Flora of the Canadian Arctic Archipelago
Brassicaceae (Cruciferae), Draba family.
Published in Sp. Pl. 642. 1753.
Vegetative morphology. Plants 1–15(–40) cm high; perennial herbs (Arctic Island species); caespitose (usually), or not caespitose. Taproot present. Ground level or underground stems horizontal (between rosettes), or vertical, or absent; rhizomatous, or stoloniferous; elongate, or compact (larger plants); 1–1.5 mm wide. Caudex present (variously developed). Aerial stems erect. Aerial stem trichomes spreading, or erect. Leaves mainly basal, or distributed along the stems, or basal in a rosette; alternate, or whorled; dying annually and non-persistent, or marcescent. Petioles absent. Leaf blades simple. Leaf blade bases truncate, or cuneate, or attenuate. Blades 2–20(–50) mm long, 0.6–5(–12) mm wide, appressed to the stem or spreading, linear or oblong or lanceolate or ovate or oblanceolate or obovate or spatulate, flat, veins reticulate or appearing single-veined or with inconspicuous veins, midvein conspicuously larger than the lateral veins (Draba corymbosa). Blade adaxial surface glabrous or glabrescent or scabrous or hairy, hairs woolly (D. aurea, D. oligosperma), hairs simple or branched or stellate, hairs sparse or moderately dense or dense, hairs white, or translucent. Blade abaxial surface glabrous or glabrescent or hairy, hairs pilose or villous or tomentose or woolly, hairs sparse or moderately dense or very dense, hairs white, hairs straight or curved or irregularly branched or stellate, hairs appressed or spreading or erect. Blade margins entire or dentate, with non-glandular hairs (usually) or glabrous; apices acute (usually), or obtuse.
Reproductive morphology. Flowering stems with leaves, or without leaves. Flowering stems hairy. Flowering stems villous, or tomentose, or woolly. Flowering stem hairs simple, or branched, or stellate; shorter than the diameter of the flowering stem, or longer than the diameter of the flowering stem; white or translucent. Inflorescences racemose, or cymose, or head-like; dense, or diffuse; linear, or oblong, or lanceolate, or ovate, or globose or sub-globose; (0.5–)1–10(–30) cm long; 4–15(–50) mm wide; elongating as the fruit matures, or not elongating as the fruit matures. Pedicels glabrous, or with non-glandular hairs. Flowers per inflorescence 2–12(–30); small, or medium-sized. Sepals conventional; 4; free; 0.5–2(–2.2) mm long; 1.3–2.5(–3) mm wide; green, or yellow, or brown, or purple, or purplish red; herbaceous, or scarious. Calyx glabrous, or hairy. Calyx hairs pilose, or villous (if applicable); non-glandular; white or translucent. Petals conventional; free; 4; white, or yellow; ovate, or obovate, or oblanceolate, or spatulate, or obtriangular; unlobed, or slightly lobed or undulating; (1.8–)2–6 mm long; (0.7–)1–4 mm wide. Stamens 6; stamen filaments markedly unequal in length; stamen filaments glabrous. Anthers reddish, becoming yellow, or yellow; ellipsoid, or short-cylindrical, or ovoid, or sub-globose, or triangular; 0.2–0.9 mm long. Ovary superior; carpels 2; syncarpous. Ovaries ovate, or inverse turnip-shaped, or oblong, or sub-globose; glabrous, or hairy; pubescent, or tomentose, or woolly. Ovary hairs sparse, or very dense; white; appressed, or spreading; straight, or wavy, or branched, or stellate. Styles 1; completely fused; thick and short; (0.05–)2–6(–8) mm long; straight. Stigmas per ovary 1(–2). Placentation parietal. Ovules per ovary (8–)12–28(–44). Fruit stalked; stalk (1–)2–12(–20) mm long; dry; a silique; spherical, or ellipsoid, or ovoid, or elongate-cylindrical, or obovate, or oblong, or broadly lanceolate, or lanceolate; brown, or red, or blue, or green at maturity, or yellowish; (3–)4–12.5 mm long; (1.2–)2–3.5(–4.5) mm wide; glabrous, or hairy, or glabrescent; surface venation reticulate, or appearing veinless; distinctly flattened; dehiscent; shedding the outer walls to expose a thin inner wall, with the seeds attached at the margins on either side. Styles persisting in fruit (0.05–)0.1–0.8 mm long. Seeds (8–)12–28(–44); (0.4–)0.8–1.5 mm long; brown, or yellowish; surfaces smooth, verrucose, rugose.
Chromosome information. 2n = 16, or 32, or 40, or 48, or 56, or 64, or 80, or 100–144.
Ploidy levels recorded 2x-18x.
Ecology and habitat. Substrates: wet meadows, hummocks, snow patches, around the margins of ponds, depressions of low-centre polygons, along streams, river terraces, lakeshores, tundra, slopes, ridges, cliffs, seashores, dry meadows, barrens, flood plains; imperfectly drained moist areas, seepage slopes, dry, moderately well-drained areas; rocks, gravel, sand, silt, clay, till, moss; with low organic content, with high organic content, peat; acidic, or calcareous, or nitrophilous, or non-calcareous, or circum-neutral.
General notes. The genus Draba is well known for its taxonomic complexity in arctic and alpine floras, and the polyploids in particular present vexing taxonomic problems (Brochmann et al. 1992a-d, 1993). It has been suggested that polyploids in Draba may have formed recurrently from different populations of the parental species (polytopy), and it is also possible that a given taxonomic species may actually comprise several polypoid races, each originating from different progenitor species.
Brochmann et al. (1992a) investigated three morphologically variable Nordic species and their possible progenitors, using enzyme electrophoresis and restriction site analysis of chloroplast DNA (cDNA) and nuclear ribosomal RNA (rDNA) genes, and found the electrophoretic data showed high levels of fixed heterozygosity in the three polyploids, showing that they are all genetic alloploids. Brochmann (1992a-b) studied pollen and seed morphology of Nordic Draba from 54 populations representing 15 species and found pollen size was strongly correlated with chromosome number, but was unreliable for inferring the exact choromsome ploidy level of individual populations. Brochmann et al. (1992d), in a study of gene flow across ploidy levels in Draba, found that interspecific hybridisation across ploidy levels in the genus may result in re-establishment of fertility and probably of euploid chromosome numbers, suggesting that the taxonomic complexity in Draba is also contributed to by the recurrent formation of allopolyploids. Brochmann et al. (1993) investigated 101 populations of Nordic Draba in 16 species and found discrepancies between genetic and taxonomic relationships in the taxa. The relationships inferred from the crossing data largely agreed with those inferred from previously published molecular data, but corresponded poorly to relationship inferred from morphology. Brochmann (1993) investigated reproductive strategies of 132 diploid and polyploid populations of arctic Draba (2x-16x) to clarify possible relationships between reproductive strategies and polyploid evolution in the genus. Koch and Al-Shehbaz (2002) reported that molecular data indicate complex intra- and intercontinental differentiation of American Draba.
The Draba treatment presented here is provisional. Much addtional study is needed to sort out the taxonomic complexity of the genus in arctic North America.
Illustrations. • Adjacent species. Three species of Draba growing adjacent on a calcareous rocky slope. Nunavut, Cornwallis Island, Resolute Bay, adjacent to the original hamlet "dump". Aiken. CAN. • Fruit. Genus and family characterised by siliques: fruits that have a partition with seeds attached to the edges of the partition and not to the ovary wall.
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..