long, short-sericeous, apically recurved; leaves 1-11-foliolate; [subgenus Viorna].

                          13 Lower surface of leaves glaucous and glabrous (rarely with a few scattered hairs).

                            14 Plant an erect or ascending herb; lower leaves simple, upper leaves simple to 2-6-foliolate; [of dry limestone glades, endemic to wc. VA]

                            14 Plant a climbing vine; all leaves generally compound, often 6-10-foliolate; [of various habitats, ranging from sw. VA, KY, TN, GA, and FL westwards].

                              15 Leaf blade thin in texture; secondary and tertiary veins impressed rather than raised on the upper leaflet surface

                              15 Leaf blade leathery in texture; secondary and tertiary veins forming a prominently raised reticulum on the upper leaflet surface.

                                16 Outer surface of sepals purplish-red or bluish-lavender towards the base and greenish or cream towards the tips; leaflets mostly ovate to elliptic, the base rounded to subcordate, the apex usually obtuse; [Interior Highlands of AR, MO, and OK and Interior Low Plateau of KY, TN, and AL]

                                16 Outer surface of sepals either bright scarlet red or yellowish-cream; leaflets mostly ovate to nearly circular in outline, the base mostly subcordate to deeply cordate, the apex often shallowly notched; [TX].

                                  17 Sepals yellowish-cream (sometimes lightly tinged with lilac); stamens densely and uniformly pubescent; [Carrizo Sands of ne. TX]

                                  17 Sepals bright scarlet red; stamens neither densely nor uniformly pubescent; [Edwards Plateau and northeastwards into the Lampasas Cutplain of c. TX]

                          13 Lower surface of leaves not glaucous, pubescent (rarely nearly glabrous).

                                    18 Plants erect, to 2-3 (-5) dm tall, forming clonal patches by underground rhizomes; leaflets linear-lanceolate, averaging ca. 10× as long as wide

                                    18 Plants viny, sprawling or climbing, the stems usually over 1 m long, not rhizomatous-clonal; leaflets generally broader.

                                       19 Leaves coriaceous, the secondary and tertiary veins forming prominent reticulations on the upper surface.

                                         20 Leaf blade coarsely reticulate-veined, the ultimate closed areoles often > 2 mm long in the longer dimension, the tertiary and quaternary veins not prominently raised; achene beak sparsely pubescent to silky, with ascending or appressed hairs

                                         20 Leaf blade finely reticulate-veined, the ultimate closed areoles mostly < 2 mm long in the longest dimension, the tertiary and quaternary veins often prominently raised; achene beak plumose, with spreading hairs

                                       19 Leaves membranous to subcoriaceous, the secondary and tertiary veins forming faint, indistinct reticulations on the upper surface.

                                           21 Sepals 2.5-5 cm long, the tips widely spreading, the upper margins thin, crisped, expanded (to 6 mm wide); sepal surfaces glabrous; [widespread, but mainly Coastal Plain]

                                           21 Sepals XX-YY cm long, the tips reflexed, the upper margins thick, not expanded; sepal surcaes glabrous to variously hairy; [widespread, but especially inland provinces].

                                             22 Principal leaves at mid-stem mostly pinnate, pubescent, slightly coriaceous with raised secondary and tertiary veins; inflorescence solitary in leaf axils, or cymose paniculate (1-3 flowered); sepals rarely solidly colored, sepals light pink, white, or bicolored; fruit compact; achene body orbicular in outline, the achene tails short recurvate; [open habitats (glades, barrens, blackbelt prairie remnants) over limestone]

                                             22 Principal leaves at mid-stem pinnately trifoliate, glabrous or glaucescent, membranous without raised secondary or tertiary veins; inflorescence solitary, terminal, or cymose-paniculate (3-7 flowered); sepals cherry red, magenta pink, or dusky purple; fruit less compact; achene body elliptical in outline, the achene tails long recurvate; [forested systems, forest/woodland ecotones, and grasslands]