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See list of 10 genera in this family

References: Hong et al. (1998), Mitchell and Dean (1978), Ronse Decraene and Akeroyd (1988), Ronse Decraene et al. (2000).

  • 1a. Achenes trigonous and with 3 evident wing-angles; leaf blades 12–40 (–57) ×10–30 (–61) cm, cordate-ovate to deltate, borne on stout petioles; androecium with 9 stamens
  • 1b. Achenes lenticular or trigonous, but without wings or with an partially encircling, marginal wing on a lenticular achene in Oxyria; leaf blades shorter and/or narrower, with relatively thinner petioles; androecium with 3–8 stamens (9 in Chorizanthe)
    • 2a. Achenes with a partially encircling, marginal wing; perianth with 4 tepals
    • 2b. Achenes without wings; perianth with (4–) 5 or 6 tepals
      • 3a. Outer 3 tepals of carpellate flowers each with a conspicuous spine (note: this most evident in fruit); plants clearly monoecious—the carpellate flowers with 6 tepals positioned below the staminate ones with 5 tepals
      • 3b. None of the tepals bearing spines (though with a spiny involucre in Chorizanthe); plants predominantly synoecious or dioecious (sometimes polygamous), the two types of flowers (when present) with the same number of tepals
        • 4a. Flowers subtended by a 6-parted involucre, the involucre with 3 longer members alternating with 3 shorter members, each member tipped by an awn; androecium with 9 stamens
        • 4b. Flowers not subtended by an awn-tipped involucre; androecium with 3–8 stamens
          • 5a. Tepals 6, sepaloid or herbaceous, in 2 series of 3—the outer series spreading to reflexed, the inner series erect and distinctly enlarged in fruit (not accrescent in R. acetosella) [Figs. 801,803]
          • 5b. Tepals (4–) 5, often petaloid, usually in a single series, all erect to ascending, 
of ± equal size relative to one another in fruit or the outer tepals slightly larger than the inner [Figs. 792,794,797]
            • 6a. Tepals nearly distinct, remaining small in fruit; achene exserted beyond the remnant tepals for much of its length; filaments winged; nectaries stalked
            • 6b. Tepals connate at base for a distance up to 57% of their total length [Figs. 796,797], at least somewhat accrescent in fruit; achene enclosed in remnant tepals or the tip exserted; filaments unwinged; nectaries absent or present and then not stalked
              • 7a. Tepals with trifid veins (i.e., with three main branches at the base); flowers with nectaries, these appearing as mamillae around the stamens; stamens monomorphic, not enlarged at base
                • 8a. Tepals connate at the base for or less of their length; gynoecium with 3 carpels and 3 styles or the flowers sterile or replaced by bulbils; androecium with 8 stamens; plants perennial, with basally disposed leaves, unbranched stems, and a solitary, terminal inflorescence [Fig. 786]
                • 8b. Tepals connate for or more their length into a cup-like structure (except in P. wallichii); gynoecium with 2 or 3 carpels and 1 style that is apically bifid or trifid (with 2 styles in P. virginiana); androecium with 5–8 stamens; plants annual or perennial, with chiefly cauline leaves, unbranched or branched stems, and commonly 2 or more terminal or terminal and axillary inflorescences (commonly solitary and terminal in P. amphibian and P. coccinea)
              • 7b. Tepals with dendritic veins (i.e., with a single main vein that smaller veins branch off from) or sometimes the vein unbranched [Fig. 797]; flowers without nectaries; stamens dimorphic, the inner larger, often enlarged at the base
                • 9a. Erect to prostrate herbs up to 7 (–10) dm tall; stipules bilobed (usually not in P. articulatum); papillae absent from base of filaments; outer tepals keeled, but not winged, in fruit; flowers with 3–8 stamens
                • 9b. Robust, upright herbs 10–40 dm tall or vines; stipules truncate to obliquely pointed at apex (i.e., not bilobed); papillae present at the base of the filaments; outer tepals with a conspicuous keel or wing in fruit; flowers with 8 stamens

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