1 Leaves mostly in whorls of 4 (rarely a few in whorls of 5-6 in some species) at the primary nodes

1 Leaves mostly in whorls of 6 or 8 at the primary nodes.

  2 Leaves mostly 6 per node (ranging from 5-8) at the primary nodes

  2 Leaves mostly 8 (or more) per node at the primary nodes; [clade III]

1 Largest leaves < 8 mm long; flowers white, yellow, or creamy; plant an annual, 0.5-3 dm tall; [clade VII].

  2 Inflorescences terminal and axillary, with pedicels > 5 mm long; [of w. AR, OK, and TX]

  2 Inflorescences axillary, the flowers on pedicels < 2 mm long; [collectively widespread].

    3 Flowers (1-) 2-3 in small clusters in leaf axils, the pedicels 1-2 mm long; fruits and ovaries glabrous

    3 Flowers solitary, sessile or subsessile in the leaf axils, the pedicels 0.3-0.8 mm long; fruits and ovaries pubescent with hooked hairs.

      4 Flowers about as long as the subtending bracts; stems hispidulous

      4 Flowers shorter than the subtending bracts; stems glabrous

1 Largest leaves > 8 mm long; flowers white, creamy, greenish-purple, maroon, or purple; plant a perennial, 1-8 dm tall.

        5 Larger leaves 2.5-25 mm wide, mostly 1.5-5 (-8)× as long as wide; fruits uncinate-hispid (except smooth in G. latifolium and G. arkansanum); flowers greenish, purplish, purple-and-cream, or yellow (in G. cruciata); leaves normally of very similar length and forming a symmetrical, neat whorl; [clade VII].

          6 Corollas yellow; flowers in axillary inflorescences; corolla tube very short

          6 Corollas greenish, purplish, purple-and-cream; flowers in terminal inflorescences; corolla tube longer.

             7 Leaves widest below the middle, tapering to a long-acuminate apex, averaging about 3-5 (-8)× as long as wide; largest leaves 30-80 mm long, 2.5-20 mm wide.

               8 Fruits uncinate-hispid; flowers yellowish, turning maroon

               8 Fruits smooth; flowers purple.

                 9 Leaves with 3-5 (-7) veins from the base, the lateral veins obvious; leaves 13-20 mm wide; [Appalachians]

                 9 Leaves with 1-3 veins from base, the lateral 2 veins obscure or absent; leaves 2.5-9 mm wide; [Interior Highlands]

                   10 Corollas glabrous on the exterior surface; leaves 5-9 mm wide, 1-3-veined

                   10 Corollas densely silky-pubescent on the exterior surface; leaves 2.5-3.5 mm wide and 1-veined

             7 Leaves widest at about the middle, tapering to an obtuse (or broadly acute) apex, averaging about 2-3× as long as wide; larger leaves 10-50 mm long, 5-25 mm wide.

                     11 Flowers (some of them) sessile or subsessile along the inflorescence branches; leaves 1.5-5 cm long, the larger usually > 2.5 cm long

                     11 Flowers all distinctly pedicelled; leaves 1-2.5 cm long

                       12 Stem glabrous; plants sprawling; leaves 2-5× as long as wide

                       12 Stem pubescent with either straight or upwardly incurved hairs; plants erect; leaves 1.5-2.5× as long as wide

        5 Larger leaves 1-6 mm wide, mostly 4-20× as long as wide (or 2-3.5× as long as wide in G. bermudense); fruits smooth or pubescent (if pubescent, the hairs not hooked at the end, though they may curve through their length, except uncinate in G. texense), either fleshy or dry; flowers white or creamy; leaves normally of differing lengths and also often forming asymmetrical, 'sloppy' whorls (the angles between the leaves not being 90°).

                          13 Fruits fleshy and blue-black; leaves firm, more-or-less evergreen, glandular-punctate beneath; [clade undetermined].

                            14 Leaves elliptic, 7-18 mm long, 3-6 mm wide, 2-3.5× as long as wide

                            14 Leaves linear, 15-25 mm long, 2-4 mm wide, 5-10× as long as wide

                          13 Fruits dry, and green, tan, or purplish; leaves herbaceous, deciduous, not glandular-punctate beneath.

                              15 Stems erect or nearly so; leaves 15-45 mm long, 2-6 mm wide; [clade VII]

                              15 Stems sprawling, matted (or erect in G. labradoricum); leaves 5-30 mm long, 0.5-5 (-6) mm wide; [clade V].

                                16 Stems smooth on the angles or with few, scattered hairs; stem nodes densely retrorsely bearded; corollas 4-lobed, the lobes longer than wide; leaves strictly 4 per node (very rarely 5 at a few nodes).

                                  17 Leaves strongly down-curved when fully grown; leaves 1-2.5 mm wide

                                  17 Leaves spreading; leaves (0.5-) 0.8-5 (-6) mm wide

                                    18 Leaves (8-) 10-20 (-25) mm long, (0.5-) 0.8-2 mm wide, margin usually smooth, with strongly down-rolled margins; corolla (1.8-) 2-2.5 (-3) mm across; pedicels filiform; stems 15-50 (-60) cm long, delicate

                                    18 Leaves (10-) 15-25 (-30) mm long, (2-) 3-5 (-6) mm wide, margin scabrous, not down-rolled; corolla (2-) 2.5-3.5 (-4) mm across; pedicels thicker; stems (15-) 25-60 (-80) cm long, firm

                                16 Stems retrorsely scabrous on the angles; stem nodes not conspicuously bearded; corollas 3-4-lobed, the lobes about as wide as long, or wider than long; leaves 4 per node, but most plants with at least some main stem nodes with 5 or 6 leaves.

                                       19 Flowers and fruits borne on arcuate pedicels, (5-) 7-15 (-20) mm long and densely retrorsely scabrous

                                       19 Flowers and fruits borne on straight pedicels, these (2-) 2.5-8 (-12) mm long and smooth.

                                         20 Fruiting pedicels (4-) 5-8 (-12) mm long; pairs of fruits (3-) 3.5-5 mm across at maturity; leaves 2-3 (-4) mm wide

                                         20 Fruiting pedicels (2-) 2.5-5 (-6) mm long; pairs of fruits 2-3 mm across at maturity; leaves (1.5-) 2-2.5 (-2.8) mm wide

1 Flowers pink, purple, or blue, in terminal heads, subtended by an involucre of leaves fused at the base; stem rough-hairy or retrorse-scabrid; [exotic].

  2 Leaves obtuse at tip; leaves 6-8 per whorl; stem retrorse-scabrid; [clade VI]

  2 Leaves acute to acuminate at tip; leaves (4-) 6 per whorl; stem rough-hairy; [clade IV]

1 Flowers white, yellow, or green, in axillary or terminal diffuse inflorescences, not subtended by an involucre; stems either smooth, retrorse-scabrid, or pubescent.

    3 Largest leaves < 10 mm long; fruits 0.7-1 mm across; annual; [exotic]; [clade III].

      4 Inflorescence relatively diffuse, branches divaricate; ultimate fruits (2-) 3-6 (-7) nodes beyond primary stem axis (with largest leaves); first inflorescence internode (beyond primary stem axis) 15-50 mm long; fruit surface glabrous (without hairs)

      4 Inflorescence relatively strict, branches ascending; ultimate fruits 2-3 (-4) nodes beyond primary stem axis (with largest leaves); first inflorescence internode (beyond primary stem axis) 3-12 (-20) mm long; fruit surface glabrous or bristly-hispid.

        5 Fruit surface without hairs, smooth to shallowly papillate

        5 Fruit surface bristly-hispid with uncinate-tipped hairs, distinctly papillate

    3 Largest leaves > 10 mm long; fruits 1-2.5 mm across; perennial; [native].

          6 Fruits and ovaries uncinate-hispid; leaves 15-50 mm long, 7-10 mm wide; [clade III]

          6 Fruits and ovaries glabrous or papillose; leaves 5-25 mm long, 1-6 mm wide.

             7 Corolla 1.5-2.5 mm across, 3-lobed; [collectively widespread in our area]; [clade V].

               8 Fruiting pedicels (4-) 5-8 (-12) mm long; pairs of fruits (3-) 3.5-5 mm across at maturity; leaves 2-3 (-4) mm wide

               8 Fruiting pedicels (2-) 2.5-5 (-6) mm long; pairs of fruits (2-) 2.5-3 mm across at maturity; leaves (1.5-) 2-2.5 (-2.8) mm wide

             7 Corolla 2.5-4.5 mm across, 4-lobed; [mostly of the Mountains in our area, extending into the Piedmont or even the Coastal Plain in n. VA and northward]; [clade undetermined].

                 9 Leaf margins retrorsely ciliate-scabrid; leaves 3-5× as long as wide; [plants of bogs and moist thickets]

                 9 Leaf margins antrorsely ciliate-scabrid; leaves 4-8× as long as wide; [plants of dry forests and woodlands].

                   10 Leaves sharply acute or cuspidate; corolla 2.5-3 mm across

                   10 Leaves rounded, obtuse, or barely acute; corolla ca. 4 mm across

1 Leaves 8-12 per whorl (many whorls with > 8 leaves); flowers bright yellow, in a large showy terminal compound inflorescence; fruits glabrous; perennial.

  2 Flowers golden-yellow, fragrant; inflorescence dense, usually not interrupted

  2 Flowers lemon-yellow, odorless; inflorescence interrupted

1 Leaves (5-) 8 (-10) per whorl (few if any whorls with > 8 leaves); flowers white or greenish, in a terminal compound inflorescence or in small axillary inflorescences; fruits glabrous, papillose, or uncinate-hispid; annual or perennial.

    3 Stems retrorsely scabrous; annual.

      4 Fruits and ovaries sharply papillose; flowers and fruits mainly in clusters of 3

      4 Fruits and ovaries smooth or with hooked bristles; flowers and fruits mainly in clusters of 2-5.

        5 Flowers white, 2-3.5 mm in diameter; pollen grains 25-30 microns (μ) in polar diameter; fruits usually 2.8-4 mm long (excluding the bristles when present) but occasionally smaller; fruits with bristles (very rarely smooth), the bristles with bulbous bases; stem nodes usually tomentose but sometimes almost glabrous; leaves linear-oblanceolate, lax, to 50 mm long and 5 mm wide

        5 Flowers greenish-yellow, 0.8-1.5 mm in diameter; pollen grains to 24 microns (μ) in polar diameter; fruits 1.5-2.8 mm long (excluding the bristles, when present); fruits smooth or with bristles, the bristles wider at the base but not bulbous; stem nodes glabrous or lightly pubescent; leaves narrow, linear-lanceolate, mucronate, firm textured, to 40 mm long and 3 mm wide

    3 Stems glabrous or pubescent, but not scabrous; perennial.

          6 Fruits and ovaries uncinate-hispid; nodes bearded, the stem otherwise glabrous; [section Hylaea]

          6 Fruits and ovaries glabrous; nodes not bearded, the stem either glabrous or pubescent toward the base of the plant.

             7 Corolla 3-5 mm across, the pedicels usually shorter than the width of the corolla; inflorescence branches ascending, mostly at < 45 degrees

             7 Corolla 2-3 mm across, the pedicels usually longer than the width of the corolla; inflorescence branches spreading, mostly at > 45 degrees