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Key to Geocarpon

Caryophyllaceae

Geocarpon

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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 oblinear 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, the 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 (thus populations often consisting of many single stemmed individuals); 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 (thus populations often consisting of multi-stemmed clumps); cymes mostly 3-7-flowered; sepals 3.5-5.5 mm long; petals 6-10 mm long; [of mountain peaks and Piedmont monadnocks]