Micranthes
Micranthes tenuis
saxifrage
slender saxifrage
± erect, leafless, 2–125 cm.
basal, (proximally cauline and crowded in M. tolmiei);
stipules absent;
petiole present (absent in M. bryophora, M. tolmiei; ± absent in M. foliolosa, M. stellaris; appearing absent in M. tempestiva);
blade obtrullate, spatulate, fan-shaped, or obovate to oblanceolate, linear to oblong, elliptic or rhombic, to lanceolate, ovate, triangular, deltate, round, or reniform, lobed or unlobed, base attenuate or cuneate to truncate or cordate, ultimate margins entire, crenate, serrate, or dentate, (without lime-secreting hydathodes), apex acute to obtuse or rounded;
venation pinnate or palmate.
basal;
petiole broad, flattened, 0.2–1 cm;
blade ± obovate to ± obtrullate, 0.5–1.5 cm, ± coriaceous, base ± attenuate to ± cuneate, margins serrate to dentate on distal 1/3–2/3, sometimes ciliate, surfaces glabrous or glabrate abaxially (rarely sparsely reddish brown-hairy).
cymes or thyrses, sometimes solitary flowers, from terminal buds in rosettes, 2–70+[–1000]-flowered, (flowers sometimes replaced by bulbils in M. bryophora, M. ferruginea, M. foliolosa, M. petiolaris, M. stellaris), (scapose), bracteate; (bracts reduced or sometimes leaflike, only proximal in M. tolmiei).
usually 2–10-flowered, ± capitate cymes, sometimes solitary flowers, (1–)2–7(–11) cm, hairy or glabrous proximally, glabrate or ± purple-tipped stipitate-glandular distally. (Pedicels proximal ± elongate.) Flowers: sepals erect, ovate to deltate;
petals white with purple margins, usually pink or purple tinged, not spotted, obovate to oblong, clawed, 2–3 mm, usually slightly longer than sepals;
filaments linear, flattened;
pistils connate to 1/2 their lengths;
ovary 1/2 inferior, appearing more superior in fruit.
radially symmetric (± bilaterally symmetric in M. ferruginea, M. petiolaris);
hypanthium free from or 1/4–3/4 adnate to ovary, free to 0.5 mm, usually green, rarely purplish;
sepals 5, green, sometimes reddish at tips;
petals 5 (absent or 1–5 in M. apetala, M. subapetala), usually white or cream, sometimes greenish, yellowish, pinkish, pink, purplish, purple, or reddish purple, sometimes purple-margined, sometimes orange-, yellowish green-, or yellow-spotted;
nectary disc present or not;
stamens 10, (distinct);
filaments linear and ± flattened or club-shaped;
pistils 2(–3+), 2(–3)-carpellate, carpels distinct or connate to ca. 1/2 their lengths (rarely more);
ovary superior or ± inferior, sometimes appearing more superior in fruit, 2(–3)-locular;
placentation axile (when connate);
styles 2(–3);
stigmas 2–3.
folliclelike or 2(–3)-beaked.
reddish to purplish, folliclelike.
brown, oblong, ellipsoid, or ovoid, longitudinally ribbed (ribs ribbonlike or pectinate).
= 8.
= 20.
Micranthes
Micranthes tenuis
Species 68–93 (45 in the flora).
The ovules of Micranthes species are unitegminate, except those of M. merkii and M. tolmiei (sect. Merkianae), which are bitegminate. Pollen exine is reticulate. These characters help distinguish Micranthes from Saxifraga (see discussion for differences among the genera).
Some circumboreal species (e.g., Micranthes nelsoniana), which show only slight variation in Europe (D. A. Webb and R. J. Gornall 1989), are more variable in North America.
Molecular phylogenies (D. E. Soltis et al. 2001, and references therein) have shown that Saxifraga in the broad sense is not monophyletic and comprises two main lineages, Saxifraga in the narrow sense and Micranthes, which are not sister to each other (for morphologic differences, see discussion of 23. Saxifraga). We recognize these two as distinct genera, as well as the monospecific Cascadia.
Supernumerary chromosomes have been reported in some species (D. E. Soltis 1983), leading to doubts about the accuracy of some reported chromosome numbers, especially those published before 1950. There is also well-documented and extensive occurrence of polyploidy and dysploidy (sometimes reported as aneuploidy) throughout the genus (P. E. Elvander 1984; D. A. Webb and R. J. Gornall 1989).
The stigmas and styles are typically two (except for three in Micranthes texana); occasional flowers on plants in some species may 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 the flowering stage.
D. A. Webb and R. J. Gornall (1989) provided much ecological and horticultural information on the few European species of the genus.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Micranthes tenuis is morphologically distinguished from M. nivalis only with great difficulty. D. A. Webb and R. J. Gornall (1989) claimed that chromosome number is one of the chief reasons for continuing to recognize the species and, indeed, their enumeration of morphologic differences is not entirely convincing. Occasionally, both species appear to occur in the same populations. The generally smaller size, tendency to glabrousness, fewer number of flowers, and petal color variations reasonably distinguish M. tenuis. Depauperate specimens of M. nivalis are particularly difficult to separate from M. tenuis except for their very consistent hairiness and white petals. Due to the morphologic confusion, exact distributions are difficult to assess and chromosome number reports may be doubtful (D. L. Krause and K. I. Beamish 1973). A thorough systematic study is needed.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Inflorescences with all or some flowers replaced with bulbils | → 2 |
1. Inflorescences without bulbils | → 6 |
2. Plants tufted to mat-forming, with ± branched caudices or stolonlike rhizomes. | M. stellaris |
2. Plants usually solitary or tufted, with caudices | → 3 |
3. Leaf blade margins entire, subentire, or toothed distally; inflorescences narrow, cylindric or open; petals each with 1-2 yellow spots | → 4 |
3. Leaf blade margins coarsely toothed; inflorescences open; petals: 3 with 2 yellow spots and 2 without spots, or all not spotted | → 5 |
4. Leaf blades oblanceolate; pedicels erect to ascending. | M. foliolosa |
4. Leaf blades linear to elliptic; pedicels reflexed. | M. bryophora |
5. Leaf blades usually fleshy, margins usually with fewer than 12 coarse teeth; petioles indistinct; inflorescence bracts reduced; w North America | M. ferruginea |
5. Leaf blades thin, not fleshy, margins with 15+ lobelike teeth; petioles distinct; inflorescence bracts leaflike, gradually reduced distally; e North America. | M. petiolaris |
6. Ovaries ca. 1/2 inferior to inferior (sometimes appearing more superior in fruit) | → 7 |
6. Ovaries ± superior to at most 1/2 inferior (hypanthium to 1/3 adnate to ovary) | → 29 |
7. Leaf blade margins serrate or toothed distally; pistils connate 1/2+ their lengths | → 8 |
7. Leaf blade margins entire to subentire or apically denticulate, or crenulate, denticulate, serrate, or dentate on distal 2/3 to throughout; pistils connate to 1/2 their lengths | → 10 |
8. Leaf blades broadly obovate to round; petals ± clawed, 3.5-5 mm. | M. unalaschcensis |
8. Leaf blades rhombic to fan-shaped, sometimes nearly round, or oblanceolate to spatulate; petals not clawed, 2-4 mm | → 9 |
9. Leaf blades oblanceolate to narrowly oblanceolate or narrowly spatulate, sometimes ± narrowly obovate, margins (3-)5-7(-9)-toothed (teeth 0.5 mm); inflorescence axes and branches glabrous. | M. razshivinii |
9. Leaf blades rhombic to fan-shaped, sometimes nearly round, margins 7-11-toothed (teeth 1-3 mm); inflorescence axes glabrous or sparsely long-hairy, branches ± densely long-hairy. | M. calycina |
10. Petals (1-)5 and pink to purple, or 1-5 and white to greenish white or cream, or absent | → 11 |
10. Petals 5, white to greenish white, cream, or, rarely, purple, sometimes pink or purplish tinged | → 14 |
11. Inflorescences glomerate, congested; petals absent or white to greenish white. | M. apetala |
11. Inflorescences spikelike, constricted or open; petals white, cream, or pink to purple | → 12 |
12. Leaf blades ovate to elliptic, 2-6 cm. | M. hieraciifolia |
12. Leaf blades linear to elliptic, ovate to obovate, or oblanceolate, 3-25 cm | → 13 |
13. Inflorescences ± constricted to ± open thyrses; petals usually absent, sometimes 1-5, 1-2 mm; Rocky Mountains. | M. subapetala |
13. Inflorescences open, often lax thyrses; petals 5, 2-3 mm; e North America. | M. pensylvanica |
14. Leaf blades linear to oblanceolate or obovate, or elliptic to ovate; petioles indistinct | → 15 |
14. Leaf blades ± round to ovate or triangular, elliptic, or oblong, or, rarely, obovate, obtrullate, or deltate; petioles distinct | → 18 |
15. Inflorescences 3-10(-15) cm; petals shorter than sepals. | M. tempestiva |
15. Inflorescences usually 15-125 cm; petals equaling or longer than sepals, sometimes shorter | → 16 |
16. Leaf blade margins serrate to dentate, surfaces densely tangled-hairy; inflorescences flat-topped thyrses. | M. hitchcockiana |
16. Leaf blade margins entire or nearly so or serrulate to denticulate, surfaces glabrous, sparsely hairy, or densely short-hairy; inflorescences conic to cylindric thyrses | → 17 |
17. Leaf blade surfaces glabrous or sparsely hairy (margins ciliate); petals broadly elliptic to obovate and to 2 times as long as sepals, sometimes oblanceolate and equaling or shorter than sepals; w North America. | M. oregana |
17. Leaf blade surfaces short-hairy; petals linear to narrowly elliptic, longer than sepals; e North America. | M. pensylvanica |
18. Leaf blade margins serrate to crenate or dentate, rarely subentire | → 19 |
18. Leaf blade margins entire or subentire to crenulate or denticulate | → 24 |
19. Inflorescences lax, open (with distant lateral branches) | → 20 |
19. Inflorescences ± congested, glomerate or capitate to spicate | → 21 |
20. Sepals reflexed, sometimes spreading. | M. californica |
20. Sepals erect. | M. eriophora |
21. Inflorescences yellow- to cream-tipped stipitate-glandular; petals white, 1.5+ times as long as sepals. | M. rhomboidea |
21. Inflorescences purple- to red-tipped stipitate-glandular, sometimes glabrous proximally or glabrate distally; petals white, sometimes pink- or purple-tipped, margined, or tinged, equaling or slightly longer than sepals | → 22 |
22. Abaxial leaf surfaces glabrate (margins sometimes ciliate); petals white with purple margins, usually pink or purple tinged. | M. tenuis |
22. Abaxial leaf surfaces ± densely, tangled, reddish brown-hairy; petals white (sometimes pink tinged) | → 23 |
23. Inflorescences (5-)10-40-flowered, congested, almost capitate, (3-)7-20 cm; leaf blades ovate to ± round, sometimes elliptic or oblong; arctic and alpine North America | M. nivalis |
23. Inflorescences 3-10-flowered, subcapitate to spicate, 2-10 (-15) cm; leaf blades obtrullate or obovate to ovate; Gaspé Peninsula. | M. gaspensis |
24. Inflorescences at least somewhat congested, conic or capitate, 3.5-15(-35) cm | → 25 |
24. Inflorescences lax, cylindric to conic thyrses, (10-)15-50 cm | → 27 |
25. Carpels 3+. | M. texana |
25. Carpels 2(-3+) | → 26 |
26. Inflorescences densely stipitate-glandular; leaf blades narrowly to broadly ovate, surfaces hairy. | M. integrifolia |
26. Inflorescences sparsely stipitate-glandular; leaf blades obovate to elliptic, surfaces glabrous or sparsely hairy | M. aprica |
27. Inflorescences cylindric, with ± compact lateral cymules; petals 1-1.9 mm, equaling or shorter than sepals. | M. nidifica |
27. Inflorescences conic, with ± open cymules on lateral branches; petals 2-4 mm, longer than sepals | → 28 |
28. Plants solitary or in clumps, caudices often with bulbils; leaf blades usually longer than petioles. | M. integrifolia |
28. Plants often mat-forming, long, thin, rhizomatous; leaf blades usually equaling or shorter than petioles. | M. fragosa |
29. Leaves cauline, proximally crowded; sepals erect to spreading. | M. tolmiei |
29. Leaves basal; sepals reflexed, sometimes spreading or ascending to erect | → 30 |
30. Pistils connate 1/2+ their lengths | → 31 |
30. Pistils distinct almost to base | → 44 |
31. Capsules dark purple or purple-black | → 32 |
31. Capsules green to yellow and purple-tinged, purple, or distal 1/2 purple | → 36 |
32. Filaments club-shaped. | M. nelsoniana |
32. Filaments linear, flattened | → 33 |
33. Leaf blades somewhat reniform, ± evenly lobed, base cordate to truncate, margins entire; inflorescences sparsely purple-tipped stipitate-glandular. | M. nudicaulis |
33. Leaf blades round or obovate to oblanceolate or spatulate, or rhombic to fan-shaped, unlobed, base cuneate to attenuate, margins toothed distally; inflorescences densely tangled-hairy or glabrous | → 34 |
34. Leaf blades broadly obovate to round, base cuneate; petals 3.5-5 mm | M. unalaschcensis |
34. Leaf blades oblanceolate to narrowly oblanceolate or narrowly spatulate, or rhombic to fan-shaped, sometimes nearly round, base attenuate to cuneate; petals 2-4 mm | → 35 |
35. Leaf blades oblanceolate to narrowly oblanceolate or narrowly spatulate, sometimes ± narrowly obovate, margins (3-)5-7(-9)-toothed (teeth 0.5 mm); inflorescence axes glabrous, branches glabrous. | M. razshivinii |
35. Leaf blades rhombic or fan-shaped, margins 7-11-toothed (teeth 1-3 mm); inflorescence axes glabrous or sparsely long- hairy, branches ± densely long tangled hairy | M. calycina |
36. Leaf blades round, reniform, or spatulate to obovate; filaments ± club-shaped | → 37 |
36. Leaf blades linear or elliptic to oblanceolate, obovate, or spatulate; filaments linear, flattened | → 40 |
37. Leaf blades spatulate to obovate, base cuneate to slightly attenuate. | M. lyallii |
37. Leaf blades round to ovate or reniform, base cordate to truncate | → 38 |
38. Inflorescences open, lax thyrses. | M. odontoloma |
38. Inflorescences ± congested, spikelike to glomerulate, sometimes conic thyrses | → 39 |
39. Inflorescences ± congested, conic to glomerate thyrses; petals white to pinkish, rarely orange-spotted; filaments distinctly club-shaped. | M. nelsoniana |
39. Inflorescences spikelike thyrses; petals cream to yellowish; filaments narrowly club-shaped. | M. spicata |
40. Plants tufted or mat-forming, with ± branched caudices or stolonlike rhizomes; inflorescences open, lax cymes. | M. stellaris |
40. Plants solitary or tufted, with caudices; inflorescences cylindric or open, lax thyrses | → 41 |
41. Leaf blades linear to elliptic or oblanceolate, margins entire or subentire to 1-3-toothed distally; petals each with 1-2 yellow spots | → 42 |
41. Leaf blades spatulate to obovate or oblanceolate, margins coarsely toothed in distal 1/3+; petals: 3 with 2 yellow spots, 2 without spots | → 43 |
42. Leaf blades oblanceolate; pedicels erect to ascending. | M. foliolosa |
42. Leaf blades linear to narrowly elliptic; pedicels reflexed. | M. bryophora |
43. Leaves ± fleshy; petioles indistinct; blade margins usually with fewer than 12 coarse teeth; inflorescence bracts usually reduced; w North America. | M. ferruginea |
43. Leaves thin; petioles distinct; blade margins with 15+ lobelike teeth; inflorescence bracts leaflike; e North America. | M. petiolaris |
44. Petals white, each with 1-2 greenish to yellow spots (sometimes faded in dried material); filaments usually strongly club-shaped or petaloid | → 45 |
44. Petals white to greenish, sometimes purplish tipped or margined, usually not spotted; filaments linear, flattened or slightly club-shaped | → 49 |
45. Leaf blades lanceolate to oblanceolate, base attenuate; petioles ± indistinct (broad). | M. micranthidifolia |
45. Leaf blades ovate or elliptic to oblong, sometimes almost orbiculate, base ± attenuate to ± truncate; petioles distinct | → 46 |
46. Leaf blades densely white- or reddish brown-hairy; petal spots usually distinct even in dried material; filaments longer than petals | → 47 |
46. Leaf blades glabrate adaxially; petal spots often faded in dried material; filaments ± equaling petals | → 48 |
47. Leaf blade margins deeply dentate (teeth 2+ mm); inflorescences open, lax; e North America. | M. caroliniana |
47. Leaf blade margins shallowly serrate (teeth to 1 mm); inflorescences with flowers crowded at branch tips; nw North America. | M. reflexa |
48. Leaf blade margins crenate-serrate (teeth ca. 2 mm); inflorescences open, lax; filaments strongly club-shaped, sometimes petaloid. | M. marshallii |
48. Leaf blade margins shallowly serrate to dentate (teeth usually to 1 mm); inflorescences with flowers ± crowded at tips; filaments club-shaped, not petaloid. | M. idahoensis |
49. Sepals erect to ascending | → 50 |
49. Sepals ascending or spreading to strongly reflexed | → 52 |
50. Petal lengths ca. 2 times sepals; ovaries 1/3-1/2 inferior. | M. eriophora |
50. Petal lengths 2+ times sepals; ovaries ± superior | → 51 |
51. Leaf blade margins irregularly crenate to serrate. | M. virginiensis |
51. Leaf blade margins entire or subentire. | M. palmeri |
52. Leaf blade bases truncate; petals often with 2 faint yellow spots. | M. careyana |
52. Leaf blade bases attenuate to ± truncate; petals usually not spotted (rarely present) | → 53 |
53. Petals greenish, often purple-margined. | M. tischii |
53. Petals white | → 54 |
54. Bracts and sepals often tangled brown-hairy; inflorescences flat-topped. | M. rufidula |
54. Bracts and sepals glabrous, rarely sparsely tangled brown-hairy; inflorescences open and conic or ± flat-topped, or glomerulate | → 55 |
55. Leaf blades oblong to narrowly ovate; inflorescences 5-10(-20)-flowered; sepals strongly reflexed. | M. howellii |
55. Leaf blades ovate to elliptic; inflorescences usually (10-)30+-flowered; sepals ascending to spreading | → 56 |
56. Inflorescences with flowers crowded in 1+ glomerules, branches ascending; ovaries ± superior. | M. occidentalis |
56. Inflorescences open, lax, branches strongly divaricate; ovaries nearly 1/3 inferior. | M. gormanii |
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