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Persicaria
See list of 22 species in this genusReference: Hinds and Freeman (2005).
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1a. Inflorescence panicle-like; perianth subrotate; tepals connate less than 20% of their total length
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1b. Inflorescence raceme-like (sometimes consisting of few flowers and ± capitate or sometimes appearing panicle-like when the upper plant is highly branched); perianth campanulate to narrow-campanulate; tepals connate 25–66% of their total length
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2a. Leaf blades extending down the petioles as a wing of tissue that clasps the stem (petiole sometimes only distally winged in P. chinensis); achenes conspicuously cellular-reticulate with longitudinal rows of aereolae
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3a. Flowers with 2 styles; achenes biconvex; abaxial surface of leaf blade glandular-punctate; peduncle stipitate-glandular near apex just below flowers
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3b. Flowers with 3 styles; achenes trigonous; abaxial surface of leaf blade without glandular dots; peduncle stipitate-glandular throughout
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2b. Leaf blades without winged petioles, not clasping the stem; achenes lacking a conspicuous cellular-reticulate pattern
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4a. Stems armed with reflexed prickles [Fig. 791]; principal leaf blades hastate or sagittate at base (sometimes truncate in P. perfoliata) [Fig. 791]; flowers comparatively few, in a short to capitate raceme-like inflorescence 0.4–2 (–3) cm long
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5a. Sheathing stipules apically foliaceous and expanded; leaf blades subpeltate; perianth persistent in fruit, forming a thickened, blue covering over the achene
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5b. Sheathing stipules scarious or hyaline, not expanded upward; leaf blades basifixed; perianth persistent in fruit, but neither thickened nor blue
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6a. Leaf blades lanceolate to elliptic, 5–31 mm wide, sagittate at the base, the basal lobes directed backward; peduncles glabrous; styles trifid, 1–1.5 mm long; achenes trigonous, 3–3.5 mm long
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6b. Leaf blades deltate, 10–150 mm wide, hastate at the base, the basal lobes divergent [Fig. 791]; peduncles hispid, often stipitate-glandular as well; styles bifid, 0.5–0.6 mm long; achenes biconvex, 3.5–5 mm long
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4b. Stems unarmed; leaf blades cuneate to cordate at base, lacking prolonged basal lobes; flowers usually many, in an elongate raceme-like inflorescence 1–50 cm long
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7b. Styles wanting or up to 2 mm long (up to 4 mm long in short-stamened flowers of P. amphibia), deciduous in fruit, not hooked at tip; perianth 5-merous, accrescent in fruit; flowers ascending to spreading (rarely the short pedicels drooped)
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8a. Plants perennial with rhizomes or stolons
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9a. Inflorescence terminal, solitary or paired, densely flowered, mostly 10–20 mm wide; tepals deep pink to red
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10a. Widest leaf blades 17–29 (–32) mm wide; principal emersed leaves with petioles 1–9 mm long, commonly with small, red-brown spots due to infection by Puccinia polygoni-amphibii, usually green in drying; primary inflorescences 13–28 (–30) mm long; floating leaf blades cuneate to rounded (infrequently truncate) at the base; rhizome 1.5–3.5 mm thick between leafless nodes, bearing few-branched to moderately branched roots; stipules of emersed shoots usually developing sheathing stipules with a foliaceous, outward-flange at the summit, these pubescent with wide-ascending to spreading hairs
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10b. Widest leaf blades (23–) 32–63 mm wide; principal emersed leaves with petioles 5–28 (–38) mm long, lacking the mentioned fungal infection, usually tinged with red or brown in drying; primary inflorescences (25–) 29–90 mm long; floating leaf blades cordate to rounded at the base; rhizome (2.8–) 3–6.5 mm thick between leafless nodes, bearing highly branched roots; sheathing stipules of emersed shoots without a green, outward flange, glabrous or pubescent with appressed hairs
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9b. Inflorescence terminal and often also axillary, often remotely flowered at the base, mostly 2–5 mm wide; tepals pink, white, and/or green
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11a. Tepals spotted with numerous yellow to brown or red-brown glandular dots [Fig. 794]
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12a. Inflorescence relatively sparsely flowered, usually interrupted in the basal portion with non-overlapping bracteoles; bracteoles subtending the pedicels (i.e., ocreolae) long-ciliate with hairs (0.2–) 0.3–1.9 (–2.2) mm long; leaf blades 6–24 mm wide (in part)
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12b. Inflorescence relatively densely flowered, usually continuous throughout with contiguous or even overlapping bracteoles (rarely the lowest nodes separate); bracteoles subtending the pedicels usually eciliate or sometimes the lower bracteoles with short cilia up to 0.4 (–1) mm long; leaf blades 20–45 mm wide
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11b. Tepals not spotted with glandular dots (rarely with a few, pale, scale-like glands in P. hydropiperoides, but these not providing an even dotting over the tepals)
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13a. Hairs of sheathing stipules (i.e., ocreae) gradually enlarged at base, adnate to stipule for 28–66% of their total length; perianth usually pink to red or cream-white (rarely purple or green-white to green)
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13b. Hairs of the sheathing stipules conspicuously enlarged at base, adnate to the stipule for (0–) 13–28% of their total length; perianth green-white to green
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8b. Plants annual from fibrous roots and/or a taproot
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14a. Sheathing stipules (i.e., ocreae) lacking a prominent ring of cilia around the summit, sometimes lacerate into segments in age
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15a. Perianth consisting of 4 (–5) tepals; tepals conspicuously 3-nerved, each nerve forking near the end into 2 recurved branches [Fig. 792]; inflorescence relatively slender, 5–11 mm wide, the axis often arched or drooping
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15b. Perianth consisting of 5 tepals; tepals obscurely nerved; inflorescence relatively thick, 10–15 mm wide, the axis usually straight or with a slight arch
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14b. Sheathing stipules ciliate with a prominent ring of bristles around the summit [Fig. 793]
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16a. Tepals spotted with numerous yellow to brown glandular dots [Fig. 794]
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17a. Perianth consisting of 4 (–5) tepals; inflorescences terminating the main stem and often axillary, commonly with overlapping bracteoles (i.e., ocreolae), interrupted by small leaves; achenes dull
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17b. Perianth consisting of 5 tepals; inflorescences terminating the main stem or branches, commonly with non-overlapping bracteoles (at least in the basal portion), without small leaves; achenes lustrous (in part)
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16b. Tepals not spotted with glandular dots [Fig. 792]
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18a. Leaf blades ovate, 3–16 cm wide; sheathing stipules horizontally divergent at the summit creating a conspicuous flange
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18b. Leaf blades narrow-lanceolate to elliptic or oblanceolate, 1–3 (–4) cm wide; sheathing stipules without a horizontally spreading summit
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19a. Upper portion of the stem and peduncles stipitate-glandular; inflorescence 3–10 cm long, lax or drooping
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19b. Upper portion of the stem and peduncles without stipitate glands; inflorescence 1–4.5 (–6.5) cm long, commonly erect to ascending
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20a. Sheathing stipules long-ciliate with marginal hairs (3–) 4–12 mm long; bracteoles of the flowers long-ciliate with marginal hairs (0.5–) 1–4 (–6) mm long; achenes trigonous
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20b. Sheathing stipules ciliate with marginal hairs (0.3–) 1–3.5 (–5) mm long [Fig. 793]; bracteoles of the flowers short-ciliate with marginal hairs (0.1–) 0.2–2 (–2.7) mm long; achenes biconvex or both biconvex and trigonous in the same inflorescence
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21a. Inflorescence loose and usually interrupted in the basal portion, 2–4 mm wide; leaf blades linear to narrow-lanceolate, (2–) 4–10 (–23) mm wide
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21b. Inflorescence dense, usually uninterrupted, 4–12 mm wide; leaf blades lanceolate to narrow-ovate, (2–) 10–25 (–40) mm wide
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22a. Inflorescence 6–12 mm wide, obloid to short-cylindrical; tepals 2–3 mm long at anthesis, enlarging in fruit and then up to 4 mm long, prominently, but minutely, patterned with a raised reticulum near the base; leaf blades commonly with a purple blotch on the adaxial surface [Fig. 793]
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22b. Inflorescence 4–7 mm wide, cylindrical to subconical; tepals 1.8–2 mm long at anthesis, enlarging in fruit and then up to 2.6 mm long, faintly reticulate-patterned, if at all, near the base; leaf blades usually unblotched
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Each photo represents one species in this genus.