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Key to Houstonia

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1 Flowers solitary, on terminal or axillary pedicels 0-50 (-70) mm long; corolla salverform; leaves 2-15 (-20) mm long.
  2 Stems prostrate and creeping, rooting at the nodes.
    3 Corolla white (rarely pale lavender); capsule (2.3-) 3.0-6.3 mm across; leaves 2-13 mm wide; pedicels usually single, 2-25 mm long; flowers chasmogamous and cleistogamous (the cleistogamous borne underground); [of the outer Coastal Plain]
    3 Corolla blue (rarely white); capsule 2.5-5.0 mm across; leaves 0.5-7 mm wide; pedicels single or paired, to 60 mm long; flowers all chasmogamous and aerial; [of the Mountains]
  2 Stems erect or spreading to prostrate, not rooting at nodes (even if prostrate).
      4 Flowers borne in leaf axils; pedicels either straight or recurving in fruit; annuals with a long, thin, sparingly branched taproot; [TX, AR, OK westwards and southwards].
        5 Corollas 5-8 mm long; stipules to 2.5 mm long, bearing bristles at the margin; flowers heterostylous
        5 Corollas 1-3 mm long; stipules < 0.5 mm long, lacking marginal bristles; flowers homostylous.
          6 Corollas 1-2 mm long, about as long as the calyx; capsules erect, glabrous
          6 Corollas 2-3 mm long, longer than the calyx; capsules recurved, short-hairy (hirtellous).
             7 Cauline leaves (the larger) > 1 mm wide; pedicels 0-2 mm long; capsules 1/4 to 1/2 inferior
             7 Cauline leaves < 1 mm wide; pedicels 3-8 mm long; capsules about 3/4s inferior
      4 Flowers borne terminally on the stem; pedicels remaining straight in fruit, thus the capsules borne upright; annuals or perennials with fibrous and branched roots; [collectively widespread in our region].
               8 Stems 1-4 (-7) cm tall; leaves mostly oblanceolate, 0.3-3.0 mm wide; corolla 5-12 mm long, white to pale pink; seeds with a hilar ridge in an elliptical depression
               8 Stems 1-26 cm tall; leaves elliptic, ovate or spatulate, 0.3-9.0 mm wide (at least some on a plant generally > 3 mm wide); corolla 2-21 mm long, purple, pale blue, pink, or white; seeds subglobose with a ventral cavity.
                 9 Plants perennial, with a well-developed, persistent basal rosette; corolla 5.8-16 (-21) mm long, the tube (2-) 4-11 (-12) mm long
                 9 Plants annual, with at most a few short-lived basal leaves; corolla 2-10 (-12) mm long, the tube 0.8-5.5 mm long.
                   10 Calyx lobes slightly shorter than to slightly longer than the corolla tube; corollas white, 2.0-5.5 mm long, the tube 0.8-2.5 mm long
                   10 Calyx lobes 1/5 as long as to slightly longer than the corolla tube; corollas purple or violet (rarely white), 3.5-10 (-12.5) mm long, the tube 2.0-5.5 mm long
1 Flowers several to many, in terminal cymes; corolla funnelform; leaves (8-) 10-60 mm long.
                     11 Stipules of mid-cauline leaves ciliate or fringed, and also often bristle-tipped; largest mid-cauline leaves 0.5-3 mm wide; capsule either obovoid-cylindric, longer than wide, the free calyx lobes distinctly shorter than the capsule, or (in var. floridana) globose or subglobose; [of calcareous glades and barrens or in FL of calcareous sands]
                       12 Capsule globose or subglobose, 1-1.3× as long as wide; largest leaves 0.3-1.2 mm wide; [of pine rocklands in s. FL]
                       12 Capsule turbinate, oblong, or ellipsoid, 1.3-2.2× as long as wide; largest leaves 0.5-6 mm wide; [widespread in our area, and in various habitats]
                          13 Largest mid-cauline leaves 3-6 mm wide; main stem leaves lacking axillary shoot leaf fascicles; inflorescence loose, usually with 5-10 pure white flowers per square cm in pressed specimens; corolla pure white; [of limestone palisade cliffs of KY and TN]
                          13 Largest mid-cauline leaves 0.5-3 mm wide; main stem leaves with axillary shoot leaf fascicles; inflorescence loose, usually with 10-20 flowers per square cm in pressed specimens; corolla pale blue; [collectively widespread in our area]
                            14 Calyx, upper stems, and leaves glabrous or ciliate along margins; [collectively widespread, including s. TX].
                              15 Stem internodes 2-10 (-20) mm long; plants branched at and near the base, the branches sprawling or decumbent, mat-forming; [of FL dunes and beaches]
                              15 Stem internodes 6-46 mm long; plants branched less prolifically, if branched at or near the base, the branches ascending or vertical; [widespread in our area, usually on rocky, calcareous substrates]
                     11 Capsule as long as wide or wider, depressed globose, the free calyx lobes about as long as the capsule; stipules of mid-cauline leaves not ciliate, fringed, or bristle-tipped; leaves 0.5-34 mm wide; [of various habitats, including calcareous glades and barrens]
                                16 Basal leaves absent at the onset of flowering; leaves smooth-margined or ciliate.
                                  17 Leaves ovate or lanceolate, 1-6× as long as wide, 4-34 mm wide, widest toward the base or at the middle; calyx lobes 1-7 mm long.
                                    18 Calyx lobes 4-7 mm long; leaves mostly lanceolate (varying from narrowly lanceolate to broadly ovate), 17-33 mm long, 4-10 mm wide, 3.3-6× as long as wide
                                    18 Calyx lobes 1-4 mm long; leaves mostly ovate (varying from broadly ovate to ovate-lanceolate), 8-63 mm long, 6-34 mm wide, 1-3.2× as long as wide.
                                       19 Corollas light purple to white, (4-) 5-8 (-10) mm long; leaves (10-) 25-50 (-60) mm long, (6-) 12-30 (-34) mm wide; stems sparsely to densely pubescent; median internodes 2-9 cm long; leaves with pubescence ciliate on the leaf margin, on the midrib, and scattered on the surface; [of various habitats, widely distributed]
                                       19 Corollas deep purple, 8-12 mm long; leaves 8-20 (-30) mm long, 3-8 (-13) mm wide; stems glabrous (or slightly short-pubescent on the lower nodes only); median internodes 0.5-4 cm long; leaves entirely glabrous or with pubescence ciliate on the leaf margin, on the midrib, but lacking from the leaf surface; [of high elevation rocky summits and adjacent grassy balds in w. NC, e. TN, and sw. VA]
                                  17 Leaves linear to narrowly elliptic, 4-20× as long as wide, 0.5-6 mm wide, widest at the middle or near the apex or nearly equally wide for most of their lengths; calyx lobes 0.5-3 mm long.
                                         20 Corolla lobes densely pilose within, the hairs 0.5-1.2 (-1.8) mm long; cauline leaves 0.3-2.0 (-3.5) mm wide; stems glabrous; [of AR and OK]
                                         20 Corolla lobes glabrous within, or, if pubescent, with hairs < 0.5 mm long; cauline leaves 0.5-8.0 mm wide; stems glabrous or puberulent; [widespread in our area].
                                           21 Leaves 1.3-4.7 cm long, 0.5-4.0 mm wide (mostly < 2.5 mm wide), 7-20× as long as wide; inflorescence very diffuse and open, to 20 cm long, the branches ascending, spreading, or deflexed, slender and often ultimately filiform, with 1-4 remote nodes bearing reduced leaves, the pedicels to 14 mm long; internodes mostly 4-9; mature capsules mostly 1.5-2.5 mm long and wide; stem densely cinereous-puberulent, especially at the nodes
                                           21 Leaves 1.6-4.0 cm long, 1.5-6.0 mm wide (mostly > 2.5 mm wide), 4-11× as long as wide; inflorescence rather open to rather compact, < 12 cm long, the branches ascending or spreading, slender, pedicels to 8 mm long; internodes mostly 7-11; mature capsules mostly 1.8-3.0 mm long and wide; stem densely cinereous-puberulent, glabrate, or glabrous.
                                             22 Internodes 4-7; stipules of median nodes ovate, to 3.3 mm long, to 3.5 mm wide, the apex often rounded; [northern, reaching our area in n. NJ]
                                             22 Internodes (6-) 7-11 (-13); stipules of median nodes lanceolate or deltoid, to 3 mm long, to 2.5 mm wide, the apex usually acute to acuminate; [collectively widespread].
                                               23 Stems glabrous or glabrate (sometimes puberulent on the nodes only); internodes 7-10, the median internodes (1.1-) 2.0-4.5 (-6.0) cm long; [of seasonally wet soil mats on moderate to high elevation granitic domes in sw. NC, nw. SC, and ne. GA]
                                               23 Stems densely cinereous-puberulent; internodes (6-) 7-11 (-13), the median internodes (1.0-) 1.5-3.5 (-4.4) cm long; [of dry sandy, shaley, gravelly, or rocky soil, widely distributed]
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