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Key to Alismataceae

Alismataceae

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1 Pistils in a single whorl, borne on a flat receptacle; stamens 6; inflorescence compound, many of the primary nodes bearing whorled branches which in turn bear whorled branches or whorled flowers
1 Pistils spiraled in several to many whorls, borne on a globose receptacle; stamens 6-many; inflorescence either racemose (or in some species of both Echinodorus and Sagittaria somewhat compound, with the lowermost node or two bearing branches which in turn bear whorled flowers) or umbellate (Hydrocleys).
  2 Scape septate; fruits follicles
  2 Scape not septate; fruits achenes.
    3 Achenes flattened, with winged margins and often also with irregular corky ornamentations on the faces; flower whorls subtended by 3 bracts, with no additional bracteoles
    3 Achenes turgid, with ribs or ridges; flower whorls subtended by 3 bracts and additional bracteoles.
      4 Leaf blades 5-20 cm long, 3-15 cm wide; achenes (pistils) 45-250 per head; stamens ca. 21; petals 6-12 mm long, scapes 20-120 cm tall, erect or arching/reclining
      4 Leaf blades 1-3 cm long, 0.2-2 cm wide; achenes (pistils) 10-20 per head; stamens 6 or 9; petals 1-3 mm long; scapes 5-10 cm tall, erect