1	Flowers in axillary fascicles, if in spikes then with leaves; petioles articulate at base; ocrea membranous, 2-cleft or lacerate; filaments dilated at base (1. P. sect. Polygonum).		(2)
+	Inflorescence spicate, capitate, or paniculate; ocrea neither 2-cleft nor lacerate; petiole not articulate; filaments not dilated at base.		(17)
2 (1)	Subshrub or small shrub.		(3)
+	Annual or perennial herb.		(6)
3 (2)	Subshrub.		(4)
+	Small shrub.		(5)
4 (3)	Stems prostrate or ascending; leaves linear, green, apex spinose.		1 P. paronychioides
+	Stems erect; leaves elliptic or oblong, gray-green, apex not spinose.		3 P. schischkinii
5 (3)	Leaves orbicular or broadly elliptic, 1-1.3 cm wide; achenes densely granular puncticulate, slightly shiny.		2 P. intramongolicum
+	Leaves oblong or elliptic, 3-4 mm wide; achenes smooth, shiny.		4 P. popovii
6 (2)	Perennial herb; roots ligneous; petioles 2-5 mm.		5 P. cognatum
+	Annual herb; roots not ligneous; petioles very short or nearly absent.		(7)
7 (6)	Leaves linear or subulate.		(8)
+	Leaves lanceolate, oblanceolate, elliptic, or oblong.		(10)
8 (7)	Stems slender, glabrous; perianth membranous, cleft to 3/4; achenes biconvex, smooth, shiny.		13 P. molliiforme
+	Stems not slender, scabrous or papillate; perianth herbaceous, cleft to 1/3 or 1/2; achenes trigonous, punctate, slightly shiny.		(9)
9 (8)	Perianth cleft to 1/3; achenes densely punctate; flowers 1 or 2.		10 P. polycnemoides
+	Perianth cleft to 1/2; achenes slightly punctate; flower solitary.		15 P. acerosum
10 (7)	Stems erect; inflorescence spicate, terminal.		(11)
+	Stems prostrate, procumbent, ascending, or erect; flowers 1-7, in axillary fascicles.		(12)
11 (10)	Leaves caducous; achenes smooth, shiny.		12 P. argyrocoleon
+	Leaves not caducous; achenes densely punctate, slightly shiny.		11 P. patulum
12 (10)	Pedicels articulate at middle; achenes smooth, shiny.		9 P. plebeium
+	Pedicels articulate at apex; achenes densely punctate or granular-striate, opaque or slightly shiny.		(13)
13 (12)	Achenes densely granular-striate, opaque.		(14)
+	Achenes densely minutely punctate, slightly shiny.		(15)
14 (13)	Perianth cleft to 2/3-3/4; achenes included or slightly exceeding persistent perianth.		6 P. aviculare
+	Perianth cleft to 1/2; achenes included in persistent perianth.		8 P. arenastrum
15 (13)	Plant gray-green; ocrea silvery, with inconspicuous veins; achenes included in persistent perianth.		14 P. acetosum
+	Plant green; ocrea: lower part brownish, upper part white, membranous, with conspicuous veins; achenes exceeding persistent perianth.		(16)
16 (15)	Ocrea 5-9-veined; leaf blade adaxially with conspicuous midvein and lateral veins.		16 P. rigidum
+	Ocrea 3- or 4-veined; leaf blade adaxially with conspicuous midvein and inconspicuous lateral veins.		7 P. humifusum
17 (1)	Stems and petioles with retrorse prickles (6. P. sect. Echinocaulon).		(18)
+	Stems and petioles without retrorse prickles.		(31)
18 (17)	Ocrea expanding into green herbaceous wings at apex.		(19)
+	Ocrea not expanding into wings at apex.		(24)
19 (18)	Leaf blade triangular-peltate; perianth accrescent and fleshy in fruit.		100 P. perfoliatum
+	Leaf blade not triangular-peltate, perianth not accrescent nor fleshy in fruit.		(20)
20 (19)	Leaves triangular or narrowly triangular.		(21)
+	Leaves hastate or narrowly hastate.		(22)
21 (20)	Apex of ocrea with green reniform-orbicular wings; peduncles shortly glandular hairy.		104 P. senticosum
+	Apex of ocrea with green lanceolate-auriculate wings; peduncles not glandular hairy.		105 P. darrisii
22 (20)	Leaves narrowly hastate, both surfaces densely stellate hairy; wings of ocrea with dentate margin.		101 P. maackianum
+	Leaves hastate, both surfaces sparsely bristly, sometimes rarely stellate hairy; wings of ocrea with entire or crenate margin.		(23)
23 (22)	Perianth 5-parted; achenes trigonous.		102 P. thunbergii
+	Perianth 4-parted; achenes biconvex.		103 P. biconvexum
24 (18)	Apex of ocrea oblique, shortly ciliate or not ciliate.		(25)
+	Apex of ocrea truncate, long ciliate.		(28)
25 (24)	Apex of ocrea shortly ciliate; peduncles with glandular hairs; bracts funnel-shaped.		(26)
+	Apex of ocrea not ciliate; peduncles with or without glandular hairs; bracts elliptic.		(27)
26 (25)	Leaves lanceolate or narrowly oblong, base sagittate; apex acute; perianth 4-parted.		106 P. praetermissum
+	Leaves ovate-elliptic, base hastate or cordate, apex acuminate; perianth 5-parted.		107 P. dissitiflorum
27 (25)	Leaves basally sagittate; styles 3, connate to below middle; achenes ovoid, trigonous.		108 P. sagittatum
+	Leaves basally cuneate, truncate, or subhastate; styles 2, free, achenes nearly orbicular, biconvex.		109 P. dichotomum
28 (24)	Leaves basally cuneate; spikes interrupted at base; bracts funnel-shaped; peduncles densely glandular hairy.		110 P. bungeanum
+	Leaves basally not cuneate; spikes not interrupted; bracts elliptic or ovate; peduncles densely pubescent and sparsely glandular hairy.		(29)
29 (28)	Leaves ovate or oblong-ovate; inflorescence spicate, several spikes aggregated, becoming panicle-like.		111 P. muricatum
+	Leaves lanceolate or elliptic; inflorescence spicate, not aggregated nor panicle-like.		(30)
30 (29)	Leaves basally weakly cordate, truncate, or subsagittate; base of ocrea with dense retrorse prickles; pedicels 1-2 mm, glabrous.		112 P. strigosum
+	Leaves basally sagittate or subhastate; base of ocrea without retrorse prickles; pedicels 4-6 mm, with glandular hairs.		113 P. hastatosagittatum
31 (17)	Inflorescence spicate.		(32)
+	Inflorescence capitate or paniculate.		(76)
32 (31)	Stems branched, without basal leaves, sometimes with slender horizontal rhizomes; apex of ocrea truncate, usually ciliate; annual or perennial herb (2. P. sect. Persicaria).		(33)
+	Stems simple, rarely branched, with basal leaves; rhizomes ligneous, large, usually curved; apex of ocrea oblique, not ciliate; perennial herb, subshrub, or small shrub (3. P. sect. Bistorta).		(55)
33 (32)	Perennial herb.		(34)
+	Annual herb.		(38)
34 (33)	Amphibious plant; leaves of aquatic plants oblong, basally subcordate; those of terrestrial plants lanceolate, basally rounded.		17 P. amphibium
+	Terrestrial plant; leaves lanceolate, basally cuneate, rarely subrounded.		(35)
35 (34)	Leaf blade sericeous on both surfaces; cilia of ocrea 4-6 mm.		(36)
+	Leaf blade appressed hispidulous or pubescent on both surfaces; cilia of ocrea 1-2 cm.		(37)
36 (35)	Leaves narrowly cuneate at base; achenes orbicular, biconvex; styles 2, free.		18 P. pulchrum
+	Leaves cuneate at base; achenes ellipsoid, trigonous; styles 3, connate below middle.		19 P. huananense
37 (35)	Cilia of ocrea 1-1.2 cm; stems glabrous, sometimes sparsely hispidulous; leaf blade sparsely appressed hispidulous on both surfaces; achenes 2.5-3 mm.		20 P. japonicum
+	Cilia of ocrea 1.5-2 cm; stems pubescent; leaf blade pubescent on both surfaces; achenes 1.5-2 mm.		21 P. barbatum
38 (33)	Plant glabrous throughout.		22 P. glabrum
+	Plant not glabrous throughout.		(39)
39 (38)	Peduncles glandular hairy or glandular.		(40)
+	Peduncles not glandular hairy and glandular.		(43)
40 (39)	Peduncles glandular hairy.		(41)
+	Peduncles glandular.		(42)
41 (40)	Peduncles, stems, and branches densely glandular hairy and hirsute; achenes trigonous.		23 P. viscosum
+	Peduncles sparsely glandular hairy or glabrous; stems and branches sparsely pubescent or glabrescent; achenes biconvex, rarely trigonous.		24 P. persicaria
42 (40)	Peduncles sparsely viscid-glandular; perianth 5(or 4)-parted; achenes ovoid, trigonous.		25 P. viscoferum
+	Peduncles glandular; perianth 4(or 5)-parted; achenes broadly ovoid, biconcave.		26 P. lapathifolium
43 (39)	Apex of ocrea usually with green leaflike wing; leaf blade 5-12 cm wide.		27 P. orientale
+	Apex of ocrea without wing; leaf blade 0.3-4 cm wide.		(44)
44 (43)	Leaves dark blue-green when dry.		(45)
+	Leaves not dark blue-green when dry.		(46)
45 (44)	Leaves ovate or broadly elliptic, apex obtuse or slightly acute; achenes broadly ovoid, trigonous.		28 P. tinctorium
+	Leaves elliptic-ovate or broadly lanceolate, apex acute; achenes ovoid, biconvex.		29 P. assamicum
46 (44)	Perianth punctate.		(47)
+	Perianth not punctate.		(49)
47 (46)	Leaves ovate, 1-2.5 cm; tepals 4-5 mm.		30 P. paralimicola
+	Leaves lanceolate, 4-10 cm; tepals 2-3 mm.		(48)
48 (47)	Stems glabrous; perianth white or pink above; leaves with peppery taste.		31 P. hydropiper
+	Stems sparsely hispidulous; perianth red above; leaves without peppery taste.		32 P. pubescens
49 (46)	Spikes dense, not interrupted.		(50)
+	Spikes lax, slender, interrupted.		(52)
50 (49)	Leaves narrowly lanceolate, 4-8 mm wide; achenes biconvex, 1-1.5 mm.		37 P. kawagoeanum
+	Leaves elliptic-lanceolate or ovate-lanceolate, 10-25 mm wide; achenes trigonous, 2.5-3 mm.		(51)
51 (50)	Stems erect; leaves 6-10 cm, base cuneate; pedicels 7-8 mm.		38 P. jucundum
+	Stems stoloniferous, rooting from nodes; leaves 2-4 cm, base broadly cuneate; pedicels 5-6 mm.		39 P. limicola
52 (49)	Cilia of ocrea 6-8 mm, achenes trigonous.		(53)
+	Cilia of ocrea 0.5-5 mm; achenes biconvex, rarely trigonous.		(54)
53 (52)	Leaves ovate-lanceolate or ovate, apex caudate-acuminate, base broadly cuneate.		33 P. posumbu
+	Leaves lanceolate or broadly lanceolate, apex acute or acuminate, base cuneate or rounded.		34 P. longisetum
54 (52)	Spikes to 10 cm, pendulous, interrupted; cilia of ocrea 3-5 mm.		35 P. taquetii
+	Spikes 3-5 cm, erect, interrupted below; cilia of ocrea 0.5-3 mm.		36 P. foliosum
55 (32)	Subshrub or small shrub.		(56)
+	Perennial herb.		(58)
56 (55)	Subshrub; leaves oblanceolate or lanceolate; spikes dense, 1-1.5 cm in diam.; tepals obovate.		59 P. affine
+	Small shrub; leaves elliptic or lanceolate; spikes lax, 0.5-0.8 cm in diam.; tepals elliptic.		(57)
57 (56)	Leaves elliptic, 1-2 cm; tepals narrowly elliptic; stamens exserted.		60 P. vacciniifolium
+	Leaves lanceolate, 3-15 cm; tepals broadly elliptic; stamens included.		61 P. emodi
58 (55)	Inflorescence lower part with bulbils.		(59)
+	Inflorescence without bulbils.		(60)
59 (58)	Basal leaves ovate or narrowly ovate; cauline leaves: upper ones sessile, clasping.		40 P. suffultoides
+	Basal leaves oblong, ovate-lanceolate or linear; cauline leaves not clasping.		41 P. viviparum
60 (58)	Basal leaves basally decurrent along petiole, forming wings or slightly decurrent.		(61)
+	Basal leaves basally not decurrent.		(69)
61 (60)	Basal leaves narrowly ovate or orbicular-ovate, 3-7 cm wide.		(62)
+	Basal leaves neither narrowly ovate nor orbicular-ovate, 1-3(-5) cm wide.		(63)
62 (61)	Basal leaves narrowly ovate, apex acute; cauline leaves clasping.		42 P. pacificum
+	Basal leaves orbicular-ovate, apex obtuse; cauline leaves not clasping.		43 P. honanense
63 (61)	Rhizomes horizontal, not curved; ocrea brown throughout, cleft to base.		44 P. sinomontanum
+	Rhizomes curved; ocrea: lower part green, upper part brown, cleft to middle.		(64)
64 (63)	Cauline leaves: upper ones clasping.		(65)
+	Cauline leaves: upper ones not clasping.		(66)
65 (64)	Leaves glabrous on both surfaces; basal leaves basally cuneate; cauline leaves auriculate; spikes 4-8 cm, ca. 1 cm in diam.		45 P. manshuriense
+	Leaves densely gray-white pubescent abaxially; basal leaves basally rounded or subcordate; cauline leaves not auriculate; spikes 2-3 cm, 1-1.5 cm in diam.		46 P. ochotense
66 (64)	Leaves subleathery; perianth purple-red, tepals 4-5 mm; styles 3, connate to below.		47 P. milletii
+	Leaves papery; perianth pinkish or white, tepals 2-3.5 mm; styles 3, free.		(67)
67 (66)	Spikes 2-3 cm, 1.5-2 in diam.; tepals 3-3.5 mm.		48 P. ellipticum
+	Spikes 4-8 cm, 0.8-1.2 in diam.; tepals 2-3 mm.		(68)
68 (67)	Basal leaves narrowly oblong or oblong-lanceolate, 1-2 cm wide.		49 P. alopecuroides
+	Basal leaves broadly lanceolate or narrowly ovate, 2-5 cm wide.		50 P. bistorta
69 (60)	Stems simple or branched; basal leaves ovate.		(70)
+	Stems simple; basal leaves not ovate.		(71)
70 (69)	Rhizomes usually torulose; stems slender; leaf margin not revolute, apex acuminate or acute.		51 P. suffultum
+	Rhizomes horizontal, not torulose; stems robust; leaf margin slightly revolute, apex long acuminate.		52 P. amplexicaule
71 (69)	Rhizomes horizontal; spikes lax, nutant; pedicels 10-12 mm, articulate at middle.		53 P. griffithii
+	Rhizomes curved; spikes erect; pedicels 3-6 mm, articulate at apex.		(72)
72 (71)	Basal leaves oblong or lanceolate; perianth pinkish or white, tepals 2-3 mm.		(73)
+	Basal leaves elliptic, ovate-elliptic, or ovate-lanceolate; perianth red or purple-red, tepals 3-5 mm.		(74)
73 (72)	Spikes 1.5-2.5 cm, 1-1.5 cm in diam.; basal leaves oblong, lanceolate, or linear-lanceolate; anthers black-purple.		54 P. macrophyllum
+	Spikes 4-6 cm, 0.8-12 cm in diam.; basal leaves narrowly oblong or lanceolate; anthers red-brown.		55 P. paleaceum
74 (72)	Leaf blade yellow-brown tomentose abaxially.		56 P. subscaposum
+	Leaf blade glabrous or sparsely pubescent.		(75)
75 (74)	Basal leaves elliptic, veins purple-red; styles 3, connate to below middle.		57 P. purpureonervosum
+	Basal leaves ovate-elliptic or ovate-lanceolate, veins green; styles 3, free.		58 P. coriaceum
76 (31)	Inflorescence capitate (4. P. sect. Cephalophilon).		(77)
+	Inflorescence paniculate (5. P. sect. Aconogonon).		(93)
77 (76)	Perennial herb.		(78)
+	Annual herb.		(85)
78 (77)	Leaves palmate.		62 P. palmatum
+	Leaves not palmate.		(79)
79 (78)	Ocrea glabrous, 1.5-3 cm, apex oblique; perianth accrescent in fruit, fleshy.		63 P. chinense
+	Ocrea glandular hairy or pilose, less than 1.2 cm, apex truncate; perianth not accrescent in fruit, not fleshy.		(80)
80 (79)	Stems creeping or prostrate.		(81)
+	Stems erect or decumbent.		(82)
81 (80)	Stems ligneous at base, tufted; leaves ovate or elliptic; petioles 2-3 mm; ocrea glandular hairy.		64 P. capitatum
+	Stems not ligneous at base, not tufted; leaves cordate or ovate-cordate; petioles 1-2 cm; ocrea pilose.		65 P. strindbergii
82 (80)	Leaves pinnatifid.		66 P. runcinatum
+	Leaves entire.		(83)
83 (82)	Leaves not decurrent at base; petioles not winged.		69 P. wallichii
+	Leaves decurrent at base; petioles winged.		(84)
84 (83)	Leaves ovate-oblong, apex long acuminate.		67 P. umbrosum
+	Leaves broadly ovate or triangular-ovate, apex acuminate.		68 P. microcephalum
85 (77)	Stems prostrate, tufted; leaves narrowly lanceolate or lanceolate.		70 P. criopolitanum
+	Stems erect or decumbent; leaves ovate or lanceolate-ovate.		(86)
86 (85)	Leaves sparsely long glandular hairy on both surfaces.		71 P. humile
+	Leaves pilose, strigose, or glabrous on both surfaces.		(87)
87 (86)	Peduncles with glandular hairs; petioles winged.		(88)
+	Peduncles without glandular hairs; petioles not winged.		(89)
88 (87)	Leaves sparsely pellucid yellow glandular punctate; petioles winged; bracts glabrous.		72 P. nepalense
+	Leaves not glandular punctate; petioles narrowly winged; bracts sparsely glandular hairy.		73 P. glaciale
89 (87)	Perianth 4-parted.		(90)
+	Perianth 5-parted.		(91)
90 (89)	Leaves obovate or elliptic, 3-6 mm, both surfaces glabrous or sparsely pilose abaxially.		77 P. fertile
+	Leaves ovate, 1-1.5 cm, both surfaces pilose.		78 P. sparsipilosum
91 (89)	Leaves ovate, 4-8 mm, glabrous, base cordate; petioles short or nearly absent.		74 P. delicatulum
+	Leaves ovate or lanceolate-ovate, 1-3 cm, strigose or pilose, base cuneate or subtruncate; petioles 3-10 mm.		(92)
92 (91)	Leaves strigose on both surfaces; stamens 3 or 4.		75 P. filicaule
+	Leaves pilose or glabrescent on both surfaces; stamens 8.		76 P. cyanandrum
93 (76)	Subshrub.		(94)
+	Perennial herb.		(97)
94 (93)	Perianth accrescent and fleshy in fruit, tepals elliptic; leaves elliptic or elliptic-lanceolate, base cuneate.		79 P. molle
+	Perianth not accrescent nor fleshy in fruit, tepals obovate; leaves not elliptic nor elliptic-lanceolate, base rounded, cordate, or truncate, but cuneate in P. tibeticum.		(95)
95 (94)	Branches forked; leaves subsessile, ovate, base rounded or subcordate.		80 P. tortuosum
+	Branches not forked; leaves petiolate, lanceolate, elliptic, or oblong, base hastate-cordate, subtruncate, or cuneate.		(96)
96 (95)	Panicle spreading; leaves broadly lanceolate or oblong-lanceolate, or narrowly lanceolate or narrowly oblong, 6-17 cm, base hastate-cordate or subtruncate.		81 P. polystachyum
+	Panicle not spreading; leaves elliptic or obovate-oblong, 3-5 cm, base cuneate.		82 P. tibeticum
97 (93)	Stems creeping, forming tufts; leaves orbicular or reniform.		(98)
+	Stems erect; leaves not orbicular or reniform.		(99)
98 (97)	Leaves 0.3-0.5 cm in diam., base rounded; tepals elliptic; achenes broadly ovoid, biconvex.		83 P. nummulariifolium
+	Leaves 1-4 cm in diam.; base cordate; tepals obovate; achenes ellipsoid, trigonous.		84 P. forrestii
99 (97)	Stems simple, with basal leaves; flowers unisexual and plants dioecious.		85 P. hookeri
+	Stems branched, without basal leaves; flowers bisexual.		(100)
100 (99)	Leaves ovate.		(101)
+	Leaves elliptic or lanceolate to linear, or oblong, but narrowly ovate to broadly ovate in P. campanulatum.		(104)
101 (100)	Perianth red; pedicels articulate at middle.		86 P. songaricum
+	Perianth white; pedicels articulate at apex or not articulate.		(102)
102 (101)	Pedicels 3-4 mm, not articulate or ?articulate; achenes equaling persistent perianth.		87 P. coriarium
+	Pedicels 1-2 mm, articulate at apex; achenes distinctly exceeding persistent perianth.		(103)
103 (102)	Leaves basally cuneate, petioles short or nearly absent; achenes usually erect.		88 P. platyphyllum
+	Leaves basally rounded, petioles 2-4 cm; achenes pendulous.		89 P. limosum
104 (100)	Leaves basally usually hastate.		90 P. sibiricum
+	Leaves basally not hastate.		(105)
105 (104)	Tepals obovate, 3-4 mm wide.		(106)
+	Tepals elliptic, 2-3 mm.		(109)
106 (105)	Leaf blade usually constricted below, base truncate or cuneate; bracts 1-1.5 cm; pedicels pubescent.		96 P. pinetorum
+	Leaf blade not constricted below, base broadly cuneate; bracts 2-3 mm; pedicels glabrous.		(107)
107 (106)	Pedicels articulate at apex; styles ca. 2 mm.		97 P. campanulatum
+	Pedicels not articulate at apex; styles ca. 0.5 mm.		(108)
108 (107)	Leaf blade abaxially densely grayish tomentose.		98 P. lichiangense
+	Leaf blade abaxially pilose.		99 P. cathayanum
109 (105)	Achenes distinctly exceeding persistent perianth.		(110)
+	Achenes included in persistent perianth.		(111)
110 (109)	Stems branched from above middle, usually sparsely hirsute; branches not divaricate; leaves ovate-lanceolate or lanceolate, base broadly cuneate.		94 P. alpinum
+	Stems branched from base, glabrous; branches divaricate; leaves lanceolate or oblong, base cuneate or narrowly cuneate.		95 P. divaricatum
111 (109)	Leaves linear, 2-4 mm wide, margin conspicuously revolute.		91 P. angustifolium
+	Leaves lanceolate 5-15 mm wide, margin not revolute.		(112)
112 (111)	Leaves lanceolate or linear lanceolate, 5-8 mm, base narrowly cuneate.		92 P. ocreatum
+	Leaves lanceolate or broadly lanceolate, 8-15 mm wide, base broadly cuneate.		93 P. ajanense