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Key to Clematis

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1 Flowers numerous, in compound cymose-paniculate inflorescences; sepals white; filaments glabrous; [subgenus Clematis].
..2 Flowers perfect, with 5-10 carpels; anthers 1.5-3 mm long; leaf margins entire (rarely cleft or with 1-2 rounded teeth or small lobes); leaflets (3-) 5 (-7), often variegated with a silver blaze along the midvein; [alien, in disturbed areas]
..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]

Key A: Clematis reticulata complex

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1 Plants an erect-ascending herb in flower, becoming scandent in late season; primary inflorescences always terminal, solitary, ebracteate (occasional axillary and bracteate in late season); proximal-most leaflets (those closest to the stem) of mid-stem leaves sessile or short-petiolulate, the petiolules 3.1-9.4 (-10.3) mm long; [endemic to the Pine Mountain Ridges of wc. GA]
1 Plants vining in habit throughout season; primary inflorescences axillary; proximal-most leaflets (those closest to the stem) of mid-stem leaves usually long-petiolulate, the petiolules (5.5-) 16.9–22.7 (-49.0) mm long.
..2 Ratio of peduncle to combined peduncle and pedicel (0.20-) 0.35-0.41 (-0.70), foliaceous bracts appearing elevated on inflorescence; ratio of sepal length to sepal width (2.1-) 2.8-3.2 (-4.6); [east of the Mississippi River, from sc. TN southwards to SC, GA, FL, AL, and MS].
....3 Leaflets distinctly coriaceous with dense network of raised reticulate venation, average areole area small, (0.19-) 0.37-0.44 (-0.84) mm2; widest adaxial leaflet veins (not including mid-vein) (0.09-) 0.13-0.15 (-0.28) mm wide; leaflet apices usually rounded to broadly acute; sepal trichomes short with longest trichomes (0.27-) 0.32-0.39 (-0.47) mm long; achene rim (sum of both ends) to achene width ratio (0.22-) 0.26-0.32 (-0.38); [lower Coastal Plain of AL, FL, GA, MS, SC]
....3 Leaflets distinctly membranaceous to subcoriaceous, average areole area large (0.36-) 0.61-0.94 (-2.69) mm2, raised reticulate venation forming a sparsely concentrated network; widest adaxial leaflet veins (not including mid-vein) (0.04-) 0.07-0.09 (-0.14) mm wide; leaflet apices acute to acuminate, rarely rounded; sepal trichomes puberulent with longest trichomes (0.45-) 0.52-0.66 (-0.84) mm long; achene rim (sum of both ends) to achene width ratio (0.30-) 0.32-0.46 (-0.50); [n. and c. AL (mostly north of the Alabama River), wc. GA, ne. MS, and extreme sc. TN]
..2 Ratio of peduncle to combined peduncle and pedicel (0.02-) 0.07-0.10 (-0.20), foliaceous bracts appearing basal or near-basal on inflorescence; ratio of sepal length to sepal width (1.8-) 2.2-2.6 (-3.6); [either west of the Mississippi River or in c. and ec. TN].
......4 Leaflet undersurface usually densely puberulent (occasionally glabrous or sparsely puberulent); leaflets elliptic-oblong to rotund, occasionally ovate, with generally rounded apices; leaflets coriaceous; raised reticulate venation forming a densely concentrated network, the average closed areole area (0.19-) 0.33-0.46 (-1.22) mm2; widest adaxial leaflet veins (not including the midvein) (0.07-) 0.11-0.14 (-0.21) mm wide; [West Gulf Coastal Plain of sw. AR, w. LA, and e. TX]
......4 Leaflet undersurface glabrate to moderately pubescent; leaflets lanceolate to ovate, never rotund or elliptic-oblong, generally with distinctly acute or acuminate apices, rarely rounded; leaflets membranaceous to subcoriaceous; raised reticulate venation forming a sparsely concentrated network, average closed areole area (0.59-) 0.98-1.21 (-2.4) / mm2; widest adaxial leaflet veins (not including the midvein) (0.03-) 0.06-0.08 (-0.12) mm wide; [inland sedimentary rock provinces: Ouachita Mountains of sw. AR and se. OK, or Cumberland/Eastern Highland Rim/Central Basin of ec. TN].
........5 Primary pedicels long, (38-) 58.5-104.0 (-180.3) mm long, held erect above leaflets of corresponding node when in flower and fruit; longest sepal trichomes (0.25-) 0.28-0.40 (-0.47) mm long; sepal base color light vibrant pink to purple; achene length to width ratio 1.1-1.5 (1.9); achene tail hairs dark yellowish brown to coppery brown; [Cumberland/Eastern Highland Rim/Central Basin of ec. TN]
........5 Primary pedicels short, (16.2-) 13.5-38.0 (-69.19) mm long and pendulous, hanging below leaflets of corresponding node when in flower (erect in fruit); longest sepal trichomes 0.51-0.66 (-0.69) mm long; sepal base color dark purple to faded lilac; achene length to width ratio 1.0-1.2; achene tail hairs white to yellow; [Ouachita Mountains of sw. AR and se. OK]

Key B: Clematis flaccida complex

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1 Plants, glandular: peduncles, sepal exteriors, and lower leaf surfaces and leaf margins stipitate glandular; stems densely puberulent; [narrow endemic of the Nashville Basin of the Cumberland River Valley of TN]
1 Plants eglandular.
..2 Inflorescence long arcuate, the flowers arching above the stem; foliose bracts positio 1/4 to 1/2 of the peduncle length from the junction of the stem base; secondary and tertiary leaf veins never raised
..2 Inflorescence short-pendulous, the flowers hanging below the stem; foliose bracts positioned at the base of the peduncle; secondary and tertiary leaf veins raised.
....3 Lower leaf surface and sepal exteriors densely pubescent with villous and sericeous hairs; sepal exterior COLOR; pubescence entirely covering the epidermal tissue space between the raised secondand tertiary veins; [endemic to limestone escarpment barrens of the Cumberland Plateau of ne. AL, nw. GA, and TN]
....3 Lower leaf surface and sepal exteriors sparsely villous; sepal exterior magenta pink; pubescence absent between the secondary and tertiary veins; [endemic to prairie remnants of the Black Belt of AL]

Key C: Clematis viorna complex

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1 Plants decumbent along the ground as a subshrub only becoming scandent from axillary buds later in the growing season; flowers terminal and ebracteate; early spring flowering
1 Plants erect and vining; flowers solitary or cymose-paniculate within leaf axils; flowers always subtended by foliose bracts; flowering late spring to mid summer.
..2 Inflorescence long-arcuate; inflorescence of a solitary flower borne in the leaf axil; foliose bracts positioned 1/4 to 1/2 the way up the peduncle from its base; sepals bicolored, the sepal exterior red, the interior white; sepal apices short-reflexed, the sepal body broadly ovoid.
....3 Leaves thick, pseudo-reticulate, the leaf veins pronounced but not raised; peduncles and sepal exterior surfaces pubescent; sepal exterior magenta pink, the interior white; [acid substrates in lower Piedmont of GA, SC, and NC]
....3 Leaves thin, membranous, the leaf veins obscure; peduncles and sepals glabrous or puberulent; sepal exterior cherry red, the interior cream; [calcareous and mafic substrates, widespread in our region]
..2 Inflorescence short-pendulous; inflorescence cymose-paniculate (3-7-flowered); foliose bracts positioned at the base of the peduncle; sepals solidly colored, the sepal exterior dusky purple, the interior the same color; sepal apices long-reflexed, the sepal body cylindrical/conic.
......4 Leaves glaucescent; sepals glabrous; [shale bluffs of Coosa River tributaries]
......4 Leaves glabrous and green; sepas densely sericeous; [woodland edges of calcareous flatwoods and river bluffs of the Coosa, Flint, and Savannah River drainages]
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