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Key to Duravia

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1 Pedicels deflexed; leaves not plicate, revolute at the margin; [a rare exotic waif in our area]
1 Pedicels erect-ascending; leaves plicate with one fold on either side of the midrib, planar at the margin; [widespread native in our area]

Key to Polygonum

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1 Flowers in terminal or long-peduncled axillary racemes; branches adnate to stems, therefore appearing to arise internodally; plants suffrutescent bushy herbs
1 Flowers in small clusters or very reduced racemes of 1-5 flowers, borne in the axils of normally sized or reduced leaves; branches not adnate to the stem, and thus arising at nodes; plants erect or sprawling herbs.
  2 Stems with 4 obscure ribs or angles (or lacking apparent ribs); leaf venation parallel, with inconspicuous secondary veins, longitudinally plicate or not; anthers pink-purple; [section Duravia].
    3 Pedicels deflexed; leaves not plicate, revolute at the margin; [a rare exotic waif in our area]
    3 Pedicels erect-ascending; leaves plicate with one fold on either side of the midrib, planar at the margin; [widespread native in our area]
  2 Stems with 8-16 distinct ribs; leaf venation pinnate, the secondary veins apparent; anthers whitish yellow; [section Polygonum].
      4 Perianth bottle-shaped, constricted above the achene.
        5 Tepals keeled; fruiting perianth divided about 1/3 of its length; stem leaves (1-) avg. 1.6 (-3)× as long as branch leaves
        5 Tepals not keeled; fruiting perianth divided about ¾ of its length; stem leaves (1.5-) avg. 2.5 (-4)× as long as branch leaves
      4 Perianth more open, not constricted above the achene.
          6 Inflorescences spikelike, the cymules borne in the axils of bracts shorter than the cymules
          6 Inflorescences axillary, the cymules borne in the axils of leaves longer than the cymules (though often shorter than primary leaves of the stem).
             7 Ocreae pruinose; mature tepals notably white or pink, loosely spreading; achenes smooth, glossy; [of maritime situations]
             7 Ocreae not pruinose; mature tepals yellow-green, white, pink, or reddish, appressed to the achene; achenes either smooth and glossy or textured and dull; [mainly of inland and disturbed situations]; [P. aviculare complex].
               8 Outer 3 tepals cucullate, in fruiting condition distinctly surpassing the inner 2 sepals and concealing them.
                 9 Plants prostrate; leaves 2.5-5.6 (-10)× as long as wide
                 9 Plants ascending to erect; leaves 4-12× as long as wide.
                   10 Plants bluish green when fresh, turning dark brown to black when dried; leaves rounded or obtuse at the apex; pedicels 1-2 mm long; stem leaves 1-2.5 (-3.5)× as long as the branch leaves
                   10 Plants yellowish green when fresh, not darkening when dried; leaves acute to acuminate at the apex; pedicels 2.5-6 mm long; stem leaves 2.1-3.5 (-4.2)× as long as the branch leaves
               8 Outer 3 tepals flat, equaling or shorter than the inner 2 sepals.
                     11 Perianth tube 40-57% of the perianth length.
                       12 Tepals green, margins pink or red (rarely white), with branched veins; plants prostrate to ascending, with 3-15 stems; leaf blades 2.8-5.7 (-6.5)× as long as wide
                       12 Tepals green or reddish brown, margins white, with unbranched veins; plants usually ascending, with 1-7 stems; leaf blades (3.40) 4.2-9.2× as long as wide
                     11 Perianth tube 15-40% of the perianth length.
                          13 Leaf blades 2-4.5× as long as wide; perianth (2.3-) 2.8-4.7 (-5) mm long; achenes (of the early season) (2.1-) 2.7-3.7 mm long
                          13 Leaf blades (3.4-) 4.2-9.2× as long as wide; perianth 1.9-3.4 mm long; achenes (of the early season) 1.2-1.8 mm long