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Key to Ruellia

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1 Plant a shrub; [section Blechum]
1 Plant an herb.
  2 Inflorescence a bracteate, 4-sided spike, either terminal or axillary; [section Blechum]
  2 Inflorescence not prominently bracteate and 4-sided, either of terminal cymose panicles, or axillary and either solitary or of clusters
    3 Flowers borne in terminal cymose panicles (the flower not directly subtended by a leaf); [section Ruellia].
      4 Leaf base truncate or rounded; midvein and main secondary veins impressed into the leaf surface from above; inflorescence raceme-like, much longer than broad; [exotic]
      4 Leaf base broadly cuneate; midvein and main secondary veins not impressed into the surface from above; inflorescence panicle-like or corymb-like, diffuse because of elongate peduncles and repeated branching of cymose units; [native, of AL westwards].
        5 Corolla (50-) 55-65 mm long, white (to pale bluish purple), very slightly curved; calyx 14-20 mm long in flower
        5 Corolla 35-50 (-55) mm long, lavender to bluish purple, strongly curved; calyx lobes 10-15 mm long in flower.
          6 Corollas 40-50 (-55) mm long; capsule pubescent entirely or mostly eglandular; [Coastal Plain from AL westwards to TX]
          6 Corollas < 40 mm long; capsule pubescent entirely or mostly glandular; [mainly Tamaulipan Plain of s. TX]
    3 Flowers borne in leaf axils (including at upper and terminal nodes), solitary or in either sessile or pedunculate clusters.
             7 Principal leaf blades linear-lanceolate, > 10× as long as wide (8-27 cm long, 0.7-2 cm wide); [exotic, cultivated and naturalized]; [section Ruellia]
             7 Principal leaf blades elliptic, ovate or broadly lanceolate, 2-5 × as long as wide (2-16 cm long, 0.5-7 cm broad); [native or exotic].
               8 Plant with a rosette of basal leaves, flat on the ground, and 0 (-2) pairs of leaves on the stem; [restricted to dry pinelands in the Coastal Plain]; [section Boreosilva]
               8 Plant with all leaves on the stem; leaves ovate, lanceolate, elliptic, or oblong; [collectively widespread in our area].
                 9 Calyx lobes narrowly linear-lanceolate, flattened to the tip, 1-4 mm wide; larger leaf blades 7-18 cm long, 3-9 cm wide; [section Boreosilva]
                 9 Calyx lobes linear, filiform or setaceous at least apically, < 1.2 mm wide at their widest point (usually the base), hairlike at the tip; larger leaf blades 2-11 cm long, 0.8-5 cm wide.
                   10 Flowers borne on peduncles 0.2-7 cm long, from the axils of lower and median nodes, not from the terminal node or terminal cluster; capsules glabrous (R. pinetorum) or variously hairy (R. purshiana, R. pedunculata); [section Boreosilva].
                     11 Stem simple (rarely with a few ascending branches); calyx pubescent, without cystoliths; calyx lobes 0.7-1.2 mm wide, widest near the middle and tapering to the apex; capsules puberulent; [of dry woodlands, forests, and glades of the Piedmont and Mountains]
                     11 Stem divergently branched (rarely simple); calyx lobes 0.5-1 mm wide, tapering from the base to a very slender tip; capsules glabrous or puberulent.
                       12 Ovaries and capsules puberulent with short-spreading hairs; calyx puberulent; [of dry slopes, barrens, and woodlands of s. IL and MO south through w. KY, AR, and e. OK to e. and w. LA and e. TX]
                       12 Ovaries and capsules glabrous; calyx glabrous or glabrate, with many partially imbedded cystoliths; [of dry to wet pine woodlands of the Coastal Plain]
                   10 Flowers sessile or subsessile, in the axils of median and upper nodes, and usually also from the terminal node or cluster; capsules glabrous (or at most with a few scattered hairs).
                          13 Corolla 6-10 cm long, opening at night and withering by mid-morning, white to pale lavender; calyx lobes 2.5-4.5 cm long; [of Coastal Plain seepage bogs and wet pine flatwoods]; [section Boreosilva]
                          13 Corolla 3-7 cm long, opening during the day, lavender to lavender-blue (rarely white in R. humilis); calyx lobes 1-2.5 (-3) cm long; [of various habitats].
                            14 Leaf blades averaging about 4× as long as wide; leaf petioles (5-) 8-20 mm long; [exotic]; [section Blechum]
                            14 Leaf blades averaging 2-3× as long as wide; leaf petiole 0-10 mm long; [native]; [section Boreosilva].
                              15 Leaves sessile or subsessile; flower-bearing nodes usually 4-8; stem typically branched at base
                              15 Leaves short-petioled; flower-bearing nodes usually 1-3; stem typically simple below (unless damaged), sometimes branched upward
                                16 Plant glabrous or nearly so, upright, to 30 cm tall; leaves thick, somewhat fleshy, often purple-tinged
                                16 Plant variously pubescent, upright or with long-spreading lower stems, to 80 cm tall; leaves thin, green.
                                  17 Stems upright (to 80 cm tall), either simple or with short lateral branches, sparingly pubescent; [widespread in our area]
                                  17 Stems in early season upright (to 40 cm tall), in mid to late season forming long trailing horizontal branches from lower nodes, hirsute to villous; [dry-mesic pinelands, marl prairies, pine rocklands, of s. peninsular FL]