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23. Saxifraga Linnaeus, Sp. Pl. 1: 398. 1753; Gen. Pl. ed. 5, 189. 1754.
Saxifrage [Latin saxum, rock, and frango, to break, alluding to growth in rock crevices and/or medical use for kidney stones]
Luc Brouillet, Patrick E. Elvander
Antiphylla Haworth; Heterisia Rafinesque ex Small; Hirculus Haworth; Leptasea Haworth; Lobaria Haworth; Muscaria Haworth
Herbs perennial (biennial in S. adscendens, annual in S. tridactylites), sometimes rhizomatous, sometimes stoloniferous; caudex not fleshy, scaly, sometimes with bulbils; herbage hairy or stipitate-glandular, sometimes glabrous. Flowering stems ± erect, leafy, 1-40[-100] cm. Leaves in basal rosette and cauline, alternate (opposite in S. nathorstii, S. oppositifolia), cauline reduced; stipules absent; petiole absent or present; blade obovate, oblong, oblong-obovate, elliptic, linear, spatulate, or oblanceolate to ovate, reniform, or round, lobed or unlobed, base cuneate to cordate, ultimate margins entire, crenate, serrate, or dentate, (with lime-secreting hydathodes in S. aizoides, S. nathorstii, S. oppositifolia, S. paniculata), apex acute to obtuse or rounded; venation pinnate or palmate. Inflorescences thyrses or, sometimes, cymes, sometimes solitary flowers, terminal from terminal bud in rosette, 2-200[-1000]-flowered, (some or all flowers replaced by bulbils in S. cernua, S. mertensiana), usually bracteate (ebracteate in S. nathorstii, S. oppositifolia); (bracts leaflike). Flowers [bilaterally symmetric], bisexual (unisexual and plants sometimes gynodioecious, or plants dioecious in S. eschscholtzii); hypanthium free from or 1/4-3/4 adnate to ovary, free from ovary to 0.5 mm, green or pink to purple, (0.1-4 mm); sepals 5, green, sometimes reddish at tips, sometimes ± purple; petals absent or (1-)5, white, cream, yellow, orange, red, pink, or purple, often yellow-, orange-, or red-spotted; nectary disc present or not; stamens 10, (distinct); filaments linear and ± flattened (club-shaped in S. mertensiana); ovary superior to ± inferior, sometimes appearing more superior in fruit, 2-locular, carpels usually (1/4-)1/2 connate proximally or ± distinct; placentation axile (when connate 1/2+ their length) or appearing marginal; styles 2; stigmas 2. Capsules 2(-3)-beaked (± folliclelike in S. oppositifolia). Seeds brown, oblong, ellipsoid, or ovoid, smooth, tuberculate, or papillate. x = 6, 8, 11, 13, 14.
Species ca. 390 (25 in the flora): North America, South America, Eurasia, n Africa; mostly north-temperate, arctic, and montane regions.
Saxifraga has had differing treatments (e.g., J. K. Small and P. A. Rydberg 1905b; H. G. A. Engler and E. Irmscher 1916; P. E. Elvander 1984; D. A. Webb and R. J. Gornall 1989). Most have been based on morphology and cytology. Relationships among species are difficult to assess. The broad Linnaean concept of the genus had been accepted by most recent authors. Molecular phylogenetic data (summarized by D. E. Soltis et al. 2001) show that Saxifraga as traditionally understood is polyphyletic and should be divided into two main groups, Saxifraga in the narrow sense and Micranthes Haworth, the treatment followed here. Other taxa, notably the North American Cascadia, must also be recognized. Cascadia differs from both Saxifraga and Micranthes in its lax, trailing stems and only cauline leaves, its carpels connate only proximally and each independently adnate to the hypanthium, and its spiny seeds; its ovules are bitegmic as in Saxifraga; ovules are unitegmic (except for sect. Merkianae) in Micranthes. In addition, Saxifraga and Micranthes differ by the following traits: leaves basal and cauline (these sometimes reduced and bractlike) in the former versus basal only (or proximally crowded) in the latter (the flowering stems being leafless); carpels usually connate more than one-half versus less than one-half, although there is variation in both genera for this trait; seeds smooth, tuberculate, or papillate versus longitudinally ribbed; and pollen striate or granular versus reticulate (L. Brouillet and R. J. Gornall 2007).
Saxifraga in the narrow sense, as adopted here, includes most sections of the traditional genus as well as a majority of the species. In North America fewer species belong to Saxifraga than to Micranthes. Eight species of Saxifraga are endemic to North America. A single introduced species has established itself in the flora area; other garden species have usually not escaped or were ephemeral. The following species are excluded from this treatment: S. cymbalaria Linnaeus (misidentification of S. sibthorpii Boissier, a garden plant, not established), S. ×geum Linnaeus and S. umbrosa Linnaeus (both misidentifications of S. hirsuta specimens), and S. hirsuta Linnaeus (not established). The report of S. stolonifera Meerburgh (syn. S. sarmentosa Linnaeus f.) from California is old; there has been no recent collection, and that species also is excluded here.
There is extensive occurrence of polyploidy and dysploidy throughout Saxifraga (P. E. Elvander 1984; D. A. Webb and R. J. Gornall 1989).
The stigmas and styles are typically two; occasional flowers on plants in some species have three or, rarely, four stigmas and styles. In addition, ovary position in some taxa can change from mostly inferior at flowering to superior in fruit. Ovary position is described at flowering. Capsules usually have two connate carpels that are distally distinct; in rare cases, carpels are distinct nearly to the base and fruits are folliclelike. Only such exceptions are indicated in descriptions, the usual case being assumed.
SELECTED REFERENCES Calder, J. A. and D. B. O. Savile. 1959b. Studies in Saxifragaceae--II. Saxifraga sect. Trachyphyllum in North America. Brittonia 11: 228-249. Elvander, P. E. 1984. The taxonomy of Saxifraga (Saxifragaceae) section Boraphila subsection Integrifoliae in western North America. Syst. Bot. Monogr. 3: 1-44. Jørgensen, M. H. et al. 2006. Taxonomy and evolutionary relationships in the Saxifraga rivularis complex. Syst. Bot. 31: 702-729. Webb, D. A. and R. J. Gornall. 1989. A Manual of Saxifrages and Their Cultivation. Portland.
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| 1 |
Inflorescences with all or some flowers replaced by bulbils |
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(2) |
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Inflorescences without bulbils |
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(3) |
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| 2 (1) |
Basal leaves usually ephemeral (gradually dying through growing season), leaf blade (3-)5-18(-20) mm, 3-7(-9)-lobed, margins entire; inflorescences with bulbils often replacing all flowers or all flowers except terminal; bracts conspicuous; sepals erect. |
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16 Saxifraga cernua (in part) |
| + |
Basal leaves persistent, leaf blade 20-80(-100) mm, irregularly lobed, margins serrate; inflorescences with bulbils replacing at least some flowers; bracts ± inconspicuous; sepals reflexed (at least in fruit). |
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25 Saxifraga mertensiana (in part) |
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| 3 (1) |
Ovaries 1/2+ inferior (sometimes appearing more superior in fruit) |
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(4) |
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Ovaries ± superior to ca. 1/2 inferior |
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(13) |
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| 4 (3) |
Petals yellow to orange |
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(5) |
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Petals white, cream, pink, or purple, yellowish, greenish, or pink tinged |
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(6) |
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| 5 (4) |
Plants mat- or cushion-forming, not stoloniferous; leaf blade margins usually spinose-ciliate; inflorescences glabrous or clear-tipped stipitate-glandular. |
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3 Saxifraga aizoides |
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Plants in clumps, stoloniferous; leaf blade margins glandular-ciliate; inflorescences purplish-tipped stipitate-glandular. |
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6 Saxifraga flagellaris (in part) |
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| 6 (4) |
Petioles absent; leaf blades leathery, lime-secreting hydathodes present. |
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4 Saxifraga paniculata |
| + |
Petioles usually present; leaf blades thin or ± fleshy (not leathery), lime-secreting hydathodes absent |
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(7) |
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| 7 (6) |
Leaf blades spatulate, obovate, oblanceolate, or elliptic to ovate |
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(8) |
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Leaf blades reniform to orbiculate or round |
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(10) |
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| 8 (7) |
Plants perennial, densely cushion- or loosely mat-forming. |
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24 Saxifraga cespitosa |
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Plants biennial or annual, solitary or tufted |
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(9) |
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| 9 (8) |
Plants biennial, basal leaves persistent; petals (2-)3-6 mm. |
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22 Saxifraga adscendens |
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Plants annual, basal leaves usually withered at flowering; petals 2.5-3 mm. |
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23 Saxifraga tridactylites |
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| 10 (7) |
Plants usually densely (sometimes loosely) tufted, not rhizomatous |
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(11) |
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Plants loosely (sometimes densely) tufted or matted, sometimes solitary, rhizomatous |
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(12) |
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| 11 (10) |
Cauline leaves 3-5 (proximal similar to basal leaves); hypanthium V-shaped in longisection, glabrous or sparsely short stipitate-glandular; sepals 0.7-1 mm wide. |
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19 Saxifraga debilis |
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Cauline leaves 1-3 (dissimilar from basal leaves, reduced); hypanthium U-shaped in longisection, sparsely to densely long stipitate-glandular; sepals 1.5-2.1 mm wide. |
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20 Saxifraga hyperborea |
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| 12 (10) |
Plants green; leaf blades (5-)7.4-11.2(-20) mm, 5-7(-11)-lobed, lobes obtuse, sometimes acute; inflorescences capitate thyrses (flowers subsessile), (3-)5-15(-18) cm; bracts 5-10, leaflike, 3-7-lobed, densely surrounding inflorescence; petals broadly elliptic to obovate. |
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18 Saxifraga bracteata |
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Plants green to purple; leaf blades (2.6-)3.7-5.2(-7.4) mm, 3-5(-7)-lobed, lobes rounded, sometimes ± obtuse; inflorescences cymes (flowers pedicellate), 1.7-7 cm; bracts 2-3, reduced, unlobed or 1-3-lobed, not surrounding inflorescence; petals oblong to elliptic. |
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21 Saxifraga rivularis |
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| 13 (3) |
Leaves mostly opposite, with lime-secreting hydathodes |
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(14) |
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Leaves alternate, without lime-secreting hydathodes |
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(15) |
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| 14 (13) |
Leaf blades oblong to obovate, 2-5 mm; petals purple to pink, rarely white, often drying violet. |
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1 Saxifraga oppositifolia |
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Leaf blades oblanceolate to elliptic, 5-9 mm; petals salmon to flesh colored, sometimes red or orange, rarely yellow, sometimes violet tinged. |
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2 Saxifraga nathorstii |
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| 15 (13) |
Petals yellow to greenish yellow (rarely purple), rarely orange- or red-spotted, sometimes fading when dried |
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(16) |
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Petals white or cream to purple, sometimes yellow-, orange-, or red-, or purple-spotted, sometimes drying to cream or pale yellow |
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(21) |
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| 16 (15) |
Plants loosely tufted and rhizomatous or in solitary clumps and stoloniferous |
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(17) |
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Plants mat- or cushion-forming, rhizomatous |
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(18) |
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| 17 (16) |
Plants loosely tufted, not stoloniferous or sometimes shortly so; leaf blade margins eciliate or sparsely reddish brown-ciliate, surfaces glabrous or sparsely reddish brown-villous; sepal margins reddish brown-ciliate. |
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5 Saxifraga hirculus |
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Plants in solitary clumps, stoloniferous; leaf blade margins glandular-ciliate, surfaces glabrous; sepal margins stipitate glandular-ciliate. |
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6 Saxifraga flagellaris (in part) |
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| 18 (16) |
Flowers unisexual; leaf blade margins stiffly bristly-ciliate. |
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8 Saxifraga eschscholtzii |
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Flowers bisexual; leaf blade margins ciliate (but not stiffly bristly) or eciliate |
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(19) |
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| 19 (18) |
Petals greenish yellow, 2-3 mm. |
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9 Saxifraga aleutica |
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Petals bright golden or pale yellow, rarely purple, 4-8 mm |
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(20) |
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| 20 (19) |
Sepals erect to spreading, margins eciliate or sparsely ciliate; petals pale yellow, rarely purple. |
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7 Saxifraga serpyllifolia (in part) |
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Sepals strongly reflexed, margins eciliate to glandular-ciliate; petals bright golden yellow. |
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10 Saxifraga chrysantha |
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| 21 (15) |
Sepals reflexed (at least in fruit). |
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25 Saxifraga mertensiana (in part) |
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Sepals erect or ascending to spreading |
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(22) |
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| 22 (21) |
Plants solitary or tufted; leaf blades round to reniform, 3-7(-9)-lobed |
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(23) |
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Plants mat-forming; leaf blades linear or lanceolate to elliptic or oblong, oblanceolate, or obovate to spatulate or cuneate, unlobed or with 1-3 apical teeth or lobes |
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(24) |
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| 23 (22) |
Leaf blades lobed less than halfway to midvein; petioles (5-)10-60 (-90) mm. |
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16 Saxifraga cernua (in part) |
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Leaf blades lobed usually more than halfway to midvein; petioles 5-15 mm. |
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17 Saxifraga radiata |
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| 24 (22) |
Leaf blades usually with 1-3 apical teeth or lobes |
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(25) |
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Leaf blades unlobed |
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(27) |
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| 25 (24) |
Leaf apex long spinose-mucronate, margins softly glandular- ciliate. |
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14 Saxifraga tricuspidata (in part) |
| + |
Leaf apex mucronate or not, margins stiffly ciliate |
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(26) |
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| 26 (25) |
Leaf blades spatulate, apex mucronate, margins not cartilaginous, unlobed or minutely 3-toothed or -lobed apically; petals red- or orange-spotted distally. |
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12 Saxifraga vespertina (in part) |
| + |
Leaf blades broadly obovate, apex not or slightly mucronate, margins cartilaginous, prominently 3-lobed apically; petals not spotted. |
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15 Saxifraga taylorii |
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| 27 (24) |
Leaf blades linear, linear-lanceolate, or oblanceolate to narrowly elliptic or cuneate, apex acute, spinose-mucronate |
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(28) |
| + |
Leaf blades linear or oblong to oblanceolate or spatulate, apex rounded or obtuse, sometimes mucronate (but not spinose-mucronate) |
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(29) |
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| 28 (27) |
Leaf blade margins stiffly ciliate. |
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11 Saxifraga bronchialis |
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Leaf blade margins softly glandular-ciliate. |
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14 Saxifraga tricuspidata (in part) |
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| 29 (27) |
Petals usually pale yellow, rarely purple, not spotted. |
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7 Saxifraga serpyllifolia (in part) |
| + |
Petals white to cream, yellow-, orange-, or red- spotted |
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(30) |
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| 30 (29) |
Petals yellow-spotted proximally, red- or orange-spotted distally. |
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12 Saxifraga vespertina (in part) |
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Petals usually yellow-spotted, sometimes sparsely red-spotted proximally. |
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13 Saxifraga cherlerioides |
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List of lower taxa
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