1 Stem herbaceous, lacking prickles; ovules 2 per carpel; peduncles usually > 4 cm long; petioles 1-10 cm long; [section Nemexia]; [Clade C1].

  2 Plants erect, 0.2-1.0 m tall, even when well-developed with < 20 leaves [note that immature or depauperate individuals (nonflowering) of S. pseudochina, S. herbacea, S. lasioneura, and S. pulverulenta often have this aspect]; tendrils absent or rudimentary; peduncles usually few (usually 1-4), the lowest often from bract axils.

    3 Leaves glabrous and glaucous beneath, thick in texture, base cordate, tip acute or acuminate; lowest inflorescence from a leaf axil (very rarely from bract axils), upper inflorescences from leaf axils; leaves 4-7, clustered together near the summit of the stem

    3 Leaves pubescent and green (or glaucous) beneath, usually thin in texture, base cordate, truncate, or rounded, tip acuminate, acute, or obtuse; lowest inflorescence(s) from axils of bracts below the lowest leaves, upper inflorescences also often from bracts (the uppermost often from leaf axils); leaves 4-25, either clustered together near the summit of the stem or well distributed.

      4 Leaves few, usually 4-8, usually clustered together near the summit of the stem (rarely well distributed), about the same size, mostly with the base ovate (to subcordate), the tip acute to obtuse; berry 2-3 seeded

      4 Leaves relatively many, (4-) 6-13 (-20), often well distributed in the upper half of the stem, notably reduced in size from lower to upper, mostly with the base cordate and the tip acuminate; berry 3-5 seeded.

        5 Leaves of the lower stem broadly ovate, the base cordate; petioles equal in length or shorter than the length of the blade

  2 Plants vine-like, climbing or sprawling, to 3 m tall, when well-developed with > 30 leaves [note that immature, nonflowering individuals may be much shorter and have fewer leaves]; tendrils present and numerous; peduncles usually many, from leaf axils.

          6 Leaf bases hastate, the leaf margins straight or concave in outline; longest fruiting pedicels < 2× as long as the fruit; anthers equaling or longer than the filaments; perianth 1.5-2.5 mm long; leaves glabrous and glaucous beneath

          6 Leaf bases cordate, the leaf margins convex in outline; longest fruiting pedicels 2× or more as long as the fruit; anthers shorter than the filaments; perianth 3.5-6 mm long; leaves either puberulent beneath (at least along the veins), or glabrous and glaucous beneath.

             7 Leaves glabrous and glaucous on the lower surface; fruit dark blue and glaucous.

               8 Peduncles 5-8× as long as the subtending petioles; principal veins of the leaf nearly evenly spaced.

               8 Peduncles 2-3× as long as the subtending petioles; principal veins of the leaf unevenly spaced, the middle 3 much closer to one another than the outer veins.

             7 Leaves puberulent on the lower surface, at least on the veins; fruit dark blue and glaucous or black and not glaucous; peduncles 1-10× as long as the subtending petioles.

                 9 Leaves pale green and dull below; fruit dark blue, glaucous; peduncles (3-) 5-10× as long as the subtending petioles

                 9 Leaves bright green and shiny beneath; fruit black, not glaucous; peduncles 1-2 (-3)× as long as the subtending petioles

1 Stem woody, usually with prickles; ovules 1 per carpel; peduncles usually < 3 cm long; petioles 0.1-2 cm long; [section China].

                   10 Stems and petioles tomentose, lacking prickles; leaves densely tomentose beneath; berries orangish-red, obpyriform, with an acutish beak; plant trailing or ascending, the stem rarely > 0.5 m long (with determinate growth); [Clade B4]

                   10 Stems and petioles stellate-scurfy or glabrous, generally with prickles; leaves glabrous or papillate beneath; berries black, dark blue, dark red, or bright red, globose, subglobose, or ovoid, lacking a beak; plant climbing, ascending, or trailing, mature plants with stems generally well over 0.5 m long (with indeterminate growth).

                     11 Lower surfaces of leaves strongly white-glaucous; [Clade B5]

                     11 Lower surfaces of leaves green (rarely very slightly glaucous).

                       12 Prickles of the larger stems abundant, thin and needle-like, shiny brown or black, colored fully (not “dipped” just at the tips) (smaller and upper stems often with few or no prickles); leaf margins often with minute, flattish, tooth-like projections (= enations, visible under 10× magnification); petioles 7-34 mm long; leaves with 5-7 primary veins, which are noticeably impressed into the upper leaf surface; [Clade B2].

                          13 Leaves with basal lobes, pandurate to occasionally hastate; petioles 0.7-2.9 mm long; [Coastal Plain]

                          13 Leaves with no lobes, oblong to ovate; petioles 0.7-3.4 mm long; [widespread]

                       12 Prickles of the larger stems fewer, broad-based and awl-like or catclaw-like, green, brown, or black on the tips (“dipped”); leaf margins either fully entire, or spinose as in S. bona-nox and S. havenensis (occasional marginal enations present on S. rotundifolia); petioles 5-22 mm long; leaves with 3-7 primary veins, which are not noticeably impressed into the upper leaf surface.

                            14 Margin of the leaf blade with a prominent marginal cartilaginous band (this appearing as a thickening, a visible vein, or an apparent revolute margin); berries with 1-3 seeds.

                              15 Inflorescence peduncle (stalk of the umbel) 11-65 mm long, > (1.5-) 2× as long as the subtending leaf petiole; stems (especially the lower) and prickles either brownish stellate-scurfy or glabrous; leaves semi-evergreen to evergreen and thin; peduncles 15-60+ mm long; berries with 1 seed; [Clade B5].

                                16 Tubers and rhizomes with abundant tiny rounded bumps, plus densely covered with many sharp to blunt spines < 1 cm long and with dark, shiny tips; tubers lacking thorns; lower portion of aerial stems covered with abundant tiny raised bumps, each with compound stellate hairs distally; leaves with 5-7 primary veins; [various habitats, including wetlands]

                                16 Tubers and rhizomes with abundant tiny rounded bumps, with no spines or few and poorly developed sharp to blunt spines; tubers bearing simple or branched, woody, narrowly conical thorns; lower portion of aerial stems smooth, stellate hairs absent; leaves with 7-11 primary veins; [dry to moist maritime habitats]

                              15 Inflorescence peduncle (stalk of the umbel) 1-17 mm long, about as long as or shorter than the subtending leaf petiole; stems and prickles glabrous; leaves evergreen and thick; peduncles 2-16 mm long; berries with (1-) 2-3 seeds.

                                  17 Most leaf margins and mid-veins with scattered spines; [s. FL rocklands]; [Clade B3]

                                  17 Leaf margins entire; [widespread in the southern portions of our region, especially Coastal Plain].

                                    18 Leaf blades 4.5-6 (-8.5) cm long, 1.4-5.8 cm wide; prickles 1-4 mm long; secondary leaf veins prominently raised on lower surface; leaf blades various in shape, frequently broadened or auricled below the midpoint; [dry to moist habitats, e. NC south to s. FL, west to e. LA, Coastal Plain]; [Clade B5]

                                    18 Leaf blades (5.2)7-13 cm long, 1.3-4 (-6) cm wide; prickles 6-12 mm long; secondary leaf veins not prominently raised on lower surface; leaf blades evenly oblong throughout (“laurel-like”); [pocosins, bogs, swamps, and other habitats, usually with saturated hydrology, NJ to s. FL, west to e. TX and se. OK, mainly Coastal Plain but also inland]; [Clade B4]

                            14 Margin of the leaf blade thin, sometimes slightly revolute; berries with (1-) 2-4 seeds.

                                       19 Margins of the leaves and the petioles often with minute, flattish, tooth-like projections; leaf blades 4.2-16 cm wide; leaf blades broadly ovate (< 1.5× as long as wide); berries blue-black to black; pedicel bases lacking prominent bracts; [a wide variety of upland and wetland habitats]; [Clade B5]

                                       19 Margins of the leaves and the petioles lacking minute, flattish, toothlike projections; leaf blades 1.5-4.8 cm wide; leaves lanceolate to ovate (> 1.5× as long as wide); berries black, or dull to bright red; pedicel bases with prominent ruffled bracts.

                                         20 Leaves evergreen, mid-vein and petiole green; berries black to dull red; perianth green; [a wide variety of upland and wetland habitats]; [Clade B4]

                                         20 Leaves deciduous, often with a red mid-vein and petiole; berries bright red; perianth brownish-yellow; [swamp forests, bogs, often where submersed for at least part of the year]; [Clade B5]