Flora of the Canadian Arctic Archipelago
Brassicaceae (Cruciferae), Draba family.
Published in Denkschr. Königl.-Baier. Bot. Ges. Regensburg 1: 65. 1815.
Type: Type species Braya alpina Sternb. and Hoppe from the European Alps
Vegetative morphology. Plants (1.2–)3.5–20(–33) cm high; perennial herbs (often purple tinged); caespitose. Taproot present. Ground level or underground stems vertical. Caudex present (branched or simple). Aerial stems a small transition zone between taproot and basal leaves, or branching from a tap at or near ground level into two or more branches; erect, or ascending, or decumbent, or prostrate (simple or branched). Aerial stem trichomes appressed, or spreading, or erect. Leaves mainly basal, or basal in a rosette; patent, or erect; alternate; dying annually and non-persistent and marcescent (slightly). Petioles present, or absent; 0–40 mm long (if applicable); winged (conspicuously so at the point of attachment), or not winged; glabrous, or hairy; pilose. Petiole hairs longer than the diameter of the petiole; spreading. Leaf blades simple (sometimes fleshy). Leaf blade bases truncate, or attenuate. Blades (4–)10–40(–80) mm long, (0.3–)0.6–5(–9) mm wide, appressed to the stem or spreading, linear or oblanceolate or spatulate, appearing single-veined or with inconspicuous veins. Blade adaxial surface dull (usually) or shiny, glabrous or glabrescent or hairy, hairs pubescent or pilose or villous (if applicable), hairs simple or branched (bifid or trifid), hairs sparse, hairs white, or translucent. Blade abaxial surface glabrous or glabrescent or hairy, hairs pilose (if applicable), hairs sparse or moderately dense (if applicable), hairs white, hairs curved (or forked), hairs appressed or spreading. Blade margins entire (usually) or dentate (slightly, B. purpurascens), glabrous or with non-glandular hairs or with glandular hairs, with 1–2 teeth on each side of the blade (if applicable); apices acute, or obtuse, or rounded.
Reproductive morphology. Flowering stems conspicuously taller than the leaves (usually), or shorter than the leaves (B. thorild-wulfii when stems are prostrate); with leaves, or without leaves. Flowering stems hairy. Flowering stems pilose, or woolly. Flowering stem hairs simple, or branched; white or translucent. Inflorescences head-like (in flower), or racemose, or head-like (in fruit); dense (in flower), or diffuse (in fruit); elongating as the fruit matures. Pedicels present (ascending or erect, not subtended by bracts, except occasionally the lowermost)); glabrous, or with non-glandular hairs. Flowers per inflorescence 3–12(–15); small; radially symmetrical (actinomorphic). Sepals conventional; 4; free (erect or slightly spreading); (0.6–)1–2 mm long; (1.6–)2–3.5(–3.7) mm wide; green, or purple, or pink; herbaceous, or scarious (on the scarious margins, ovate, sub-equal). Calyx glabrous, or hairy. Calyx hairs pilose, or woolly; white or translucent. Calyx margins ciliate (sometimes, as a tuft of hairs at the tip). Petals conventional; free; 4 (widely spreading); white, or pink, or purple (tinged, especially the claw); obovate, or spatulate; unlobed (truncate); 2–5(–7.5) mm long; 1–3(–4.2) mm wide. Stamens 6; stamen filaments markedly unequal in length; stamen filaments glabrous. Anthers yellow; ovoid, or sub-globose; 0.4–0.9 mm long. Ovary superior; carpels 2; syncarpous. Ovaries pear-shaped, or ovate, or oblong; hairy; pilose, or woolly. Ovary hairs white; spreading; straight, or wavy, or branched. Styles 1; completely fused; thick and short (variable in length); 0.1–1.7 mm long. Stigmas per ovary 1, or 2 (bilobed). Placentation parietal. Ovules per ovary 5–40. Fruit stalked; stalk (1–)2–5(–8) mm long; dry; a silique (often torulose; septum epidermal cells thick-walled and elongated transversely or obliquely in relation to the longitudinal axis of the fruit); ellipsoid, or ovoid, or elongate-cylindrical (1.25 to many times longer than broad, terete or slightly compressed parallel to the septum), or oblong; yellowish, or purple, or green at maturity; (3–)5–15(–17) mm long; (0.6–)1.5–9 mm wide; hairy, or glabrescent; surface venation ribbed, or appearing veinless; not distinctly flattened; dehiscent; shedding the outer walls to expose a thin inner wall, with the seeds attached at the margins on either side. Seeds 5–40 (uniserate or biseriate, oval-ovoid, slightly convex, somewhat beaked, cotyledons incumbent); 1–1.4 mm long; brown, or yellowish.
Chromosome information. 2n = 28, or 42, or 56, or 70.
Ploidy levels recorded 4x, 6x, 10x.
General notes. A relatively small genus of circumboreal arctic, subarctic, and alpine distribution.
Key to species
1a. Stems leafy (usually 2 or more leaves per stem); fruit a silique, linear, sub-cylindrical, 9–33 times longer than wide; seeds uniseriate; walls of septal epidermal cells thick and irregular ... B. humilis
1b. Stems scapose (occasionally with a single leaf or leafy bract); fruit a silique or silicle, ovoid to oblong-lanceolate, never linear, 1.25–8 times longer than wide; seeds biseriate; walls of septal epidermal cells thinner and quite regular ... 2
2a. Fruits ovoid-ellipsoid to oblong-lanceolate, 2.5–8 times longer than wide; stems erect or ascending (rarely decumbent to prostrate) and the petals shorter than 4.7 mm ... B. glabella
2b. Fruits ovoid to globose, 1–2 times longer than wide; stems erect and the petals longer than 4.7 mm or stems decumbent to prostrate and the petals shorter ... 3
3a. Petals 2.0–3.7 mm long, 1.0–1.5 mm broad; styles 0.25–0.75 mm long, stout; stems decumbent to prostrate; found on the northern and western islands of the Canadian Arctic Archipelago ... B. thorild-wulffii
3b. Petals 4.7–6.6 mm long, 3.0–5.1 mm broad; styles 1.25–2.0 mm long, slender; stems erect; known only from the type locality near Cape Bathurst ... B. pilosa
Harris (1985) considered Braya to be a natural group with well-defined genetic boundaries. He revised the treatment of the genus for North America based on studies of morphology (both traditional herbarium studies and numerical analyses), cytology, ecology, and enzyme chemistry. He recognised seven species and six varieties. The taxa relevant to the Canadian Arctic Archipelago were B. glabella var. purpurascens of wide distribution in the High Arctic, B. glabella var. glabella of wide distribution in the Arctic and subarctic and alpine regions, B. glabella var. prostrata, endemic to northern Ellesmere Island, B. pilosa, an endemic restricted to the coast of continental North America near Cape Bathurst, B. thorild-wulffii var. thorild-wulffii, an endemic of Greenland and the northern Canadian Arctic Archipelago, and B. thorild-wulffii var. glabrata of Banks and Victoria Islands, B. humilis var. ellesmerensis, an endemic of northern Ellesmere Island, var. humilis widely distributed on calcareous soils in northern North America. Harris's varieties have not been formally proposed.
Rollins (1993) applied a much wider species concept of the genus than was done in the Panarctic Flora Checklist (Petrovsky, in Elven et al. 2003). His B. glabella included as synonyms B. purpurascens and B. bartlettiana; his B. humilis included as synonyms B. novae-angliae and B. richardsonii (B. intermedia was not mentioned in his treatment). He thereby accepted only four species from arctic America (excluding Greenland): B. glabella, B. humilis, B. pilosa and B. thorild-wulffii. Elven et al. (2003) considered Rollins' treatment too inclusive, as his concept of B. glabella included the majority of the North American, Greenlandic, and Northern European variation.
Phytogeography Harris (1985) noted that the present discontinuous distribution of Braya species suggested that in pre-Pleistocene times they, or their ancestors, had a much more continuous distribution across northern North America. Glaciation may have removed Braya from much of its former range, and the genus has been only partially successful in recolonising these areas in postglacial times. Part of this lack of success has likely been due to the absence of long distance dispersal mechanisms in Braya, but by far the most important factor may have been the glacial eradication of the edaphic conditions required by the genus from a large portion of its former range. Members of the genus are almost entirely, if not entirely, restricted to calcareous soils.
Warwick et al. (2004) discussed the phylogeny of Braya and Neotorularia (Brassicaceae) based on nuclear ribosomal internal transcribed spacer and chloroplast trnL intron sequences and concluded that on DNA evidence the genus Neotorularia should be re-included in Braya.
Illustrations. • Genus Braya. Genus with a tufted habit, simple, linear or narrowly spatulate, purple-tinged, entire leaves, and small white or lilac flowers in head-like inflorescences.
This publication is available on the internet (posted May 2011) and on CD-ROM (published in 2007). These versions are identical in content, except that the errata page for CD-ROM is accessible on the main index page of the web version.
Recommended citation for the web-based version of this publication: Aiken, S.G., Dallwitz, M.J., Consaul, L.L., McJannet, C.L., Boles, R.L., Argus, G.W., Gillett, J.M., Scott, P.J., Elven, R., LeBlanc, M.C., Gillespie, L.J., Brysting, A.K., Solstad, H., and Harris, J.G. 2007. Flora of the Canadian Arctic Archipelago: Descriptions, Illustrations, Identification, and Information Retrieval. NRC Research Press, National Research Council of Canada, Ottawa. http://nature.ca/aaflora/data, accessed on DATE.
Recommended citation for the CD-ROM version of this publication: Aiken, S.G., Dallwitz, M.J., Consaul, L.L., McJannet, C.L., Boles, R.L., Argus, G.W., Gillett, J.M., Scott, P.J., Elven, R., LeBlanc, M.C., Gillespie, L.J., Brysting, A.K., Solstad, H., and Harris, J.G. 2007. Flora of the Canadian Arctic Archipelago: Descriptions, Illustrations, Identification, and Information Retrieval. [CD-ROM] NRC Research Press, National Research Council of Canada, Ottawa..