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See list of 19 species in this genus

Reference: Pennell (1921).

  • 1a. Racemes borne in the axils of leaves [Figs. 776,777]; individual flowers subtended by very small, narrow bracts that are much smaller than the foliage leaves [Figs. 776,777]; leaves opposite throughout; plants perennial
    • 2a. Stems and usually the leaf blades conspicuously pubescent; styles 2.5–8 mm long; plants of mesic to dry-mesic habitats
      • 3a. Flowering stems creeping near the base, the tip ascending; leaf blades thick, subcoriaceous, permanently pubescent; corolla 4–8 mm wide; capsules distinctly exceeding the calyx
      • 3b. Flowering stems ascending to erect; leaf blades thin, membranaceous, becoming glabrate; corolla 8–13 mm wide; capsules not, or only slightly, exceeding the calyx
        • 4a. Leaf blades ovate, 1–2 times as long as wide; style 3–5 mm long; sepals subequal in length; stems 10–40 cm tall
        • 4b. Leaf blades lanceolate to ovate, 2–4 times as long as wide; style 6–8 mm long; upper sepals much shorter than the lower sepals; stems 30–80 cm tall
    • 2b. Stems and leaf blades essentially glabrous; styles 1.5–4 mm long; plants of hydric habitats
      • 5a. Leaf blades linear to lanceolate, mostly 4–20 times as long as wide; rachis of raceme flexuous; seeds 1.2–1.8 mm long
      • 5b. Leaf blades lanceolate or narrow-oblong to narrow-ovate or oblong-obovate, 1.5–5 (–8) times as long as wide; rachis of raceme straight; seeds up to 0.5 mm long
        • 6a. Leaf blades borne on short, but evident, petioles [Fig. 776]; racemes with (4–) 10–25 (–30) flowers
          • 7a. Leaf blades lanceolate to narrow-ovate or subtriangular (the lower leaf 
blades often more elliptic), broadest near the base, acute to subacute at the apex [Fig. 776]; style 2.5–3.5 mm long
          • 7b. Leaf blades oval or oblong to oblong-obovate, broadest near or distal to the middle, rounded at the apex; style 1.8–2.2 mm long
        • 6b. Leaf blades of the flowering stems sessile [Fig. 777]; racemes with (15–) 20–54 (–60) flowers
          • 8a. Leaf blades elliptic to elliptic-ovate, 1.5–3 times as long as wide [Fig. 777]; sepals acute to acuminate; corolla 5–8 mm wide; mature pedicels ascending or upcurved; capsules nearly or fully as wide as tall, scarcely notched at the apex; sterile autumnal shoots formed, with rounder and short-petiolate leaves
          • 8b. Leaf blades lanceolate to narrow-oblong, (2.5–) 3–5 (–8) times as long as wide; sepals obtuse to subacute; corolla 3–5 mm wide; mature pedicels wide spreading; capsules wider than tall, usually with a conspicuous apical notch; sterile autumnal shoots not formed
  • 1b. Racemes terminating the main stem [Figs. 778,779]; flowers subtended by foliaceous bracts or by very small, narrow bracts in V. longifolia and V. spuria [Fig. 778]; upper leaves 
(i.e., the foliaceous ones that subtend flowers) alternate in most species [Fig. 778]; plants annual or perennial
    • 9a. Plants perennial, from rhizomes, sometimes also rooting at the lower nodes of the stem
      • 10a. Leaf blades 30–100 mm long, the principal ones sharply and conspicuously serrate, often some whorled on a given plant; style 4–10 mm long, ca. 2 times as long as the capsule; capsules pubescent with eglandular hairs; stems 3–15 dm tall
        • 11a. Racemes several to many, arranged in a panicle; corolla 7–14 mm in diameter; stamens not exserted beyond corolla; pedicels (2–) 3–5 mm long, approximately as long as the calyx
        • 11b. Racemes solitary or a few together, not arranged in a panicle; corolla 6–8 mm 
in diameter; stamens exserted beyond corolla; pedicels 1–2 mm long, shorter than 
the calyx
      • 10b. Leaf blades 5–40 mm long, entire or with inconspicuous and/or blunt teeth, none whorled [Fig. 779]; style 1–3.5 mm long, shorter than to about as long as the capsule; capsules pubescent, at least in part, with glandular hairs; stems 0.5–3 dm tall
        • 12a. Corolla 10–15 mm wide; leaf blades cordate-orbicular to reniform, 5–10 mm long; bracteal leaves gradually reduced in size from foliage leaves (i.e., the flowers appearing axillary)
        • 12b. Corolla 4–10 mm wide; leaf blades lanceolate or elliptic to ovate, 10–40 mm long; bracteal leaves abruptly reduced in size from foliage leaves (i.e., the flowers appearing in racemes)
          • 13a. Capsule 4–7 mm tall, taller than wide; stems erect, pilose in the apical portion; plants of alpine communities
          • 13b. Capsule 3–4 mm tall, wider than tall; stems creeping at the base or producing prostrate lower branches, minutely puberulent; plants predominantly of human-disturbed communities, sometimes in low-elevation forests
    • 9b. Plants annual, from fibrous roots

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