No key was found for the requested taxon, but its parent (Ruellia) is keyed as shown below.

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Key to Acanthaceae

Acanthaceae

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1 Plant a tree, with opposite leathery leaves; [of FL, s. MS, s. LA southward]
1 Plant an herb or vine, with various leaf arrangements.
  2 Leaves in a basal rosette (sometimes with smaller leaves on a scape).
    3 Leaves glabrate, to 22 cm long and 8 cm wide; corolla 0.8-1.3 cm long; capsule 8-10 mm long; stamens 2; [of moist to wet swamps]; [subfamily Nelsonioideae]
    3 Leaves pubescent, to 10 cm long and 3 cm wide; corolla 1.8-4 cm long; capsule 9-18 mm long; stamens 4; [of dry upland pinelands].
      4 Leaves 2-10 cm long, 1-3 cm wide; corolla 3-4 cm long; calyx lobes 15-30 mm long; capsule 12-18 mm long
      4 Leaves 1.5-2.5 cm long, 0.7-0.8 cm wide; corolla ca. 2 cm long; calyx lobes 6-9 mm long; capsule ca. 10 mm long
  2 Leaves cauline.
        5 Fertile stamens 2; corolla distinctly 2-lipped or zygomorphic (except salverform in Pseuderanthemum and with 4 nearly equal lobes in Yeatesia).
          6 Corolla distinctly 2-lipped or 4-lobed.
             7 Leaves speckled or mottled with pink or white
             7 Leaves not speckled with pink or white.
               8 Flowers with 2 staminodes present; corolla tubular; anther sacs parallel, equal; [uncommon non-native, s. AL and FL]
               8 Flowers lacking staminodes; corolla not tubular; anther sacs unequal; [widespread native and non-natives]
                 9 Texas only; {additional characters}
                   10 Stout shrubs to 3 m tall; corolla bright red to orange, 30-55 mm long
                   10 Suffrutescent herbs to 0.5 m tall; corolla white to light purple, 5.0-9.5 mm long
                 9 yyyy; [widespread, including TX].
                     11 Bracts and bractlets inconspicuous, 2-5 mm long, linear or triangular; stem subterete or obscurely 4-angled
                     11 Bracts and/or bractlets subtending the flowers conspicuous, 5-15 mm long, obovate; stem terete or 6-angled.
                       12 Stem six-angled in cross-section; corolla conspicuously 2-lipped
        5 Fertile stamens 4; corolla not distinctly 2-lipped, the corolla lobes of nearly equal size (except distinctly 2-lipped in Hygrophila).
                          13 Corolla distinctly 2-lipped (bilabitate, with a distinct upper and lower lip).
                            14 Outer sepals aristulate or with spinose margins (except B. repens, which has a reddish corolla and grows trailing)
                          13 Corolla not distinctly 2-lipped, the corolla lobes of nearly equal size.
                              15 Plant an herbaceous vine; leaves cordate-hastate at the base; flowers yellow to orange, usually with a dark purple “eye”
                              15 Plant an herb; leaves cuneate to rounded at the base; flowers white to various shades of blue or pink.