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See list of 7 species in this genus

Reference: Grau and Merxmüller (1972).

  • 1a. Calyx pubescent with erect to appressed hairs that are not hooked at the tip [Fig. 499]; plants commonly of wet-mesic to hydric soils, even growing in shallow water
    • 2a. Limb of the corolla 2–5 mm wide; mericarps taller than the style; stems terete, not stoloniferous; calyx usually deciduous in fruit, with the lobes approximately as long as or longer than the basal connate portion
    • 2b. Limb of the corolla 5–10 mm wide; mericarps shorter than the style; stems angled, often stoloniferous; calyx usually persistent in fruit, with the lobes shorter than the basal connate portion (rarely the lobes and connate portion approximately equal)
  • 1b. Calyx pubescent, at least in part with spreading, uncinate hairs [Fig. 498]; plants of xeric to mesic soils, typically found in fields, disturbed lots, and along roads (though sometimes invading forest floors)
    • 3a. Limb of corolla 1–2 mm wide in life; fruiting pedicels up to 3.5 mm long, shorter than the associated calyx
      • 4a. Calyx 4–7 mm long, weakly zygomorphic, 2 or 3 of the lobes shorter than and separated by a gap from the other ones; corolla white
      • 4b. Calyx 3–5 mm long, ± actinomorphic; corolla usually blue or yellow changing to blue
        • 5a. Inflorescence occupying much of the total height of the plant, the lower flowers scattered among the leaves; adaxial surface of leaf blades (at least along the midvein) with uncinate hairs; style surpassed by the mature mericarps; corolla blue
        • 5b. Inflorescence occupying about half or less of the total height of the plant, the lower flowers not from the axils of leaves or sometimes the lowest 1 or 2 flowers subtended by leafy bracts; adaxial surface of the leaf blades lacking uncinate hairs (though other types of hairs may be present); style often surpassing the mature mericarps; corolla at first yellow, then usually changing to blue
    • 3b. Limb of corolla 2–8 mm wide in life; fruiting pedicels 3–9 mm long, equal in length or longer than the associated calyx

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 Show photos of:   Each photo represents one species in this genus.