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FOC | Family List | FOC Vol. 19 | Rubiaceae

65. Ophiorrhiza Linnaeus, Sp. Pl. 1: 150. 1753.

蛇根草属 she gen cao shu

Authors: Tao Chen & Charlotte M. Taylor

Hayataella Masamune; Mitreola Boehmer; Mungos Adanson.

Annual or perennial herbs or rarely subshrubs, unarmed, often fleshy or rather succulent, sometimes creeping. Raphides present. Leaves opposite, decussate, sometimes anisophyllous, without domatia; margins sometimes undulate to denticulate; stipules persistent or caducous, interpetiolar, entire or bifid to fimbriate, sometimes glandular. Inflorescences terminal and/or pseudoaxillary or rarely axillary (Ophiorrhiza oppositifolia), cymose to capitate, fasciculate, or paniculiform with axes often helicoid, few to many flowered, sessile to pedunculate, bracteate or bracts absent; bracts caducous to persistent, sometimes involucral. Flowers pedicellate to sessile, bisexual and distylous or monomorphic or occasionally cleistogamous. Calyx with ovary portion turbinate to obconical, usually strongly compressed, longitudinally often 5- or 10-ribbed; limb reduced or 5(or 6)-lobed, lobed essentially to base or rarely subtruncate (O. repandicalyx). Corolla white, yellow, orange, pink, purple, or brown, sometimes drying with markedly different color, usually notably clavate in bud, at anthesis salverform, tubular, or funnelform with tube often swollen to gibbous at base, outside often longitudinally ridged or winged, inside glabrous to variously pubescent; lobes 5(or 6), valvate in bud, smooth or occasionally ridged, winged, and/or with hornlike appendages near apex, apex sometimes adaxially rostrate. Stamens 5(or 6), inserted near throat to below middle of corolla tube, included or exserted; filaments reduced to well developed; anthers dorsifixed near middle or base. Ovary 2-celled, ovules numerous in each cell on axile placentas attached from middle to base of septum; stigmas 2, linear to subcapitate, included or exserted. Fruit capsular, obovoid to oblate, mitriform, or obcordate, strongly laterally compressed perpendicular to septum, sometimes with apical portion prolonged into a beak, loculicidally dehiscent across top and sometimes along sides, papery, with calyx limb persistent; seeds numerous, small, angled to rhomboid, areolate to alveolate.

About 200-300 species: tropical and subtropical Asia, Australia, New Guinea, Pacific islands; 70 species (49 endemic, one of unconfirmed occurrence) in China.

Ophiorrhiza is a notably species-rich, taxonomically complicated genus found in wet tropical forests of SE Asia (Darwin, Lyonia 1(2): 47-102. 1976); it has been little studied and is particularly poorly known in SE Asia (I. Schanzer, pers. comm.). Ophiorrhiza was studied for China by H. S. Lo (Bull. Bot. Res., Harbin 10(2): 1-82. 1990), who variously described 44 of the 68 Ophiorrhiza species recognized by Lo in FRPS (71(1): 110-174. 1999). The genus was studied in India by Deb and Mondal (Bull. Bot. Surv. India 39(1-4): 1-148. 1997), who recognized 47 species there. Darwin (loc. cit.) reported that the plants are notably variable in many vegetative features, many of which were shown by him not to be informative to separate species. H. S. Lo (loc. cit. 1999: 111) reported that the calyx and corolla lobes are occasionally 6, but this has not been noted by other authors nor seen on specimens studied; this may be an occasional variation found in one or two flowers on unusual plants, as in many Rubiaceae species. H. S. Lo also described the placentas as ascending from the septum base; however, Darwin (loc. cit.: 56) reported that in the Pacific Ophiorrhiza species the placenta is inserted in the middle of the septum in the flower and then often becomes displaced to near the base of the septum in fruit, whereas Puff et al. (Rubiaceae of Thailand, 190. 2005) gave the insertion of the placenta as being in the lower half of the septum. Puff et al. reported that the fruit function as splash cups for seed dispersal and observed that, regardless of the orientation of the flowers, the fruit become erect with enlarged and strengthened pedicels. Tan and Rao (Biotropica 13: 232-233. 1981) reported vivipary in a species of Ophiorrhiza growing in Singapore, with the seeds germinating within the capsules, pushing their cotyledons out through the suture where the valves open normally, and extending roots through the capsule locules and tissues; a similar condition may be found in Chinese Ophiorrhiza.

Darwin (loc. cit.: 47-102) noted that the presence of distyly in Ophiorrhiza has been controversial because the arrangement of the stigmas and anthers in the first dimorphic species found here differs from that of classic distyly, with strictly reciprocal sizes and positions. However, since then the recognition of distyly in Rubiaceae has expanded to include species that are at least a bit dimorphic and have intra-morph incompatibility, and Ophiorrhiza clearly belongs in this group and has been considered distylous by subsequent authors (Deb & Mondal, loc. cit.; Kudoh et al., J. Trop. Ecol. 17: 719-728. 2001; Schanzer, Thai Forest Bull. 33: 140-166. 2004). Also, some species with markedly dimorphic distylous flowers have subsequently been discovered (e.g., O. aureolina and O. rufopunctata). Deb and Mondal (loc. cit.: 15, f. 7) illustrated some of the variation in stamen and stigma position and internal corolla pubescence in distylous species of this genus. Homostyly has also been confirmed in the genus (Nakamura et al., J. Jap. Bot. 81: 113-120. 2006; J. Plant Res. 120: 501-509. 2007) and some species also appear to be autogamous (Nakamura et al., loc. cit. 2006). Schanzer (loc. cit.) noted that some species appear to vary in floral biology across their range, to include both homostylous and distylous populations; this situation has been found elsewhere in some distylous Rubiaceae, which have variation in expression of distyly (e.g., Faivre & McDade, Amer. J. Bot. 88: 841-853. 2001), though in those cases, the flowers resemble one of the distylous forms while Schanzer described a distinct floral form in the monomorphic plants. Schanzer also noted that some of these floral forms may be aberrant and cleistogamous rather than distylous. Nakamura et al. (loc. cit. 2007) studied two supposedly conspecific varieties of O. japonica in Japan, one homostylous and the other distylous, and concluded that the self-compatible homostylous plants differed in ploidy level, comprised a distinct lineage according to cpDNA sequences, and are better considered a separate species. They also noted that floral biology is not correlated with ploidy in general in Ophiorrhiza. Observations and documentation of the floral biology of Chinese Ophiorrhiza species are so far limited. Kudoh et al. (loc. cit.) presented a detailed analysis of the floral forms and possible genetic controls of these in O. napoensis in Guangxi, China. Also notable in the floral morphology of this genus is the apparent wide variation in corolla pubescence within a species, sometimes with the long-styled and short-styled flowers reportedly different (e.g., O. oppositiflora, floral forms similar but corolla pubescence variable, Deb & Mondal, loc. cit.: 88, f. 39; O. austroyunnanensis, pubescence apparently correlated with floral form, H. S. Lo, loc. cit. 1990: 31, f. 8).

Deb and Mondal (loc. cit.: 1) noted that the genus name alludes to the presumed healing properties of the root of these plants for snakebite and that Ophiorrhiza mungos and O. japonica are used for such in the Indian subcontinent. They also noted that species of this genus are used as medicine (for snakebites, stomach ulcers, skin eruptions, rheumatism, heart diseases), dye (red, for wool and hair), and food (the fruit), and list several references detailing their ethnobotany and medical chemistry.

The monotypic genus Hayataella, endemic to Taiwan, was recognized by several authors (particularly Taiwanese authors) as distinct from Ophiorrhiza, though it was synonymized by H. S. Lo (Bull. Bot. Res., Harbin 18: 276-277. 1998). Its morphology and molecular systematics were studied by Nakamura et al. (J. Plant Res. 119: 657-661. 2006), who concluded based on molecular data that the species belongs to a relatively derived clade of Ophiorrhiza and formally transferred the species, eliminating another of Taiwan’s few endemic genera.

No infrageneric classification has been recognized by recent authors (Darwin, loc. cit.: 47-102; Deb & Mondal, loc. cit.: 1-148).

H. S. Lo (loc. cit. 1990: 1-82) presented the definitive work on this genus in China. Most recently, Ophiorrhiza has been studied in China by Duan and Lin (Acta Phytotax. Sin. 45: 870-879. 2007), who synonymized several of Lo’s species. Their species circumscription is relatively broad compared to that of Lo, and a few of the species they synonymized are provisionally recognized here pending further study and a broader, consistent review of Ophiorrhiza in China.

Overall, the treatment of Ophiorrhiza here is primarily an organization of the published information, rather than a revisionary work. A few other species are keyed here even though their descriptions are incomplete; their placement is based in part on the key of H. S. Lo in FRPS (loc. cit. 1999: 112-117). In the FRPS treatment, H. S. Lo described in some detail the arrangement and degree of surface development and visibility of the tertiary venation on the abaxial leaf surface of many Ophiorrhiza species; however, this is incompletely described for the Chinese species, is variable within species, and was not used by Lo to distinguish species nor by other authors and, therefore, is not detailed here. Details of the anthers and stigmas are also incompletely described for Chinese Ophiorrhiza and mostly not used to separate species; the details available are summarized in the comments following the species description.

Among the names published in Ophiorrhiza by H. S. Lo (loc. cit. 1990), eight lacked an acceptable indication of type and were therefore not validly published under Art. 37 of the Vienna Code. In one case (O. chingii), two gatherings were cited but neither was indicated as the type, and in the other seven cases only one gathering was cited, which under Art. 37.3 is acceptable as indication of the type, but under Art. 37.6, on or after 1 January 1990, indication of the type must also include the word "typus" or "holotypus" or an equivalent in a modern language, and Lo did not include such words. All but one of the eight names were validated by S. Y. Jin and Y. L. Chen (Cat. Type Spec. Herb. China (Suppl.), 189-191. 1999) in each case by reference to Lo’s Latin description and by indication of a single gathering as the type (as "T."). The one remaining name, O. longicornis, is validated here.

1 Calyx lobes relatively well developed, longest ones 3.5 mm or longer (do not confuse bracts with calyx lobes)   (2)
+ Calyx lobes none (i.e., limb truncate) or longest lobes 3.4 mm or shorter (calyx lobe length unknown in O. rarior)   (7)
2 (1) Calyx lobes strongly unequal, more than 50% different in length, longer ones 3-6 mm and shorter ones 0.8-3 mm.   52 O. pingbienensis
+ Calyx lobes subequal, at most 50% different in length, 3.5-8 mm   (3)
3 (2) Corolla purple, tube 26-29 mm; stipules 1.5-2 mm.   64 O. sichuanensis
+ Corolla white or yellow, tube 13-19 mm (mature corolla unknown in O. hunanica); stipules 3-10 mm   (4)
4 (3) Stems glabrescent; calyx lobes linear; corolla externally with ciliate wings.   27 O. hunanica
+ Stems pilosulous or villous at least when young; calyx lobes linear, spatulate, or ovate; corolla externally smooth to ridged or with narrow, glabrous to pubescent wings   (5)
5 (4) Stipules ca. 10 mm, 2- or 3-lobed, lobes linear; bracts 10-20 mm; calyx lobes linear.   41 O. medogensis
+ Stipules 3-9 mm, triangular or 2-lobed; bracts 5-7 mm; calyx lobes ligulate, narrowly spatulate, ovate, or lanceolate   (6)
6 (5) Corolla with tube 13-14 mm and externally ridged or ribbed, lobes 2-2.5 mm; leaves in subequal pairs.   15 O. ensiformis
+ Corolla with tube 18-19 mm and externally ridged to winged, lobes ca. 4.5 mm; leaves in unequal pairs.   60 O. rufipilis
7 (1) Inflorescences axillary, paired at nodes below apex.   49 O. oppositiflora
+ Inflorescences terminal and/or pseudoaxillary, solitary at each node   (8)
8 (7) Stems densely lenticellate and moderately brown villous or -hirsute with multicellular trichomes when young.   56 O. rarior
+ Stems sparsely lenticellate to smooth, glabrous to densely pubescent with trichomes of various colors and forms when dry   (9)
9 (8) Corollas relatively small, tube 5.5 mm or shorter (corollas unknown in O. salicifolia)   (10)
+ Corollas larger, tubes more than 5.5 mm (corollas unknown in O. hainanensis and O. salicifolia)   (26)
10 (9) Leaves lanceolate-linear, 6 or more × as long as wide.   63 O. salicifolia
+ Leaves variously shaped, 3 × as long as wide or broader   (11)
11 (10) Corolla lobes with well-developed dorsal horns or appendages, these 1.5-2 mm   (12)
+ Corolla lobes dorsally smooth, ribbed, winged, or with thickenings or short hornlike protuberances, these up to 0.8 mm   (13)
12 (11) Inflorescences congested-cymose, branched to 1 or 2 orders; corolla pubescent in throat but glabrous below inside tube, pubescent externally.   6 O. cana
+ Inflorescences cymose to corymbose, branched to 3 or 4 orders; corolla pubescent below middle inside tube, glabrous externally.   35 O. longicornis
13 (11) Bracts and bracteoles well developed, lanceolate to spatulate or elliptic, 1-3 mm wide, partially to fully enclosing buds and flowers   (14)
+ Bracts and bracteoles reduced or linear to triangular, 0.1-0.8 mm wide, not enclosing buds or flowers   (15)
14 (13) Stipules ovate.   4 O. austroyunnanensis
+ Stipules triangular at base, quickly narrowed to a linear apex or linear lobes.   38 O. lurida
15 (13) Plants creeping or at least relatively small, at most 30 cm tall and most plants much shorter   (16)
+ Plants mostly weakly ascending to erect, generally rather robust, most plants 30 cm tall or taller   (18)
16 (15) Stipules 1-3 mm, caducous and often not visible; fruit 5-7 mm wide.   53 O. pumila
+ Stipules 4-10 mm, usually persisting on uppermost nodes; fruit 4-5 mm wide   (17)
17 (16) Leaves strigillose to glabrous adaxially.   24 O. hispidula
+ Leaves sparsely hispidulous adaxially.   62 O. rugosa
18 (15) Plants when dry covered with golden yellow pubescence, including on corollas.   3 O. aureolina
+ Plants glabrous or with pubescence drying white to brown, reddened, or clear   (19)
19 (18) Plants to 80-100 cm tall, with leaves 15-22 × 6-10 cm, with 11-19 pairs of secondary veins; calyx limb undulate to shallowly to moderately lobed   (20)
+ Plants to 70 cm tall, with leaves 2-15 × 1-6 cm, with (4 or)5-11(-19) pairs of secondary veins; calyx limb shallowly to deeply lobed   (21)
20 (19) Stipules deciduous after uppermost nodes, 4-8 mm; corolla tube 2.5-4 mm.   43 O. mungos
+ Stipules caducous, unknown; corolla tube ca. 5.5 mm.   57 O. repandicalyx
21 (19) Stipules 3-8 mm, deciduous after uppermost nodes; Taiwan.   29 O. kuroiwae
+ Stipules caducous and unknown, or persistent on uppermost nodes and 2-11 mm; mainland (including Hainan)   (22)
22 (21) Inflorescences well developed, cymose to paniculate; secondary leaf veins 7-19 pairs   (23)
+ Inflorescences somewhat reduced, congested-cymose to subcapitate; secondary leaf veins (4 or)5-7(-11) pairs   (24)
23 (22) Stipules caducous; corollas 3.5-5 mm.   43 O. mungos
+ Stipules mostly persistent; corollas 6-6.5 mm.   49 O. oppositiflora
24 (22) Corolla with pubescent ring inside tube, with lobes 1/4-1/3 as long as tube and spreading at anthesis.   62 O. rugosa
+ Corolla pubescent in throat and on upper part of tube but glabrous through most of tube, with lobes 1/3-1/2 as long as tube and spreading to strongly reflexed at anthesis   (25)
25 (24) Stipules triangular, 2-4 mm; corolla tube 2.5-4.5 mm, lobes spreading at anthesis.   38 O. lurida
+ Stipules subfiliform, ca. 6 mm; corolla tube 4.5-5 mm, lobes strongly reflexed at anthesis.   70 O. wui
26 (9) Leaves relatively narrow, more than 3 × as long as wide, often falcate, 4.5-11 × 0.6-2 cm   (27)
+ Leaves rather narrow to relatively broad, less than 3 × as long as wide, 0.5-25 × 0.3-10 cm   (28)
27 (26) Stems with 2 discrete lines of pubescence; bracteoles 1.5-3 mm.   34 O. lignosa
+ Stems glabrescent; bracteoles 4-5 mm.   63 O. salicifolia
28 (26) Corolla lobes dorsally with well-developed hornlike appendages 0.8-2 mm   (29)
+ Corolla lobes dorsally smooth, ridged, winged, and/or with dorsal thickenings on lobes, these sometimes hornlike but 0.7 mm or shorter   (32)
29 (28) Plants robust, to 2.5 m tall, leaves 10-20 × 4-7.5 cm, with 15 or 16 pairs of secondary veins.   44 O. mycetiifolia
+ Plants smaller to somewhat robust, to 1 m tall, leaves 2-17 × 2-4.5 cm, with 6-13 pairs of secondary veins   (30)
30 (29) Corolla tube 22-24 mm.   25 O. howii
+ Corolla tube 10.5-12 mm   (31)
31 (30) Leaves with secondary veins 8-12 pairs; calyx lobes 0.4-0.5 mm.   19 O. gracilis
+ Leaves with secondary veins 6 or 7 pairs; calyx lobes ca. 1.5 mm.   55 O. purpureonervis
32 (28) Plants creeping to procumbent, with most internodes prostrate and/or most nodes rooting   (33)
+ Plants erect to weak, with most internodes ascending and most nodes not rooting   (38)
33 (32) Corolla with tube 15-20 mm, lobes 5-6.5 mm   (34)
+ Corolla with tube 7-12 mm, lobes 2-5 mm   (35)
34 (33) Corolla externally with 5 pubescent lines.   42 O. mitchelloides
+ Corolla externally glabrous or uniformly pubescent.   33 O. liangkwangensis
35 (33) Corolla lobes ca. 2 mm; stems glabrescent or pilosulous in lines.   30 O. kwangsiensis
+ Corolla lobes 2.2-5 mm; stems generally uniformly villous, hirtellous, or pilosulous   (36)
36 (35) Bracts well developed, 3.5-6 mm; leaf base regularly cordate.   11 O. cordata
+ Bracts reduced, 1-2 mm; leaf base obtuse, truncate, or sometimes cordulate   (37)
37 (36) Corolla lobes 2.5-3 mm.   14 O. dulongensis
+ Corolla lobes 4-5 mm.   26 O. huanjiangensis
38 (32) Corolla with tube 18-27 mm   (39)
+ Corolla with tube less than 18 mm (corolla unknown in O. hainanensis)   (53)
39 (38) Bracts and bracteoles well developed, enclosing buds and at least partially flowers, ligulate, lanceolate, ovate, elliptic, or elliptic-oblong, 10-18 mm   (40)
+ Bracts and bracteoles reduced to developed, not enclosing or covering buds or flowers, linear, narrowly triangular, or narrowly lanceolate, 5.5 mm or shorter   (43)
40 (39) Stems villous; corolla funnelform at least in upper part   (41)
+ Stems glabrous; corolla salverform to funnelform   (42)
41 (40) Corolla lobes not evidently veined, ca. 5 mm.   20 O. grandibracteolata
+ Corolla lobes pinnately veined, 6-8 mm.   58 O. rhodoneura
42 (40) Corolla funnelform, tube villous inside above middle.   16 O. fangdingii
+ Corolla salverform to funnelform, tube glabrous inside.   46 O. napoensis
43 (39) Stems villous, villosulous, hirsute, hispidulous, strigose, strigillose, or pilosulous   (44)
+ Stems glabrous to puberulent   (48)
44 (43) Calyx lobes 0.4-1.5 mm; flowers several to many   (45)
+ Calyx lobes 1-3 mm; flowers 1-5   (46)
45 (44) Peduncle 1.5-3.5 cm; corolla tube 18-20 mm, pubescent inside.   9 O. chinensis
+ Peduncle 1-1.5 cm; corolla tube 23-27 mm, glabrous inside.   68 O. wallichii
46 (44) Corolla tube 22-26 mm; leaves without gland dots abaxially.   54 O. purpurascens
+ Corolla tube 18-22 mm; leaves with or without gland dots abaxially   (47)
47 (46) Leaves without or usually with reddish gland dots abaxially; fruit 5-6 × ca. 11 mm.   61 O. rufopunctata
+ Leaves without gland dots abaxially; fruit ca. 3 × 8 mm.   69 O. wenshanensis
48 (43) Leaves broadly ovate to broadly elliptic, abaxially with numerous small scales.   12 O. crassifolia
+ Leaves elliptic, lanceolate, ovate, ovate-oblong, or elliptic-oblong, glabrous to variously pubescent but without scales   (49)
49 (48) Stipules generally persistent at least on uppermost nodes, 6-8 mm.   39 O. macrantha
+ Stipules generally caducous, unknown or perhaps reduced   (50)
50 (49) Calyx lobes unequal, 0.7-2 mm.   45 O. nandanica
+ Calyx lobes subequal, 0.4-1.5 mm   (51)
51 (50) Fruit 14-15 mm wide.   68 O. wallichii
+ Fruit 8-11 mm wide   (52)
52 (51) Leaves 3.5-15 cm, with 9 or 10 pairs of secondary veins; corolla white to pale purple-red; widespread.   9 O. chinensis
+ Leaves 9-15 cm, with 10-14 pairs of secondary veins; corolla red to purplish red; Xizang, Yunnan.   67 O. umbricola
53 (38) Stipules generally well developed, 3-16 mm, and persistent at least on uppermost nodes of flowering stems   (54)
+ Stipules caducous and not seen, or 3 mm or shorter   (66)
54 (53) Calyx lobes rather well developed, 1.5-2.5 mm with at least some longer than 1.5 mm   (55)
+ Calyx lobes smaller, 0.5-1.5 mm with at least some shorter than 1.5 mm   (56)
55 (54) Leaves larger, 6.5-22 × 2.5-10 cm; bracts 7-9 mm.   40 O. macrodonta
+ Leaves smaller, 1-4 × 0.6-2.5 cm; bracts reduced, to ca. 1 mm.   14 O. dulongensis
56 (54) Bracts and bracteoles reduced, to 3 mm, mostly or all deciduous before anthesis   (57)
+ Bracts and bracteoles generally well developed, 3-12 mm, generally persistent at least through anthesis   (59)
57 (56) Leaves smaller, 2-11 × 1-5 cm; corollas pubescent inside, glabrous to pubescent outside.   62 O. rugosa
+ Leaves larger, 6.5-25 × 2-10 cm; corollas glabrous inside and puberulent to glabrous outside   (58)
58 (57) Corollas yellow to pale yellow; peduncles in flower 3-10 cm (these later elongating in fruit).   48 O. ochroleuca
+ Corollas purplish red; peduncles in flower 2.5-5 cm (these later elongating in fruit).   59 O. rosea
59 (56) Leaves in markedly unequal pairs, larger ones 1.5-3 × as long as shorter   (60)
+ Leaves in subequal pairs   (61)
60 (59) Corolla pink or purplish red, tube ca. 11 mm, lobes ca. 1.5 mm and dorsally with short hornlike appendage.   5 O. brevidentata
+ Corolla white, tube ca. 9 mm, lobes 2-3 mm and dorsally narrowly winged.   47 O. nutans
61 (59) Leaves larger, at least some 10-16 × 4-6.5 cm; peduncles in flower 1-8 cm   (62)
+ Leaves smaller, 0.8-13 × 0.5-4 cm; peduncles in flower 0.5-6 cm   (64)
62 (61) Peduncle in flower 1.5-2 cm; bracts 3-4 mm; corolla pubescent inside.   23 O. hispida
+ Peduncle in flower 1-8 cm; bracts 6-12 mm; corolla glabrous inside   (63)
63 (62) Calyx with hypanthium portion 1-1.5 mm, lobes 1-1.2 mm.   17 O. fasciculata
+ Calyx with hypanthium portion ca. 3 mm, lobes ca. 0.5 mm.   48 O. ochroleuca
64 (61) Peduncle in flower 1-3 cm; bracts 3-6.5 mm; leaves obtuse at apex.   50 O. pauciflora
+ Peduncle in flower 0.5-6 cm; bracts 5-10 mm; leaves acute to cuspidate or acuminate at apex   (65)
65 (64) Plants viscid puberulent, trichomes unicellular and not drying particularly dark; leaves with secondary veins 15-17 pairs; Hainan.   21 O. hainanensis
+ Plants villous, trichomes multicellular, drying reddish brown, not glandular; leaves with secondary veins 9-15 pairs; mainland.   47 O. nutans
66 (53) Calyx and fruit densely tuberculate with peglike, flat- to round-topped protuberances; Taiwan.   22 O. hayatana
+ Calyx and fruit smooth, glabrous to pubescent with slender trichomes   (67)
67 (66) Plants drying purple throughout (on live plants, see old and dying tissues)   (68)
+ Plants drying green, brown, yellowed, gray, blackened, or with parts flushed purple   (69)
68 (67) Corolla with tube 9-14 mm; leaves 4-11 × 0.7-3.5 cm; bracts 1-6 mm.   28 O. japonica
+ Corolla with tube 7-10 mm; leaves 5-20 × 2.5-8 cm, at least some longer than measurements in alternate lead; bracts 6-9 mm.   66 O. succirubra
69 (67) Stems (but not necessarily inflorescences) villous to hispid with well-developed spreading trichomes   (70)
+ Stems glabrous or strigillose, puberulent, hispidulous, and/or villosulous with short, appressed to spreading trichomes   (71)
70 (69) Calyx lobes ca. 0.5 mm; corolla pale purple or white, with tube 10-12 mm and lobes ca. 1 mm.   23 O. hispida
+ Calyx lobes 1-1.3 mm; corolla yellowish white or tinged with purple, with tube ca. 16 mm and lobes 5-5.5 mm.   36 O. longipes
71 (69) Leaves relatively broad, less than 2 × as long as wide, 11-16 × 5.5-10 cm.   8 O. carnosicaulis
+ Leaves moderately broad to rather narrow, 2 or more × as long as wide, 1.5-20 × 0.7-7 cm   (72)
72 (71) Leaves with secondary veins 13-23 pairs, at least some leaves with more than 13 pairs   (73)
+ Leaves with secondary veins 4-15 pairs, at least some leaves with fewer than 13 pairs   (74)
73 (72) Calyx puberulent; corolla lobes 1.8-4 mm, dorsally winged.   7 O. cantonensis
+ Calyx hispidulous; corolla lobes ca. 1.5 mm, with short hornlike appendage.   13 O. densa
74 (72) Bracteoles well developed, 7-12 mm.   2 O. alatiflora
+ Bracteoles none, reduced, or moderately well developed, 6 mm or shorter   (75)
75 (74) Bracts and bracteoles reduced or caducous, not or hardly visible   (76)
+ Bracts and bracteoles developed, evident, persisting at least with flowers, bracteoles 1-6 mm   (81)
76 (75) Leaves in unequal pairs, with secondary veins prominent adaxially.   37 O. luchuanensis
+ Leaves in subequal pairs, with secondary veins flat to impressed adaxially   (77)
77 (76) Leaves with 5 or 6 pairs of secondary veins; stems puberulent to glabrescent.   31 O. laevifolia
+ Leaves with 7-15 pairs of secondary veins; stems glabrous, puberulent, or hispidulous   (78)
78 (77) Leaves rounded-obtuse at apex.   65 O. subrubescens
+ Leaves acute or acuminate at apex   (79)
79 (78) Stems hispidulous.   49 O. oppositiflora
+ Stems glabrous or puberulent   (80)
80 (79) Corolla tube ca. 12 mm.   1 O. alata
+ Corolla tube 4-8 mm.   49 O. oppositiflora
81 (75) Leaves mostly or all in markedly unequal pairs, longer ones 2-3 or more × as long as shorter   (82)
+ Leaves in subequal pairs or some in unequal pairs, longer ones at most 1.5 × as long as shorter   (83)
82 (81) Leaf pairs with longer ones 3 or more × as long as shorter; inflorescences pilosulous or puberulent with slender trichomes.   10 O. chingii
+ Leaf pairs with longer ones 2-2.5 × as long as shorter; inflorescences mealy puberulent.   32 O. laoshanica
83 (81) Stems and leaves abaxially mealy puberulent; corolla lobes dorsally with short hornlike appendages.   18 O. filibracteolata
+ Stems and leaves abaxially glabrous to variously pubescent with slender trichomes; corolla lobes dorsally smooth to winged and/or with short hornlike appendages   (84)
84 (83) Leaves elliptic to elliptic-oblong, 6-20 × 1.5-7 cm, at least some leaves longer than measurements in alternate lead, with 9-15 pairs of secondary veins, generally becoming yellowed or brownish yellow when dry.   7 O. cantonensis
+ Leaves elliptic to lanceolate or ovate, 1-11 × 0.7-4 cm, at least some leaves smaller than measurements in alternate lead, with 4-13 pairs of secondary veins, generally drying with green, gray, blackish, or purplish cast   (85)
85 (84) Stigmas ovate to elliptic or lanceolate; widespread, common.   28 O. japonica
+ Stigmas linear; known only from Yunnan, rare.   51 O. petrophila

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