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FOC | Family List | FOC Vol. 19 | Rubiaceae

79. Rubia Linnaeus, Sp. Pl. 1: 109. 1753.

茜草属 qian cao shu

Authors: Tao Chen & Friedrich Ehrendorfer

Shrubs, subshrubs, or perennial herbs, not rarely clambering or climbing vines or rarely lianas, unarmed; stems often prickly and/or longitudinally ribbed or winged. Raphides present. Leaves opposite and with interpetiolar, triangular or ovate, persistent to caducous (Rubia siamensis) or reduced (R. tibetica) stipules or with leaflike stipules in whorls of 4, 6, to many in middle stem regions; domatia none; main veins single or 3-5(or more) and then palmate, secondary veins lateral. Inflorescences thyrsoid, with terminal and/or axillary cymes, usually paniculiform and often expanding from new axes developing with age; individual cymes few to many flowered, pedunculate, bracteate. Flowers pedicellate or sessile, rather small, usually bisexual and monomorphic, rarely polygamo-dioecious (R. cordifolia). Ovary inferior (hypanthium), ellipsoid, subglobose, 2-celled, ovules 1 in each cell, erect, axile. Calyx limb reduced and obsolete. Corolla white to cream, yellow, greenish or red to purplish, often turning black when dried, mostly rotate, but rarely also campanulate to funnel-shaped, inside glabrous or infrequently papillose; lobes predominantly 5 (rarely also less or more), valvate in bud, often long acuminate. Stamens usually 5, inserted at corolla base (or tube), exserted; filaments developed to reduced; anthers dorsifixed. Stigmas 2-lobed, included or exserted. Fruit developing into 2 separate or (by reduction) into only 1 subglobose, baccate, berrylike mericarp with fleshy meso- and endocarp, dark red, purple, black, or infrequently orange (R. cordifolia), glabrous or somewhat hairy; seeds ("pyrenes") 2, ellipsoid, subglobose, or plano-convex, with membranous testa; endosperm corneous; embryo subincurved; cotyledons leaflike; radicle prolonged, basiscopic.

About 80 species: extending from tropical and temperate Asia to Japan and Indonesia, through the Himalaya to SW Asia, E to S Africa, through the Mediterranean to W Europe, Macaronesia, and the Azores; locally introduced and persisting from cultivation in Mexico, Chile, and elsewhere; 38 species (20 endemic) in China.

As already mentioned in the present volume under Galium, Rubia is the type genus of the family, the tribe Rubieae, and the subtribe Rubiinae. As an Old World clade, Rubia is related to the Mesoamerican genus Didymaea and occupies a relative basal position within Rubiinae: its 5-lobed corollas, fleshy fruit, and always perennial growth form apparently are plesiomorphic features. This and its clear separation from the somewhat more apomorphic Sherardia-Asperula-Galium group is well documented by DNA data (Natali et al., Opera Bot. Belg. 7: 193-203. 1996; Soza & Olmstead, Taxon 59: 755-771. 2010). Rubia is keyed out from among the other Chinese taxa of Rubieae under Galium on p. 107. Its best differential characters are the dominantly 5-merous flowers combined with baccate, berrylike mericarps. The latter also occur independently among New World taxa of Galium (and Relbunium).

Among the Rubieae tribe Rubia (after Galium and Asperula in their present circumscription) is the third largest and obviously monophyletic genus. Nearly half of its recognized species occur in China. Because of excessive variability, the occurrence of hybridization and polyploidy as well as the lack of detailed studies (particularly on material in the major herbaria of China and elsewhere), our knowledge of Rubia is limited and the present treatment of the genus still quite provisional.

More recent taxonomic surveys of Rubia are available for the former Soviet Union (Pojarkova, Fl. URSS 23: 382-417. 1958), India (Deb & Malick, Bull. Bot. Surv. India 10(1): 1-16. 1968), Iran (Ehrendorfer et al., Fl. Iranica 176: 48-72. 2005), Bhutan (Long, Edinburgh J. Bot. 53: 108-110. 1996; Long, Fl. Bhutan 2(2): 823-825. 1999), and Taiwan (T. Y. A. Yang, Fl. Taiwan, ed. 2, 4: 321-324. 1998). Particularly in the first of these contributions, but also in the following two, the infrageneric taxonomy of Rubia is briefly considered. The majority of the Chinese species are characterized by 3-5(-11) palmate veins in their relatively broad leaves. These taxa correspond to R. sect. Oligoneura Pojarkova (= R. [unranked] Cordifoliae Candolle; R. sect. Cordifoliae (Candolle) K. Schumann ex Deb & Malick). Within this section Pojarkova (loc. cit.) has recognized two series: one predominantly climbing vines with long leaf petioles as R. ser. Cordifoliae (Candolle) Pojarkova (with 16 species in China; see under R. cordifolia), the other mostly erect perennial herbs with very short leaf petioles as R. ser. Chinenses (with three species in China; see under R. chinensis). The latter is close to the informal R. mandersii group, where the leaves are sessile (three species in China; see under R. mandersii). Finally, there are two species groups with vines. One is the R. sikkimensis group with sessile leaves and leaflike stipules (two Chinese species; see under R. tenuis), in the other, the R. siamensis group, typical (not leaflike) interpetiolar stipules appear between the opposite leaves (four species in China; see under R. siamensis).

The remaining ten Chinese species have leaves with only 1(-3) main vein(s) and predominantly pinnate vein branching. In the present treatment this refers to the species Rubia chitralensis, R. deserticola, R. dolichophylla, R. rezniczenkoana, R. schugnanica, R. tibetica, and R. tinctorum, here provisionally accommodated in R. sect. Rubia s.l. (including R. sect. Meganthera Pojarkova (= R. sect. Rubia s.s.), R. sect. Campylanthera Pojarkova, and R. sect. Chonanthe Pojarkova). The placement of the E Asiatic species R. haematantha (the R. haematantha group; see there) as well as R. pseudogalium and R. truppeliana (the R. truppeliana group; see there) is doubtful; they may belong to R. sect. Oligoneura in spite of their very narrow leaves and only 1 main vein. The more detailed infrageneric subdivisions of Rubia by Pojarkova listed above have been based on size and form of anthers and other flower details and are in need of more general and detailed study.

Relevant characters for the separation of Rubia taxa on the species level are growth habit, indumentum, number, shape and consistency of leaves and stipules, presence or absence of petioles, inflorescence structures, color and morphology of corollas from rotate to funnel-shaped, fruit color, etc. Particularly, leaf characters often vary excessively under different environmental and developmental conditions (e.g., in more widespread taxa as Rubia cordifolia and its allies; see further comments there). These facts are difficult to evaluate, at least on dried specimens.

The ground-up rhizomes and roots of Rubia tinctorum, the type species of the genus, have long been the source of important red textile dyes (madder red, alizarin, rose madder, alizarin crimson). This use was of course much more important before the invention of aniline dyes (e.g., madder colored the red coats of the 18th-century British army). Nevertheless, R. tinctorum is still widely cultivated at a local scale and used, in particular, to color wool for handmade oriental rugs in C and SW Asia (Murphy, Root of Wild Madder, 1-297. 2005) but also in fine art painting. The worldwide occurrence, cultivation, chemistry, and cultural role of this species was discussed in detail by Chenciner (Madder Red. 2000). The stems of R. manjith are also used to produce a red dye (fide Long, loc. cit. 1999).

The key here generally follows that of H. S. Lo (in FRPS 71(2): 287-290. 1999), with the measurements updated from the descriptions and species added as appropriate.

1 Leaves with only 1 evident midvein; lateral veins pinnate, when palmate weak and obscure   (2)
+ Leaves with 3-11 evident principal and palmate veins (including midrib), arising from at or near base   (11)
2 (1) Leaves linear to narrowly lanceolate or oblong, mostly 3.5-30 × as long as wide   (3)
+ Leaves broadly (ob)lanceolate, lanceolate-oblong, ligulate, elliptic, elliptic-oblong, lanceolate-ovate, ovate, or broadly ovate, mostly 1-3.5 × as long as wide   (7)
3 (2) Leaves with well-developed petioles; plants of forests   (4)
+ Leaves without distinct petioles, sessile to subsessile; plants of open habitats   (5)
4 (3) Leaves in whorls of up to 6-8, with petioles 6-35 mm; peduncles 10-40 mm; corolla lobes ca. 2 mm; Shandong.   36 R. truppeliana
+ Leaves in whorls of never more than 4, with petioles 3-6 mm; peduncles 3-6 mm; corolla lobes 1.2-1.5 mm; Yunnan.   24 R. pseudogalium
5 (3) Corolla dark red or perhaps sometimes white; leaves 6-8 per whorl, narrowly linear, less than 1 mm wide, midvein without evident lateral veins.   12 R. haematantha
+ Corolla yellow or white; leaves 4-6 per whorl, linear-lanceolate to lanceolate-oblong, wider than 1 mm   (6)
6 (5) Leaves 5-14 mm wide, midvein with pinnate lateral veins; stems with aculeolate angles; inflorescence cymes terminal and distributed along lower stem nodes; corolla lobes ca. 2 mm.   8 R. dolichophylla
+ Leaves 20-50 mm wide, lateral veins not evident; stems smooth; inflorescence cymes clustered near stem apices; corolla lobes 2.3-2.7 mm.   28 R. schugnanica
7 (2) Corolla lobes with apex aristate, arista 0.5-0.8 mm; leaves 4-6 in a whorl, lanceolate or elliptic-oblong, drying firmly leathery.   7 R. deserticola
+ Corolla lobes obtuse, acute, or acuminate to mucronate, with arista up to 0.4 mm; leaves lanceolate to broadly ovate, drying papery to leathery   (8)
8 (7) Larger leaves longer and wider than 3 × 1.5 cm, dried papery to subleathery   (9)
+ Leaves 0.5-3 × 0.2-1.5 cm, dried leathery   (10)
9 (8) Leaves dried papery; corolla limb 6-7.5 mm in diam.; anthers ca. 0.4 mm.   4 R. chitralensis
+ Leaves dried papery to subleathery; corolla limb 3-4.5 mm in diam.; anthers ca. 0.6 mm.   34 R. tinctorum
10 (8) Leaves and leaflike stipules similar, mostly up to 6 per whorl; lower nodes of older stems not sheathed with old leaf bases; corolla yellow, lobes often 4, obtuse with short incurved cusp.   26 R. rezniczenkoana
+ Leaves 2 with 2 smaller leaflike interpetiolar stipules in whorls of 4; lower nodes of older stems shortly sheathed with membranous bases of old leaves; corolla whitish, lobes usually 5, acuminate.   33 R. tibetica
11 (1) Leaves opposite, with evident interpetiolar stipules; plants of moist forests   (12)
+ Leaves and leaflike stipules similar, in whorls of 4-12; plants of various habitats   (16)
12 (11) Leaves tuberculate-hispidulous; stipules ± leaflike but smaller than true leaves.   6 R. crassipes
+ Leaves glabrous, scabrous, or ± hairy; stipules ovate to triangular, very different from true leaves   (13)
13 (12) Leaf margins entire and smooth, petioles 0.3-2.5 cm; inflorescence axes slender and filiform.   11 R. filiformis
+ Leaf margins aculeolate, petioles (1-)2-4(-8) cm; inflorescence axes stout   (14)
14 (13) Ovary and fruit densely hairy.   10 R. falciformis
+ Ovary and fruit glabrous   (15)
15 (14) Stipules large, ovate, acuminate, (5-)12-35(-60) × (3-)8-25(-40) mm; dried leaves light green and ± ferruginous, particularly below and on main veins.   15 R. magna
+ Stipules small, triangular, 3-5(-7) × 2-3 mm; dried leaves dark green.   30 R. siamensis
16 (11) Erect herbs, if ± climbing vines then leaves (sub)sessile; leaves and leaflike stipules 4 or sometimes 6 per whorl   (17)
+ Vines or lianas, climbing to sprawling; leaves petiolate, petioles 0.1-12 cm   (29)
17 (16) Leaves markedly cordate at base   (18)
+ Leaves cuneate, obtuse, truncate, rounded, or shallowly cordulate at base   (20)
18 (17) Older stems broadly 4-winged.   25 R. pterygocaulis
+ Older stems quadrangular to narrowly 4-angled   (19)
19 (18) Stem angles retrorsely aculeate; mountains of Taiwan.   2 R. argyi
+ Stem angles smooth; Sichuan.   13 R. latipetala
20 (17) Leaves sessile or subsessile (if flowers 4-merous then see Galium)   (21)
+ Leaves petiolate, petioles 0.3-9 cm   (25)
21 (20) Principal leaf veins 7-11; stems and leaves strongly hairy; fused basal part of corolla only 0.2-0.3 mm, lobes 1-1.2 mm.   23 R. polyphlebia
+ Principal leaves veins 3 or 5; stems and leaves ± glabrescent to glabrous, scabrous; fused basal part of corolla 0.5-0.6 mm   (22)
22 (21) Slender vines; leaves drying papery; flowers ca. 3 mm in diam.   32 R. tenuis
+ Erect to spreading herbs; leaves drying mostly ± leathery; flowers 3-5 mm in diam   (23)
23 (22) Stems 8-ribbed; leaves lanceolate to lanceolate-elliptic, 4-7 cm.   9 R. edgeworthii
+ Stems 4-angled; leaves broadly elliptic, linear-lanceolate, ovate, obovate, or elliptic-oblong, 1-5 cm   (24)
24 (23) Stems and leaves glabrous to scabrous, latter drying papery; principal main veins 5; corolla ca. 5 mm in diam.   16 R. mandersii
+ Stems and leaves often ± hairy or scabrous, latter drying ± papery; principal veins 3-5; corolla ca. 3 mm in diam.   38 R. yunnanensis
25 (20) Stems clearly retrorsely aculeolate   (26)
+ Stems smooth to sparsely scaberulous   (27)
26 (25) Leaves suborbicular to ovate, length/breadth index 1-1.8, dried papery.   2 R. argyi
+ Leaves lanceolate to ovate, length/breadth index 2-3, dried papery to subleathery.   22 R. podantha
27 (25) Leaves ± broadly elliptic, principal veins 5-7, dried thinly papery; fused part of corolla 0.2-0.6 mm.   3 R. chinensis
+ Leaves broadly lanceolate to ± broadly ovate, principal veins 3-5, dried papery to subleathery; fused part of corolla 0.8-2 mm   (28)
28 (27) Leaves ± broadly ovate, length/breadth index 1.2-1.5, base cordulate to cordate, dried papery, principal veins 3-5; fused part of corolla 1.5-2 mm.   13 R. latipetala
+ Leaves broadly lanceolate to ovate, length/breadth index 1.5-2.5, base obtuse, rounded, or cordulate, dried thickly papery to subleathery, principal veins often impressed; fused part of corolla 0.8-1 mm.   29 R. schumanniana
29 (16) Fruit, stems, and leaves hirsute, strigillose, hirtellous, or villosulous.   35 R. trichocarpa
+ Fruit glabrous, stems and leaves glabrous or with diverse indumentum   (30)
30 (29) Leaves 4-12 per whorl, at least middle stem nodes with 6 or more leaves   (31)
+ Leaves 4, very rarely more per whorl   (33)
31 (30) Leaves oblanceolate, base cuneate to acute; petioles 0.6-3.5 cm.   36 R. truppeliana
+ Leaves ovate to suborbicular or lanceolate to oblong-lanceolate, base truncate, rounded, cordulate, or cordate; petioles 1-11 cm   (32)
32 (31) Leaves ovate to suborbicular, largest mostly longer than 4 cm, length/breadth index 1.2-1.5, base cordulate or cordate; petioles 2-11 cm.   31 R. sylvatica
+ Leaves lanceolate to oblong-lanceolate, largest mostly shorter than 4 cm, length/breadth index 2.5-4, base truncate, rounded, or cordulate to cordate; petioles 1-9 cm.   5 R. cordifolia
33 (30) Stems, leaves abaxially, and/or outside of corolla moderately to densely hirtellous or hispidulous with trichomes regularly hooked at apex; leaves small, 0.8-3.5 × 0.3-1.5 cm.   19 R. oncotricha
+ Stems, leaves, and corollas outside glabrous, or with diverse indumentum, but never with regularly hooked hairs; leaves larger, 0.7-13 × 0.3-6.5 cm   (34)
34 (33) Leaves drying thickly leathery, oblong-ovate to elliptic, apex obtuse.   6 R. crassipes
+ Leaves drying papery to leathery, ovate, oblong-lanceolate, ovate-lanceolate, oblong-ovate, cordiform, suborbicular, or lanceolate, apex subacute, acuminate, caudate, or obtuse and cuspidate   (35)
35 (34) Dried plants flushed with red, particularly on lower leaf side; corolla rotate, purplish red, red, or orange, with spreading lobes of 1.2-1.5 mm; mature fruit dark red.   17 R. manjith
+ Dried plants green, gray, or yellowish (if rarely flushed with red then corollas campanulate with reflexed lobes); corolla white, yellow, greenish, or red; mature fruit black, dark blue, or orange   (36)
36 (35) Corollas (sub)campanulate, tube (0.5-)0.8-1.2 mm, lobes ± reflexed, 1.2-1.5 mm   (37)
+ Corollas rotate, fused part 0.2-0.5 mm, lobes ± spreading   (39)
37 (36) Stems 4-ridged to markedly winged; leaves lanceolate, length/breadth index more than 3.   1 R. alata
+ Stems quadrangular but never winged; leaves broader, length/breadth index less than 3   (38)
38 (37) Leaves of main stems ovate-cordiform to suborbicular-cordiform, ± as long as wide or slightly longer than wide, when dry adaxially mealy green or pale green.   20 R. ovatifolia
+ Leaves lanceolate, oblong-ovate, oblong-suborbicular, or ovate, 2-3 × as long as wide, when dry green, brownish green, black, or perhaps red.   22 R. podantha
39 (36) Corollas purplish red, with lobes 3-4 mm.   18 R. membranacea
+ Corollas white, yellow, greenish yellow, or purplish red, with lobes 1-2.5 mm   (40)
40 (39) Corollas pale yellow to white, with lobes 2-2.5 mm.   21 R. pallida
+ Corolla variously colored, with lobes 1-1.5 mm   (41)
41 (40) Leaves linear to narrowly lanceolate, 5-10 × as long as wide.   27 R. salicifolia
+ Leaves broader, oblong-lanceolate, oblong-ovate, ovate, cordiform, or suborbicular, not more than 4 × as long as wide   (42)
42 (41) Leaves ovate to suborbicular, length/breadth index 1-1.8, base cordate or cordulate   (43)
+ Leaves lanceolate to oblong-lanceolate, attenuate toward apex, length/breadth index 2.5-4, lateral veins never impressed and tertiary venation less visible, base truncate, rounded, or cordulate   (44)
43 (42) Largest leaves mostly shorter than 4 cm, usually cuspidate or apiculate toward apex, length/breadth index 1-1.8, drying ± thickly papery, blackening, with lateral veins usually ± impressed and tertiary venation visible; petioles 0.5-5 cm.   2 R. argyi
+ Largest leaves mostly longer than 4 cm, usually attenuate toward apex, length/breadth index 1.2-1.5, drying thinly papery, often remaining greenish, lateral veins never impressed and tertiary venation less visible; petioles 2-11 cm.   31 R. sylvatica
44 (42) Flowers white; Taiwan.   14 R. linii
+ Flowers purplish red, greenish, yellowish, or white; mainland   (45)
45 (44) Stems smooth or sparsely aculeolate; flowers purplish red, greenish yellowish, or whitish; fruit 3.5-4 mm in diam., black at maturity.   37 R. wallichiana
+ Stems rather markedly or sparsely aculeolate; flowers greenish, yellowish, or whitish; fruit 4-6(-7) mm in diam., orange at maturity.   5 R. cordifolia

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