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| 1 Flowers sessile, axillary; plants to 4 cm tall; petals absent; sepals fused into a cuplike hypanthium |
| 1 Flowers either (1-) 5-50+ in terminal corymbose cymes, or if solitary and axillary on pedicels 10-40 mm long; petals present or (in Sabulina fontinalis) absent; sepals separate. |
| ..2 Flowers solitary in leaf axils; petals absent; [calcareous seepage, KY, TN, n. AL] |
| ..2 Flowers (1-) 5-50+ in terminal corymbose cymes; petals present. |
| ....3 Sepals acute to acuminate at the tip; sepal venation prominently 3- or 5-veined, or (in Geocarpon nuttallii) obscure. |
| ......4 Plants perennial from woody crowns; leaves rigid, with axillary fascicles; pedicels glabrous |
| ......4 Plants either annual or perennial from slender wintering stems; leaves flexuous, lacking axillary fascicles; pedicels sparsely to densely stipitate-glandular. |
| ........5 Stems prostrate or decumbent, leafy throughout; [of moist habitats] |
| ........5 Stems erect, leafy mostly near the base, the stem leaves few in number and reduced in size upward; [of moist to dry upland habitats]. |
| ..........6 Sepals 3-nerved; leaves narrowly lanceolate to narrowly oblanceolate, (0.6-) 1.5-3.2 mm wide; seeds 0.7-0.9 mm long, the surface appearing pebbled or with short papillae, black |
| ..........6 Sepals 5-nerved or 5-ribbed; leaves narrowly olinear to linear, 0.5-1.5 (-1.8) mm wide; seeds 0.5-0.7 mm long, the surface tuberculate, reddish brown to black |
| ....3 Sepals obtuse or rounded at the tip; sepal venation obscure. |
| ............ 7 Leaves rigid, closely imbricated, with axillary fascicles of leaves; pedicels densely stipitate-glandular; plants perennial from a very long and deep, woody taproot; [xeric sands; Coastal Plain NY to FL Panhandle] |
| ............ 7 Leaves flexuous, not imbricated, lacking axillary fascicles of leaves; pedicels either glabrous or (in Geocarpon nuttallii) stipitate-glandular; plants either annual or perennial from a basal mat of offshoots, taproots filiform; [thin soils over rock outcrops; inland provinces]. |
| ............ ..8 Pedicels stipitate-glandular; [west of the Mississippi River in AR, LA, OK, and TX] |
| ............ ..8 Pedicels glabrous; [east of the Mississippi River]. |
| ............ ....9 Leaves oblanceolate, 1-3 mm wide, very thin in texture and prominently though minutely veined; flowers in cymes of mostly 1-3 flowers; [shaded Cumberland Plateau rockhouses of s. KY and n. TN] |
| ............ ....9 Leaves linear, mostly < 1 mm wide, thicker in texture, then veins not readily apparent; flowers in cymes of mostly 3-25+ flowers; [collectively of sunny thin-soil-over-rock habitats of the Piedmont and Appalachians]. |
............ ......10 Seeds 0.4-0.6 mm long, suborbicular, lacking an adaxial groove; petals oblanceolate, not clawed |
| ............ ......10 Seeds 0.5-0.8 mm long, obliquely triangular, with an adaxial groove; petals clawed, broadly obovate. |
| ............ ........11 Plants annual, 10-20 cm tall; cymes mostly 9-15-flowered; sepals 3-4 mm long; petals 4-6 (-8) mm long; [of Piedmont and low mountain granitic flatrocks and other outcrops] |
| ............ ........11 Plants perennial from a basal mat of offshoots, 5-10 (-15) cm tall; cymes mostly 3-7-flowered; sepals 3.5-5.5 mm long; petals 6-10 mm long; [of mountain peaks and Piedmont monadnocks] |