Micranthes tenuis (Wahlenberg) Small

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 : 216-217

Micranthes tenuis (Wahlenberg) Small

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 ; QFA0634988 .

Identification. Plants 3–6 cm high; herbaceous; not caespitose. Fibrous roots present. Stems 1.9–5.0 cm long;

erect; hairy, with septate glandular hairs (0.1–0.5 mm long). Leaves basal; patent or horizontal; alternate; petiolate. Petioles 0.5–3.0 mm long; hairy, with septate glandular hairs. Basal leaf blades 4–10 mm long, 3–7 mm wide; obovate or obtrullate; bases cuneate or attenuate; lobed, with 5–10 triangular, obtuse lobes; green or reddish-purple; abaxial and adaxial surfaces both glabrous; margins glabrous or ciliate, with septate glandular hairs. Inflorescence a solitary flower or a capitate cyme, with 2–5 flowers. Bracts 3–5 mm long, 1.2–2.5 mm wide; ovate or lanceolate; surface glabrous; margins ciliate. Pedicels hairy. Sepals 5; 3–5 mm long, 1.5–2.5 mm wide; elliptic or obovate; green to purple; surface glabrous; margins glabrous; apices obtuse or rounded. Petals 5; 2.5–4.0 mm long, 0.8–2.0 mm wide; obovate; unlobed; pink. Androecium with 8–10 stamens and 0.2–0.4 mm long anthers. Gynoecium with 2 styles.

Four Micranthes Hawort species are present on Ellesmere Island ( GBIF 2020). M. hieraciifolia (Waldstein & Kitaibel ex Willdenow) Haworth , M. nivalis (Linnaeus) Small , and M. tenuis have inflorescences without bulbils, in contrast to M. foliolosa (R. Brown) Gornall , which has bulbils replacing some or all the flowers ( Saarela et al. 2020). The inflorescences, however, differ among the first three species; M. hieraciifolia has spikelike thyrses 2–10 cm long, whereas M. nivalis and M. tenuis have capitate thyrses or capitate cymes 0.5–4.0 cm long ( Saarela et al. 2020). Micranthes tenuis is similar to M. nivalis but the two differ in a few characters: M. tenuis has more slender stems with sparse hairs <1 mm long, whereas stems of M. nivalis are pubescent with hairs> 1 mm long ( Blondeau 2015c); the inflorescence of M. tenuis is a solitary flower or an open capitate cyme with 2–10 distinctly pedicellate flowers, whereas inflorescence of M. nivalis is a compact capitate thyrse with 5–40 densely clustered flowers ( Aiken et al. 2007; Brouillet and Elvander 2009a). Moreover, M. nivalis is mostly found in barren grounds and hummocks, whereas M. tenuis is only found in wet and moist areas such as pond margins, wet meadows, and marshes ( Aiken et al. 2007).