Cerastium arcticum Lange

Desjardins, Émilie, Lai, Sandra, Payette, Serge, Dubé, Martin, Sokoloff, Paul C., St-Louis, Annie, Poulin, Marie-Pier, Legros, Jade, Sirois, Luc, Vézina, François, Tam, Andrew & Berteaux, Dominique, 2021, Survey of the vascular plants of Alert (Ellesmere Island, Canada), a polar desert at the northern tip of the Americas, Check List 17 (1), pp. 181-225 : 194

Cerastium arcticum Lange

Figure 6A

Materials examined. CANADA – Nunavut • Ellesmere

Island, CFS Alert; 82°25′52″N, 062°07′49″W; 296 m a.s.l.; 16 Jul. 2019; habitat: wetland in a mountain pass, with peat and rocks as substrates, dominated by moss and Saxifraga cernua ; QFA 0635574.

Identification. Plants 1–12 cm high; herbaceous; caespitose. Taproots and rhizomes present. Stems 2–12 cm long; prostrate, or ascending; hairy, with septate glandular hairs and septate non-glandular hairs. Leaves basal and cauline; opposite; subsessile (basal and lower cauline leaves) or sessile (upper cauline leaves). Basal leaf blades 5–12 mm long, 2–5 mm wide; elliptic, lanceolate, obovate, or oblanceolate; abaxial and adaxial surfaces both hairy, with septate glandular hairs and septate nonglandular hairs (hairs 1.0– 3.4 mm long); margins ciliate; apices acute, acuminate, or obtuse. Cauline leaf blades 1.7–3.6 mm long, 0.5–1.2 mm wide; abaxial and adaxial surface both hairy; margins hyaline and ciliate. Inflores- cence a solitary flower or a dichasium, with 2–4 flowers. Bracts 4–9 mm long, 0.8–2.0 mm wide; surface hairy; margins hyaline (0.1–0.2 mm wide) and ciliate. Pedicels hairy. Sepals 5; 5.0– 7.8 mm long, 1–3 mm wide; elliptic or lanceolate; green to purple; hairy, with septate glandular hairs and septate non-glandular hairs; margins hyaline and glabrous; apices acute. Petals 5; 6.0– 9.8 mm long, 2.7–4.0 mm wide; obtriangular or oblanceolate; notched; white. Androecium with 10 stamens and 0.9– 1.5 mm long, yellow anthers. Gynoecium with 5 styles and 1 stigma per style. Fruit a capsule; 9–11 mm long, 3–5 mm wide; cylindrical; straw-colored; ending with 8–10 teeth; glabrous.

Cerastium Linnaeus species can be differentiated from Arenaria Linnaeus and Stellaria Linnaeus species by the petals: Cerastium species have petals cleft at most to 25 %, whereas Arenaria species have unlobed petals and Stellaria species have petals cleft nearly to the base ( Aiken et al. 2007). C. arcticum is very similar to C. alpinum Linnaeus subsp. alpinum and subsp. lanatum (Lamarck) Cesati , C. beeringianum Chamisso & Schlechtendal , and C. bialynickii Tolmatchew that are present on Ellesmere Island ( GBIF 2020), but a few characters help differentiate them. C. arcticum has leaves with hairs that are always> 0.3 mm long, whereas both C. alpinum subspecies have long but also short hairs (<0.3 mm long); bracts have more distinct hyaline margins in both C. alpinum subspecies (0.3–0.8 mm wide) than in C. arcticum (≤ 0.3 mm wide; Blondeau 2015a). As for the differences between C. beeringianum and C. arcticum , hairs on leaves are longer in C. arcticum (≥ 0.9 mm long) than in C. beeringianum (≤ 0.9 mm long); bract leaves of C. arcticum (4–9 mm long) are longer than those of C. beeringianum (2.5–3.0 mm long); and fruits of C. arcticum are also larger (3–5 mm wide) than those of C. beeringianum (2–3 mm wide; Aiken et al. 2007; Blondeau 2015a). C. bialynickii has a pulvinate growth form with short stems (1–10 cm long), whereas C. arcticum , both C. alpinum subspecies, and C. beeringianum have rhizomatous or mat-forming, not pulvinate growth form (cushion-like) with longer stems (5–50 cm long; Morton 2005). The stem length of the specimens of C. arcticum from Alert ranges from 2 to 12 cm and some specimens had a cushion growth form rather than a mat-forming growth form, and therefore do not exactly match the criteria above. Although, C. bialynickii is considered a synonym of C. beeringianum in Aiken et al. (2007), it is treated as a distinct species in FNA (Flora of North America Editorial Committee 2005), Tropicos (2020), and VASCAN ( Brouillet et al. 2010 +; Desmet and Brouillet 2013).