Cerastium

Herbs, annual, winter annual, or perennial. Taproots slender, perennial taxa often rhizomatous, rooting at nodes. Stems ascending to erect or decumbent, simple or branched, terete. Leaves basally connate, petiolate (basal in some species) or sessile (cauline); blade 1–5-veined, linear or elliptic to broadly ovate, not succulent (except in C. bialynickii, C. regelii, and C. viride), apex acute to obtuse. Inflorescences terminal, open or congested cymes, or flowers solitary, axillary (racemosely arranged in C. axillare); bracts paired, foliaceous or reduced, herbaceous or often with scarious margins. Pedicels erect, sometimes reflexed or hooked at apex in fruit, or flowers sometimes subsessile (C. regelii). Flowers bisexual, occasionally unisexual and pistillate; perianth and androecium hypogynous or weakly perigynous; hypanthium minimal; sepals (4–)5, distinct, green (red-tipped in C. glomeratum and C. pumilum, often violet-tipped in C. alpinum, purple in C. bialynickii, turning pale orange-brown in fruit in C. texanum), elliptic to ovate, 3–12 mm, herbaceous, margins translucent to purplish, scarious, apex acute, acuminate, or obtuse, not hooded; petals (4–)5 or sometimes absent, white (purple tinged in C. pumilum and C. regelii), clawed, blade apex 2-fid 1/5–1/2 of length, notched, or emarginate; nectaries at base of filaments opposite sepals; stamens usually 10, sometimes 5 or 8, occasionally 4; filaments distinct, inserted at base of ovary; staminodes absent or 1–4 (via anther abortion), linear; styles (3–)5(–6), clavate to filiform, 0.5–2 mm, glabrous proximally; stigmas (3–)5(–6), subterminal to linear along adaxial surface of styles, roughened to papillate (30×). Capsules oblong or cylindric, usually ± curved, opening by 10, or occasionally 6 or 8, erect or spreading, convolute or revolute teeth, longer than sepals; carpophore absent. Seeds 15–150+, orange to brown, angular-obovate, often with abaxial groove, laterally compressed, papillate-tuberculate, marginal wing absent, appendage absent. x = [9?, 13, 15] 17, 18, 19.

Distribution

Worldwide, but mainly north-temperate region.

Discussion

Species ca. 100 (27 in the flora).

Two names that appear in many North American treatments, Cerastium viscosum Linnaeus and C. vulgatum Linnaeus, have been proposed for rejection (N. J. Turland and M. Wyse Jackson 1997) because they have been a long-standing source of confusion. American authors have frequently applied C. viscosum to C. glomeratum Thuillier but most of the possible lectotypes are referable to C. fontanum. Similarly C. vulgatum has been used for C. fontanum Baumgarten. However the possible lectotypes of C. vulgatum are mixed and most are referable to C. arvense, C. fontanum, and C. glomeratum.

I have not attempted to present an infrageneric classification for Cerastium. Several species groupings can be recognized based on capsule structure. Examples include species with the capsule teeth revolute (coiled outwards like a watch spring), e.g., C. maximum and C. texanum, whereas in most of our species the teeth are erect with their margins outwardly rolled (convolute). Also C. cerastoides is anomalous in having three styles, a straight ovoid-conic capsule, and deeply bilobed petals—characters that have led some authors to place it in the genus Stellaria. Accepting the most recent infrageneric classification (B. K. Schischkin 1936), even with subsequent modifications, does not appear to be warranted. Additional study is needed to determine relevant species relationships within the genus.

While the base chromosome number for Cerastium is often cited as x = 9, only a single count of 2n = 18 is known; see C. Favarger and M. Krähenbühl (1996) for a discussion of the diverse cytological conditions found in Cerastium.

Excluded species:

Cerastium clawsonii Correll, described from Texas, is a synonym of Linum hudsonioides Planchet (R. L. Hartman 1979).

Selected References

Böcher, T. W. 1977. Cerastium alpinum and C. arcticum, a mature polyploid complex. Bot. Not. 130: 303–309.

Brysting, A. K. and R. Elven. 2000. The Cerastium alpinum–C. arcticum complex (Caryophyllaceae): Numerical analyses of morphological variation and a taxonomic revision of C. arcticum Lange s.l. Taxon 49: 189–216.

Good, D. A. 1984. Revision of the Mexican and Central American species of Cerastium. Rhodora 86: 339–379.

Hultén, E. 1956. The Cerastium alpinum complex. A case of world-wide introgressive hybridization. Svensk Bot. Tidsk. 50: 411–495.

Lower Taxa

Cerastium aleuticum, Cerastium alpinum, Cerastium arcticum, Cerastium arvense, Cerastium axillare, Cerastium beeringianum, Cerastium bialynickii, Cerastium brachypetalum, Cerastium brachypodum, Cerastium cerastoides, Cerastium dichotomum, Cerastium diffusum, Cerastium dubium, Cerastium fastigiatum, Cerastium fischerianum, Cerastium fontanum, Cerastium glomeratum, Cerastium maximum, Cerastium nutans, Cerastium pumilum, Cerastium regelii, Cerastium semidecandrum, Cerastium terrae-novae, Cerastium texanum, Cerastium tomentosum, Cerastium velutinum, Cerastium viride

Key

1	Capsules straight, teeth becoming outwardly coiled	> 2
1	Capsules usually curved (rarely straight), teeth erect or sometimes spreading, never coiled, margins convolute	> 3
2	Petals less than 10 mm	Cerastium texanum
2	Petals (15-)18-25 mm	Cerastium maximum
3	Plants annual, with all shoots producing flowers	> 4
3	Plants perennial, often with nonflowering shoots	> 15
4	Styles 3-4(-5); capsules with 6, 8 (10) teeth	> 5
4	Styles 5; capsules with 10 teeth	> 6
5	Styles 4(-5); stamens 4(-5); capsules 1-1.5 times as long as sepals; cauline leaves ovate to oblong-ovate	Cerastium diffusum
5	Styles 3(-4); stamens 10; capsules ca. 2 times as long as sepals; cauline leaves linear to linear-lanceolate	Cerastium dubium
6	Bracts, at least distalmost, with scarious margins	> 7
6	Bracts all completely herbaceous	> 9
7	Stamens 10	Cerastium fontanum
7	Stamens 5	> 8
8	Sepals and distal bracts with broad, scarious margins; petal veins not branched	Cerastium semidecandrum
8	Sepals and distal bracts with very narrow, scarious margins; petal veins branched	Cerastium pumilum
9	Sepals with long hairs exceeding sepal tips	> 10
9	Sepals with hairs shorter than sepal tips	> 11
10	Pedicels shorter than capsules; cauline leaf blades broadly ovate or elliptic-ovate	Cerastium glomeratum
10	Pedicels longer than capsules; cauline leaf blades lanceolate or elliptic	Cerastium brachypetalum
11	Flowers racemosely arranged singly in axils of foliaceous bracts along length of stem	Cerastium axillare
11	Flowers in terminal dichotomous cymes or clusters	> 12
12	Capsules narrowly conic, straight; stamens 5; pedicels shorter than sepals	Cerastium dichotomum
12	Capsules cylindric, curved; stamens 10; pedicels shorter than, equaling, or usually longer than sepals	> 13
13	Pedicels equaling or shorter than capsules, often becoming deflexed proximally	Cerastium brachypodum
13	Pedicels longer than capsules, sharply deflexed distally	> 14
14	Sepals ovate-lanceolate, apex broadly acute to obtuse, inner with broad, scarious margins (ca. as wide as herbaceous center); mid-stem leaf blades lanceolate to narrowly elliptic, 10-60 × 3-15 mm; capsules (9-)10-12(-13) mm	Cerastium nutans
14	Sepals narrowly lanceolate, apex sharply acute to acuminate, inner with narrow, scarious margins (narrower than herbaceous center); mid-stem leaf blades linear-lanceolate, 20-70 × 1.5-6 mm; capsules (5-)7-10(-11) mm	Cerastium fastigiatum
15	Styles 3 (rarely to 6); capsules straight, ovoid-conic, oblong after dehiscence, teeth 6 (rarely to 12)	Cerastium cerastoides
15	Styles 5; capsules usually curved, rarely straight, cylindric (rarely broadly conic), teeth 10	> 16
16	Small tufts of leaves in axils of mid and proximal stem leaves	> 17
16	Small tufts of leaves usually absent from axils of mid and proximal stem leaves (normal leafy shoots may be present)	> 20
17	Petals 7.5-9 mm; sepals 3.5-6(-7) mm; flowering stems 5-20(-30) cm; anthers 0.8-0.9 mm	Cerastium arvense
17	Petals 10-15 mm; sepals 5-9 mm; flowering stems 15-45 cm; anthers 0.9-1.2 mm	> 18
18	Plants taprooted, tufted, with or without short, nonflowering, leafy shoots; pubescence on proximal stem spreading; e North America	Cerastium velutinum
18	Plants with long-creeping rhizomes; pubescence on proximal stems deflexed	> 19
19	Capsules 2.5-4 mm wide; sepals 5-7 mm; seeds 0.6-1.2 mm; introduced lawn weed	Cerastium arvense
19	Capsules 4-5 mm wide; sepals 6-9 mm; seeds 1-1.5 mm; Pacific coastal region	Cerastium viride
20	Leaf surfaces obscured by dense white tomentum	Cerastium tomentosum
20	Leaf surfaces clearly visible through pubescence or leaf blades glabrous	> 21
21	Long flexuous hairs present on stems and/or leaf blades	Cerastium alpinum
21	Long flexuous hairs absent, pubescence of straight or deflexed, short or long hairs	> 22
22	Gland-tipped hairs absent, pubescence eglandular throughout	> 23
22	Gland-tipped hairs present at least in inflorescences	> 24
23	Inflorescences with 3+ flowers; stems 10-45 cm; leaves not marcescent; ubiquitous weed	Cerastium fontanum
23	Inflorescences with 1(-3) flowers; stems 3-7 cm; proximal leaves marcescent; w arctic native	Cerastium aleuticum
24	Testa of seeds inflated, loose (rubs off when rolled between finger and thumb); Newfoundland	Cerastium terrae-novae
24	Testa of seeds not inflated, closely and firmly enclosing seed; North America, rarely in Newfoundland	> 25
25	Plants pulvinate; stems 1-10 cm	> 26
25	Plants rhizomatous, mat-forming or tufted, not pulvinate; stems 5-50 cm	> 27
26	Plants rarely flowering; leaf blades subglabrous or with few colorless cilia	Cerastium regelii
26	Plants normally flowering; leaf blades densely hispid with long, fuscous hairs	Cerastium bialynickii
27	Petals ± equaling sepals	> 28
27	Petals 1.5-2 times as long as sepals	> 29
28	Proximal bracts foliaceous	Cerastium beeringianum
28	Proximal bracts herbaceous, lanceolate, reduced	Cerastium fontanum
29	Sepals 6-11 mm, narrowly lanceolate-triangular, apex acute or acuminate, scarious margins narrow	> 30
29	Sepals 3-7 mm, lanceolate to broadly elliptic, apex obtuse to ± acute, scarious margins broad	> 31
30	Apices of mid and distal stem leaf blades acute; pubescence on stem and leaf blades long, dense, yellowish; inflorescences 2-10-flowered; w arctic	Cerastium fischerianum
30	Apices of mid and distal stem leaf blades usually round and obtuse; pubescence colorless to somewhat fuscous; inflorescences 1-3-flowered; e arctic	Cerastium arcticum
31	Sepals with ± acute apex; leaf blades not succulent, pubescent, those on flowering shoots with ± acute apex; petals usually equaling, rarely to 2 times as long as sepals; plants taprooted, forming clumps, rarely rhizomatous	Cerastium beeringianum
31	Sepals with obtuse apex; leaf blades succulent, subglabrous to ciliate with long, colorless hairs, rotund, obovate, broadly elliptic, or broadly lanceolate, apex obtuse; petals 1.5-2 times as long as sepals; plants strongly rhizomatous with nonflowering, creeping shoots 6-30 cm	Cerastium regelii