Survey of the vascular plants of Alert (Ellesmere Island, Canada), a polar desert at the northern tip of the Americas Author Desjardins, Émilie Author Lai, Sandra Author Payette, Serge Author Dubé, Martin Author Sokoloff, Paul C. Author St-Louis, Annie Author Poulin, Marie-Pier Author Legros, Jade Author Sirois, Luc Author Vézina, François Author Tam, Andrew Author Berteaux, Dominique text Check List 2021 2021-02-09 17 1 181 225 http://dx.doi.org/10.15560/17.1.181 journal article 10.15560/17.1.181 1809-127X Potentilla pulchella R. Brown Figure 15D, E Materials examined. CANADA – Nunavut • Ellesmere Island, CFS Alert; 82°28′04″N , 062°51′28″W ; 31 m a.s.l.; 9 Jul. 2019 ; habitat: xeric in a slope, with till and rocks as substrates, dominated by Salix arctica and Dryas integrifolia ; QFA 0635000. Identification. Plants 2.0– 4.5 cm high; herbaceous; caespitose. Taproot and rhizomes present. Stems 2.0– 5.5 cm long; ascending, decumbent, or prostrate; hairy, with non-glandular hairs. Leaves basal and cauline; heterophyllous; petiolate. Stipules green or reddish-brown; hairy. Petioles 5–28 mm long; hairy, with white nonglandular hairs. Basal leaf blades 10–25 mm long, 10–22 mm wide; pinnate-compound, with 3–5 pinnatisect leaflets distributed along the lower 2/3 of leaf axis. Leaflet blades 6–16 mm long, 4–9 mm wide; obovate; lobed, with 3–7 lanceolate, obtuse lobes; abaxial and adaxial surfaces both hairy, with white long–silky, non-glandular hairs (sometimes adaxial surface glabrate with few hairs); margins revolute and ciliate. Cauline leaf blades simple or ternate-compound. Inflorescence a solitary flower or a cyme, with 2 or 3 flowers. Epicalyx 1–3 mm long, 0.5–1.0 mm wide; oblanceolate. Sepals 5; 3–6 mm long, 2–3 mm wide; ovate; green; surface hairy, with hyaline non-glandular hairs; margins ciliate; apices acute. Petals 5; 3–6 mm long, 2–3 mm wide; obovate; unlobed, slightly lobed, or undulating; yellow. Androecium with 17–22 stamens and 0.4–0.6 mm long anthers. Gynoecium consisting of numerous separate carpels, with 0.9– 1.2 mm long conical styles. Potentilla pulchella can be distinguished from the nine other Potentilla Linnaeus species present on Ellesmere Island ( GBIF 2020) by the pinnate leaves (in contrast to ternate or palmate leaves in P. arenosa (Turczaninow) Juzepczuk subsp. arenosa and subsp. chamissonis (Hultén) Elven & D.F. Murray , P. hyparctica Malte subsp. hyparctica and subsp. elatior (Abromeit) Elven & D.F. Murray , P. nivea Linnaeus , P. subgorodkovii Jurtzev , P. tikhomirovii Jurtzev , P. vahliana Lehmann , and P. vulcanicola Juzepczuk ; Ertter et al. 2014 ); the pinnate leaflets distributed along the 1/6–1/2 and more of the leaf axis (in contrast to 1/6–1/4 of the leaf axis in P. pedersenii (Rydberg) Rydberg and P. rubricaulis Lehmann ; Ertter et al. 2014 ); and the ≤ 3 mm wide petals (in con- trast to all other Potentilla species present on Ellesmere Island, which have ≥ 3 mm wide petals; Ertter et al. 2014 ). At Alert, P. pulchella is highly polymorphic in terms of hairiness. Most individuals have silvery-white appearance due to dense hairs on leaves, whereas few individuals are sparsely hairy ( Fig. 15D, E ). A molecular study of this species on Svalbard has shown that there is nearly no genetic ( RAPD ) variation among subpubescent and pubescent plants ( Hansen et al. 2000 ). Instead, pubescence variation is phenotypic and is associated with different abiotic conditions: pubescent plants growing on cliffs, ridges, scree slopes, and silt shore terraces, and subpubescent plants on gravel shore terraces ( Hansen et al. 2000 ). Salicaceae – Willow family