1	Spikes on an axillary peduncle, several together in an umbel-like cluster, rarely solitary		60 Piper umbellatum
+	Spike leaf-opposed, rarely terminal, never axillary, solitary.		(2)
2 (1)	Leaf blade with very clearly defined, reddish brown glands, mainly along veins abaxially, uniformly dispersed adaxially		26 Piper thomsonii
+	Leaf blade with glands colorless or apparently absent.		(3)
3 (2)	Infructescences globose or nearly so, never more than 2 × as long as wide.		(4)
+	Inflorescences cylindric, more than 3 × as long as wide (usually much more).		(6)
4 (3)	Petioles and leaves very finely powdery pubescent abaxially along veins; stigmas 2		26 Piper thomsonii
+	Petioles and leaves glabrous; stigmas 3 or 4.		(5)
5 (4)	Flowers bisexual; ovaries free from rachis; leaf blade 7.5-16 cm; peduncles shorter than or ca. as long as petioles		4 Piper mullesua
+	Flowers unisexual, dioecious; ovaries and berries immersed in and connate to rachis; leaf blade 5-6 cm; peduncles ca. 4 × as long as petioles		58 Piper pleiocarpum
6 (3)	Bracts oblong, spatulate-oblong, or obovate-oblong, adnate to rachis with only sides and apex free.		(7)
+	Bracts orbicular, peltate with free margin all round.		(20)
7 (6)	Leaves pubescent at least abaxially on larger veins.		(8)
+	Leaves glabrous on both surfaces.		(9)
8 (7)	Branches glabrous; leaf apex abruptly narrowed and mucronate; petiole 3-3.5 cm or longer; peduncles shorter than petioles		6 Piper attenuatum
+	Branches densely pubescent; leaf apex acuminate; petiole 0.5-1.5 cm; peduncles longer than petioles		7 Piper pingbienense
9 (7)	Veins palmate or subpalmate, all arising less than 5 mm from base.		(10)
+	Veins pinnate, with 1 or more separating from each side of midvein more than 5 mm from base.		(12)
10 (9)	Inflorescences 1.5-5 cm; infructescences 3-3.5 cm, rachis conspicuously pale pilose		10 Piper mutabile
+	Inflorescences 7-27 cm; infructescences 10-22 cm, rachis indumentum inconspicuous.		(11)
11 (10)	Leaf base rounded to shortly cuneate; female inflorescences 7-17 cm, flowers developing unevenly; fruit smooth		12 Piper interruptum
+	Leaf base shallowly cordate; female inflorescences 14-23 cm, flowers developing evenly; fruit minutely rugulose or granular		9 Piper rhytidocarpum
12 (9)	Fruit with base narrowed into 1-4 mm stalk.		(13)
+	Fruit with base rounded, not narrowed into distinct stalk.		(15)
13 (12)	Leaves 5-veined, subbasal, apical pair parallel and adnate to midvein; infructescences 6-6.5 cm; fruit obovoid		17 Piper mischocarpum
+	Leaves 7-9-veined, apical pair arising 1.5-3 cm from base of blade; infructescences 16-37 cm; fruit globose or subglobose.		(14)
14 (13)	Peduncles longer than petioles; infructescences 29-37 cm; fruit stalks thick and strong, 1-2 mm		15 Piper stipitiforme
+	Peduncles shorter than petioles; infructescences ca. 16 cm; fruit stalks slender, 3-4 mm		16 Piper lingshuiense
15 (12)	Flowers polygamous, most with 2 stamens on opposite sides of ovary; infructescences dense; fruit globose, ± touching (cultivated)		5 Piper nigrum
+	Flowers unisexual, dioecious; infructescences very lax; fruit ovoid or fusiform, usually clearly separated (wild).		(16)
16 (15)	Leaves with 2 or more veins arising from each side of midvein above base of blade; fruit ± globose		13 Piper chaudocanum
+	Leaves with 1 pair of veins above base of blade; fruit ovoid to fusiform.		(17)
17 (16)	Leaf blade 4-9 cm wide; inflorescence rachis glabrous or nearly glabrous; fruit ovoid.		(18)
+	Leaf blade 3-5 cm wide; inflorescence rachis hairy; fruit fusiform.		(19)
18 (17)	Erect subshrubs; bracts ca. 1.5 × 0.8 mm		8 Piper polysyphonum
+	Climbers; bracts 5.5-6 × 1-1.5 mm		9 Piper rhytidocarpum
19 (17)	Inflorescences 1.5-5 cm; infructescences 3-3.5 cm; fruit smooth		10 Piper mutabile
+	Inflorescences 7-15 cm; infructescences to 22 cm; fruit minutely rugulose		11 Piper hainanense
20 (6)	Abaxial surface of leaves grayish white, with dense, sessile scales, otherwise glabrous; male inflorescences to 20 cm, grayish green		49 Piper tsengianum
+	Abaxial surface of leaves at most pale green, often darker, without any epidermal covering except sometimes scattered, simple hairs; inflorescences shorter or, if up to 20 cm, yellow.		(21)
21 (20)	Ovaries and fruit partly fused to rachis.		(22)
+	Ovaries and fruit free from rachis.		(42)
22 (21)	Fruits apically tomentose, completely fused to each other to form a nearly smooth, fleshy, cylindric mass (often cultivated)		24 Piper betle
+	Fruit glabrous, distinct, sometimes very soft when fully ripe and then difficult to separate when pressed and dried.		(23)
23 (22)	Erect subshrubs; fruit tuberculate-rugulose		25 Piper yunnanense
+	Stoloniferous herbs, vines, or scandent shrubs; fruit smooth.		(24)
24 (23)	Stoloniferous herbs on ground, occasionally clambering over rocks; fertile branches erect; leaves very finely powdery pubescent abaxially, clearly petiolate, base never clasping, outermost veins often ± pedately divided; female spikes erect		23 Piper sarmentosum
+	Climbers growing on trees or steep rock faces; branches often pendulous; leaves usually glabrous and with outermost veins not dividing above base (if very finely powdery pubescent, then apical leaves often nearly sessile with base cordate and clasping and female spikes reflexed)		22 Piper longum
25	Leaves with veins all basal or nearly basal and all arising less than 3 mm from base of blade.		(26)
+	Leaves with 2 or more lateral veins arising more than 1 cm from base of blade.		(29)
26 (25)	Inflorescences bisexual; leaf blade thinly papery to membranous, base cuneate		2 Piper chinense
+	Inflorescences unisexual; leaf blade papery to nearly leathery, base usually cordate.		(27)
27 (26)	Leaves densely brown pubescent, nearly tomentose, basal lobes overlapping		18 Piper submultinerve
+	Leaves glabrous or abaxially very finely powdery pubescent, basal lobes not overlapping.		(28)
28 (27)	Leaves very finely powdery pubescent abaxially; apical leaves often nearly sessile, base cordate and clasping; leaves with outermost veins often ± pedately divided		22 Piper longum
+	Leaves glabrous; apical leaves clearly petiolate, base subcordate to ± rounded; leaves with outermost veins not dividing above base		45 Piper austrosinense
29 (25)	Leaves pubescent or hispidulous, at least on veins and/or petioles.		(30)
+	Leaf blade and petiole glabrous or very finely powdery pubescent along veins (individual hairs hardly visible through ordinary hand lens).		(35)
30 (29)	Base of leaf blade rounded to truncate; female peduncles sometimes thickened upward.		(31)
+	Base of leaf blade cordate, usually deeply so; female peduncles not thickened upward.		(32)
31 (30)	Female peduncles uniform in thickness		43 Piper ponesheense
+	Female peduncles thicker toward apex		33 Piper puberulilimbum
32 (30)	Base of leaf blade ± symmetric; female spikes ca. 3 cm in fruit; peduncles shorter than petioles, rachis glabrous		19 Piper cathayanum
+	Base of leaf blade clearly asymmetric; female spikes 6-8 cm in fruit; peduncles longer than petioles, rachis roughly pubescent.		(33)
33 (32)	Leaf blade abaxially conspicuously densely brown pubescent, nearly tomentose; infructescences 1-1.7 cm thick		21 Piper infossum
+	Leaf blade abaxially hispidulous along veins to uniformly pubescent; infructescences 0.7-0.9 cm thick.		(34)
34 (33)	Leaf blade uniformly pubescent or hispidulous at least abaxially		18 Piper submultinerve
+	Leaf blade hispidulous along veins only		20 Piper semiimmersum
35 (29)	Leaves with 4 or more lateral veins arising above base from each side of midvein (cultivated)		59 Piper retrofractum
+	Leaves with only 2 lateral veins arising from midvein above base.		(36)
36 (35)	Female spikes 2-5 cm at anthesis, rachis and bracts glabrous.		(37)
+	Female spikes 6-10 cm at anthesis, to 30 cm in fruit, rachis and abaxial surfaces of bracts hairy.		(39)
37 (36)	Leaves elliptic or oblong, clearly oblique at base, one side broad and obtuse, other side narrow and cuneate		46 Piper senporeiense
+	Leaves ovate, elliptic, or ovate-lanceolate, only slightly asymmetric at base.		(38)
38 (37)	Male spike 2-5 cm; female spike 1.5-3 cm; leaf blade obtuse or shortly tapered at base		44 Piper infossibaccatum
+	Male spike 5-12 cm; female spike 3-3.5 cm; leaf blade cordate at base		21 Piper infossum
39 (36)	Bracts ciliate; female spikes 25-30 cm		42 Piper tsangyuanense
+	Bracts not ciliate; female spikes 1.5-15 cm.		(40)
40 (39)	Leaf apex rounded to subacute; bracts obovate, ca. 1.5 mm		40 Piper yui
+	Leaf apex acute to long acuminate; bracts orbicular, ca. 1 mm.		(41)
41 (40)	Leaf blade bullate, base shallowly cordate; apical pair of lateral veins arising 1-2(-2.7) cm from leaf base		20 Piper semiimmersum
+	Leaf blade flat, base cuneate to rounded; apical pair of lateral veins arising 3-6 cm from leaf base		47 Piper nudibaccatum
42 (21)	Base of fruit narrowed into distinct stalk more than 1 mm; leaf base obliquely cordate, usually with overlapping ears, abaxially villous, lateral veins up to 9 on each side of midvein		14 Piper laetispicum
+	Base of fruit rounded to cuneate, not forming stalk; leaf not as above, lateral veins never more than 4 on one side.		(43)
43 (42)	Rachis of inflorescence with conspicuous orange to yellow hairs visible between bracts; fruit rugulose, 3-5(-7) mm, not closely packed.		(44)
+	Rachis of inflorescence glabrous or with colorless hairs; fruit smooth or rugulose, 1.5-3 mm, often closely packed and ± angular.		(45)
44 (43)	Leaves papery, veins 7; stigmas 4 or 5, linear; fruit ± rounded at apex		35 Piper macropodum
+	Leaves leathery, veins 5(-7); stigmas 3 or 4, ovate-lanceolate; fruit acute at apex		57 Piper suipigua
45 (43)	Leaves hairy, at least abaxially along veins (hairs clearly visible at × 6 magnification or less).		(46)
+	Leaves glabrous throughout blade or very finely powdery pubescent or papillate (hairs or papillae visible at × 10 magnification or more); stems and petioles sometimes hairy.		(57)
46 (45)	Leaves abaxially densely pubescent, nearly tomentose, with most hairs obviously branched; bracts with 2-5 long hairs near apex abaxially		28 Piper bonii
+	Leaves more sparsely hairy, most hairs unbranched, especially away from main veins; bracts glabrous abaxially.		(47)
47 (46)	Flowers bisexual		1 Piper hochiense
+	Flowers unisexual, dioecious.		(48)
48 (47)	Erect subshrubs; leaves with at least 3 lateral veins arising more than 5 mm from base of midvein.		(49)
+	Climbers; leaves with up to 2 lateral veins arising more than 3 mm from base of midvein, otherwise all basal.		(50)
49 (48)	Infructescences to 16 cm; leaf veins sparsely hairy, hairs ± colorless		36 Piper boehmeriifolium
+	Infructescences to 30 cm; leaf veins densely hairy, hairs reddish brown		37 Piper dolichostachyum
50 (48)	Bracts 3-colored when dry: a black center (ca. 1 mm in diam.) surrounded by narrow, thickened, white band and thinner, pale yellow margin		34 Piper tricolor
+	Bracts uniformly colored or 2-colored with narrow, pale margin when dry.		(51)
51 (50)	Leaf base rounded to shortly tapered, if emarginate, then sinus narrower than petiole.		(52)
+	Leaf base cordate (rarely leaves at apices of flowering branches not cordate), sinus much wider than petioles.		(53)
52 (51)	Leaves abaxially with hairs nearly completely restricted to veins with very few between; peduncles ca. as long as petioles		51 Piper kadsura
+	Leaves abaxially uniformly hairy, often distinctly gray; peduncles ca. 2 × as long as petioles		50 Piper wallichii
53 (51)	Leaf base obliquely lobed, 8- or 9-veined; petiole ca. 2 mm		32 Piper yinkiangense
+	Leaf base cordate, 5- or 7-veined; petiole ca. 10 mm or longer.		(54)
54 (53)	Leaf blade with lateral veins all ± basal; stigma lobes 4-7		31 Piper taiwanense
+	Leaf blade with apical 2 lateral veins arising more than 5 mm above base; stigma lobes 3 or 4.		(55)
55 (54)	Leaves drying yellowish to pale brown, glabrous adaxially, pubescent abaxially, hairs sparse, not regularly curved		51 Piper kadsura
+	Leaves drying green to dark brown, roughly pubescent on both surfaces, hairs curved upward and hooklike.		(56)
56 (55)	Leaves often with some hairs branching; male inflorescences ca. as long as leaves; bracts with stalks longer than bract width; fruit rounded at apex		29 Piper hongkongense
+	Leaves with all hairs simple, non-branching; male inflorescences much longer than leaves; bracts with stalks shorter than bract width; fruit slightly sunken at apex		30 Piper sintenense
57 (45)	Leaves with all lateral veins arising less than 3 mm from base of blade		41 Piper arborescens
+	Leaves with 2 or more lateral veins arising 1 cm or more from base of blade.		(58)
58 (57)	Leaves with at least 4 lateral veins clearly arising above base of blade.		(59)
+	Leaves with not more than 3 lateral veins arising above base of blade.		(62)
59 (58)	Fruit ca. 4 mm in diam.; stems brown; leaves often drying gray-green		48 Piper flaviflorum
+	Fruit 1.2-3 mm in diam.; stems and leaves usually drying blackish.		(60)
60 (59)	Erect shrubs		36 Piper boehmeriifolium
+	Climbers.		(61)
61 (60)	Leaves 4-6 cm wide; bracts with stalks longer than bract width and longer than flowers, often conspicuously so		38 Piper pedicellatum
+	Leaves 7-12 cm wide; bracts with stalks shorter than bract width and shorter than flowers		39 Piper wangii
62 (58)	Leaves very finely powdery pubescent (magnification needed)		27 Piper sylvaticum
+	Leaves glabrous throughout.		(63)
63 (62)	Male spikes 8-21 cm; female or bisexual spikes 6-15 cm.		(64)
+	Male spikes 1.5-10 cm; female spikes 1.5-3.5(-6.5) cm.		(66)
64 (63)	Flowers bisexual; petiole 0.5-1 cm		3 Piper damiaoshanense
+	Flowers unisexual; petiole 1-3 cm.		(65)
65 (64)	Leaf base obliquely rounded (at least in leaves toward base of stem), apex acute to acuminate; drupe globose, apex rounded		48 Piper flaviflorum
+	Leaf base cuneate, apex long acuminate to caudate-acuminate; berries ovoid, apex sharp-pointed		57 Piper suipigua
66 (63)	Leaves 4- or 5-veined, apex long acuminate to caudate-acuminate.		(67)
+	Leaves 5-7-veined, apex acute to ± abruptly acuminate.		(68)
67 (66)	Leaves oblong or ovate-lanceolate; petiole 10-15 mm; veins curved adaxially, evidently prominent abaxially; bracts with long, pubescent stalks		55 Piper rubrum
+	Leaves lanceolate to narrowly lanceolate; petiole 4-6 mm; veins not curved adaxially; bracts ± sessile or with short, glabrous stalks		56 Piper bambusifolium
68 (66)	Male spikes 6-10 × ca. 0.2 cm, yellow, bracts ca. 0.8 mm in diam.; leaves 2.5-4.5 cm wide		54 Piper hancei
+	Male or bisexual spikes 3.5-5 × 0.25-0.4 cm at anthesis, ± green or white, bracts 1-1.5 mm in diam.; leaves 3.5-8 cm wide.		(69)
69 (68)	Leaf blade oblique at base, 7-12 cm wide.		(70)
+	Leaf blade symmetric at base, 2.5-8.5 cm wide.		(71)
70 (69)	Leaf blade with apical pair of lateral veins arising (2-)3-6.5 cm above base, nearly reaching apex of leaf (Yunnan)		39 Piper wangii
+	Leaf blade with apical pair of lateral veins arising 1-2 cm above base, alternate, reaching middle of leaf (Taiwan)		53 Piper kawakamii
71 (69)	Flowers bisexual; leaf base cuneate (mainland)		2 Piper chinense
+	Flowers unisexual, dioecious; leaf base rounded to cordate (Taiwan).		(72)
72 (71)	Leaf blade 6-10(-15) cm, broadly ovate to orbicular, base sometimes peltate in juvenile plants; male spikes 3.5-5 cm; female spikes 1-2.5 cm		52 Piper kwashoense
+	Leaf blade 9-13(-18) cm, ovate to elliptic, base never peltate; male spikes 5-8 cm; female spikes 2-3.5 cm		53 Piper kawakamii