Flora of North America species comparison

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Micranthes

Micranthes occidentalis

saxifrage

mountain saxifrage, redwool saxifrage, western saxifrage
Habit Herbs, sometimes rhizomatous, sometimes stoloniferous; herbage usually hairy, sometimes stipitate-glandular, sometimes glabrous; caudex or rhizome scaly, sometimes with bulbils. Plants in groups or sometimes almost mat-forming, with bulbils on caudices or rhizomatous.
Flowering stems

± erect, leafless, 2–125 cm.

Leaves

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 flattened, 1–5 cm;

blade ovate to elliptic, 1.5–3.5 cm, ± fleshy, base ± attenuate to ± truncate, margins shallowly, sharply serrate, ciliate, surfaces sparsely tangled, reddish brown-hairy abaxially, glabrous adaxially.
Inflorescences

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 (10–)30+-flowered, flowers crowded into 1+ glomerules in thyrses with ascending branches, 8–30 cm, purple-tipped stipitate-glandular; (bracts glabrous or marginally glandular-ciliate).
Flowers

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.

sepals ascending to spreading, sometimes reflexed in fruit, ovate to oblong, (surfaces glabrous);

petals white, not spotted (spots rarely present), obovate to almost round, clawed, 2–4 mm, to 1.5 times as long as sepals;

filaments linear to very slightly widened near anthers, flattened;

pistils distinct almost to base;

ovary ± superior.
Capsules

folliclelike or 2(–3)-beaked.

greenish or reddish to ± dark purple, folliclelike.
Seeds

brown, oblong, ellipsoid, or ovoid, longitudinally ribbed (ribs ribbonlike or pectinate).

x

= 8.

2n

= 20, 38, 40, 56, 58.

Micranthes

Micranthes occidentalis
Phenology Flowering spring–summer.
Habitat Wet, rocky or gravelly slopes, moist to dry alpine meadows, flushes
Elevation 500-4000 m (1600-13100 ft)
Distribution
North America; Mexico; South America; Eurasia; mostly north-temperate; arctic; and alpine regions
[BONAP county map]
from FNA
AK; ID; MT; NV; OR; SD; WA; WY; AB; BC; SK
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[BONAP county map]
Discussion

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 occidentalis appears closely related to the little-known M. mexicana (Engler & Irmscher) Brouillet & Gornall from Chihuahua, Mexico. The latter is the only species of the genus that occurs in Mexico and not in the United States. Micranthes occidentalis is disjunct between the northern Rocky Mountains and the Cypress Hills of southeastern Alberta and southwestern Saskatchewan, and the Black Hills of South Dakota. It hybridizes with M. idahoensis where their ranges overlap.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
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
Source FNA vol. 8, p. 49. Authors: Luc Brouillet, Patrick E. Elvander†. FNA vol. 8, p. 62.
Parent taxa Saxifragaceae Saxifragaceae > Micranthes
Sibling taxa
M. apetala, M. aprica, M. bryophora, M. californica, M. calycina, M. careyana, M. caroliniana, M. eriophora, M. ferruginea, M. foliolosa, M. fragosa, M. gaspensis, M. gormanii, M. hieraciifolia, M. hitchcockiana, M. howellii, M. idahoensis, M. integrifolia, M. lyallii, M. marshallii, M. micranthidifolia, M. nelsoniana, M. nidifica, M. nivalis, M. nudicaulis, M. odontoloma, M. oregana, M. palmeri, M. pensylvanica, M. petiolaris, M. razshivinii, M. reflexa, M. rhomboidea, M. rufidula, M. spicata, M. stellaris, M. subapetala, M. tempestiva, M. tenuis, M. texana, M. tischii, M. tolmiei, M. unalaschcensis, M. virginiensis
Subordinate taxa
M. apetala, M. aprica, M. bryophora, M. californica, M. calycina, M. careyana, M. caroliniana, M. eriophora, M. ferruginea, M. foliolosa, M. fragosa, M. gaspensis, M. gormanii, M. hieraciifolia, M. hitchcockiana, M. howellii, M. idahoensis, M. integrifolia, M. lyallii, M. marshallii, M. micranthidifolia, M. nelsoniana, M. nidifica, M. nivalis, M. nudicaulis, M. occidentalis, M. odontoloma, M. oregana, M. palmeri, M. pensylvanica, M. petiolaris, M. razshivinii, M. reflexa, M. rhomboidea, M. rufidula, M. spicata, M. stellaris, M. subapetala, M. tempestiva, M. tenuis, M. texana, M. tischii, M. tolmiei, M. unalaschcensis, M. virginiensis
Synonyms Saxifraga occidentalis, Saxifraga allenii, Saxifraga occidentalis var. allenii, Saxifraga occidentalis var. wallowensis, Saxifraga reflexa subsp. occidentalis, Saxifraga saximontana
Name authority Haworth: Syn. Pl. Succ., 320. 1812 , (S. Watson) Small: in N. L. Britton et al., N. Amer. Fl. 22: 144. 1905 ,
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Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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