1	Valves of fruit not internally septate		(2)
+	Valves of fruit internally septate, or if 1-seeded then wall convex at both ends of valve		(19)
2 (1)	Leaves simple		(3)
+	Leaves imparipinnate		(4)
3 (2)	Flowers pink; standard retuse; ovary glabrous.		17 O. simplicifolia
+	Flowers white; standard broadly rounded; ovary yellow pubescent.		18 O. boluoensis
4 (2)	Legumes densely appressed pubescent		(5)
+	Legumes glabrous or sparsely pubescent, sometimes only at margin		(10)
5 (4)	Legumes indehiscent or tardily dehiscent; hilum 15-18 mm, over 1/2 circumference of seed.		1 O. balansae
+	Legumes dehiscent; hilum less than 4 mm		(6)
6 (5)	Hilum 3-4 mm, seed light red; legumes slightly convex; branchlets and leaves abaxially with short hairs, glabrous at maturity; leaves widest at middle.		13 O. nanningensis
+	Hilum small, 1-1.5 mm, seed dark brown or chestnut-brown; legumes turgid or somewhat turgid; branchlets and leaves abaxially densely appressed pubescent; leaves often widest above middle		(7)
7 (6)	Leaflet apex caudate, narrow, length ca. 4 × width.		4 O. inflata
+	Leaflet apex acute to abruptly mucronate, length less than 3 × width		(8)
8 (7)	Legumes with stipe; branchlets and leaves abaxially densely appressed yellow-brown tomentose.		5 O. sericeolucida
+	Stipe absent; branchlets and leaves abaxially sparsely to densely appressed yellow tomentose, or white or brown woolly		(9)
9 (8)	Leaflets 5-7, densely appressed white woolly, becoming gray woolly.		2 O. pachycarpa
+	Leaflets 5-9, glabrous adaxially, sparsely to densely yellow-brown tomentose abaxially.		3 O. merrilliana
10 (4)	Seeds large, more than 2 cm, hilum inconspicuous		(11)
+	Seeds smaller, less than 18 mm, hilum conspicuous, large or small		(12)
11 (10)	Legumes compressed, brownish outside, ivory inside; seed red-brown; branchlets densely rusty brown pubescent.		7 O. fordiana
+	Legumes swollen, brownish to black outside, brownish inside; seed chestnut-brown; branchlets glabrous or finely white pilose.		6 O. longipes
12 (10)	Seeds 14-18 mm; legumes yellowish brown		(13)
+	Seeds less than 14 mm; legumes black or light blackish brown		(15)
13 (12)	Hilum small, less than 3 mm; leaflets 3-5; branchlets brownish pilose.		16 O. napoensis
+	Hilum 9-10 mm; leaflets 5-7; branchlets glabrous		(14)
14 (13)	Legumes compressed, suborbicular, valves leathery, mesocarp absent; leaflets ovate.		14 O. hosiei
+	Legumes fleshy, elliptic, protuberant, valves woody, mesocarp conspicuous; leaflets oblong.		15 O. elliptica
15 (12)	Legumes oblique-elliptic, obovate, or oblong-elliptic, length greater than width; seeds 1-3		(16)
+	Legumes suborbicular, length equaling width; seed 1, rarely 2		(17)
16 (15)	Valves thickly leathery; branchlets densely appressed rusty brown tomentose; leaves appressed pubescent abaxially.		12 O. yunnanensis
+	Valves thinly leathery; branchlets glabrous or glabrescent; leaves glabrous abaxially.		11 O. pingbianensis
17 (15)	Legumes apiculate at apex, mucro 4-6 mm, curved, stipe 5-8 mm; both petiole and rachis glabrous.		8 O. apiculata
+	Legumes apiculate at apex, mucro less than 4 mm, stipe less than 4 mm; petiole and rachis pubescent		(18)
18 (17)	Legumes inequilateral; valves thickly leathery, sparsely pubescent, more conspicuous at margin; leaflets oblong-obovate, thickly leathery, widest above middle, apex acute; rachis prolonged 5-8 mm below terminal leaflet.		10 O. howii
+	Legumes equilateral; valves thinly leathery, sparsely pubescent at margin when young, becoming glabrescent; leaflets oblong, leathery, widest below (rarely above) middle, apex acuminate; rachis prolonged more than 10 mm below terminal leaflet.		9 O. semicastrata
19 (1)	Legumes very fleshy, valves 6-10 mm thick, often stained red internally; seeds large, 2.5-3 cm, elliptic, red-brown.		19 O. hekouensis
+	Legumes compressed or slightly fleshy, valves thinly woody or leathery, less than 5 mm thick, not stained red internally; seeds small, less than 2 cm		(20)
20 (19)	Branchlets, petiole, and rachis densely appressed brownish or rusty brown tomentose		(21)
+	Branchlets, petiole, and rachis glabrous or sparsely appressed pubescent, old branches sparsely glabrous		(26)
21 (20)	Legumes densely appressed fulvous sericeous.		26 O. xylocarpa
+	Legumes glabrous or only basally pubescent at maturity		(22)
22 (21)	Valves thinly woody, swollen around seed; leaflets leathery, glossy, pale green when dry; leaf scar flat to concave		(23)
+	Valves thickly woody, flattened or slightly convex; leaflets papery or rigidly papery, dull, dark green when dry; leaf scar protruding		(24)
23 (22)	Legumes 4-6 cm; seeds 2-4; calyx ca. 7 mm; leaflets 13-19, sparsely appressed pubescent abaxially; branchlets dark rusty brown pubescent.		24 O. ferruginea
+	Legumes 5-12 cm; seeds 4-8; calyx 12-14 mm; leaflets fewer than above, densely appressed tomentose abaxially; branchlets pale fulvous pubescent.		22 O. henryi
24 (22)	Leaflets (14-)17-23, both surfaces densely appressed fulvous velvety, more so abaxially.		34 O. saxatilis
+	Leaflets often fewer than 17, rarely more, glabrous, rarely sparsely appressed pubescent		(25)
25 (24)	Leaves larger, often more than 4.5 cm, apex acuminate, lateral veins impressed adaxially when dried.		32 O. olivacea
+	Leaves smaller, often less than 4.5 cm, apex obtuse, lateral veins slightly raised when dried.		33 O. microphylla
26 (20)	Leaflets 11-19, abaxially pale when dried		(27)
+	Leaflets 3-9(-11), not pale abaxially when dried		(28)
27 (26)	Leaflets 15-19, widest above middle, apex long acuminate or caudate, rachis convex between pair of leaflets.		23 O. pachyptera
+	Leaflets 11-13, widest at middle or slightly lower, apex obtuse, not long acuminate, rachis not convex.		25 O. purpureiflora
28 (26)	Ovary and legume glabrous		(29)
+	Ovary completely pubescent or at least on margin; legumes ± pubescent, rarely glabrous		(31)
29 (28)	Racemes axillary; leaflets 7-9(-11), apex caudate; valves fulvous when dried; seeds 1.1-1.8 cm, striate.		27 O. striata
+	Panicles terminal; leaflets 5-7, apex not caudate; valves blackish when dried; seeds 1-1.5 cm, not striate		(30)
30 (29)	Leaflets obovate or obovate-elliptic, apex obtuse, emarginate; calyx pubescent along outer margin and inside; standard apex rounded.		20 O. emarginata
+	Leaflets ovate or elliptic-lanceolate, apex acuminate; calyx pubescent inside and out; standard apex retuse.		21 O. glaberrima
31 (28)	Legumes cylindric or slightly compressed, orange-red at maturity and brownish when dry.		28 O. pinnata
+	Legumes compressed, brownish at maturity and blackish brown when dry		(32)
32 (31)	Leaflets obovate or oblanceolate, apex obtuse or emarginate; legumes 2-4.5 cm		(33)
+	Leaflets elliptic or oblong, apex acute; legumes 3-10 cm		(34)
33 (32)	Young branchlets sparsely fulvous velvety; leaflets 7-9, often oblanceolate, lateral veins 4-6 pairs.		29 O. indurata
+	Young branchlets densely appressed fulvous pubescent; leaflets (5-)7, obovate, lateral veins 5-8 pairs.		30 O. eugeniifolia
34 (32)	Legumes somewhat fleshy, swollen, densely appressed short grayish brown pubescent; leaflets 5, often elliptic, apex acute.		31 O. pubescens
+	Legumes slightly compressed; leaflets 7-23, oblong, apex acuminate, caudate, or acute		(35)
35 (34)	Rachis prolonged more than 1 cm below terminal leaflet; legumes more than 4 cm; plants of mainland China.		37 O. nuda
+	Rachis prolonged less than 1 cm below terminal leaflet; legumes less than 3 cm; plants restricted to Taiwan		(36)
36 (35)	Leaflets 3-5(-7), apex acute to acuminate, margin entire, not sinuous; flowers white; seeds globose.		35 O. formosana
+	Leaflets (5-)7(-9), apex acute to obtuse, slightly retuse, margin entire, often sinuous; flowers reddish purple; seeds angular.		36 O. hengchuniana