Flora of the Canadian Arctic Archipelago
English: Purple rockcress,
French: Braya glabre,
Brassicaceae (Cruciferae), Draba family.
Published in In Franklin, Narr. Journey Polar Sea (Bot. App.) 743. 1823.
Type: Canada: Northwest Territory, Copper Mountains, leg. Richardson. Holotype: BM.
Synonymy. Braya alpina Sternberg and Hoppe var. glabella (Richardson) Watson, Bibliogr. Index N. Amer. Bot. 51. 1878.
Braya americana (Hooker) Fernald, Rhodora 23: 203. 1926. In part.
Braya bartlettiana Jordal, Rhodora 54: 36. 1952.
Braya bartlettiana Jordal var. vestita Hultén, Ark. Bot. 7, 1, p. 66. 1968a.
Braya aenea Bunge subsp. pseudoaenea V.V. Petrovsky, in Tolm., Fl. Arct. URSS 7: 49. 1975.
Vegetative morphology. Plants 4.7–20(–22.7) cm high; perennial herbs; caespitose. Taproot present (tapering from the caudex). Ground level or underground stems vertical. Caudex present (stout and freely branching, compact or elongate). 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 (usually, decumbent or prostrate rarely (Harris 1988). Aerial stem trichomes spreading. Leaves mainly basal (older plants), or basal in a rosette; patent, or erect (somewhat spreading); alternate; dying annually and non-persistent. Petioles present, or absent; 0–40 mm long (40 mm long, CAN 64174); winged (at the point of attachment), or not winged; glabrous, or hairy; pilose (sparsely). Petiole hairs longer than the diameter of the petiole; spreading. Leaf blades simple. Leaf blade bases attenuate. Leaves not grass-like. Blades (4–)8–60(–79) mm long (to 79 mm (Harris 1988)), (0.3–)0.6–4(–6) mm wide, spreading (somewhat fleshy, green to deep purple), linear or spatulate (broadly to oblanceolate), appearing single-veined or with inconspicuous veins. Blade adaxial surface dull, without sessile glands, glabrous or glabrescent or hairy, hairs pubescent or pilose (if applicable), hairs simple or branched (bifid or trifid), hairs sparse or moderately dense, hairs white, or translucent. Blade abaxial surface glabrous or glabrescent or hairy, hairs pilose (if applicable), hairs sparse or moderately dense, hairs white, hairs curved (or forked), hairs appressed or spreading. Blade margins entire or dentate (sometimes with 1–2 teeth per side), with non-glandular hairs, with 1–2 teeth on each side of the blade; apices obtuse (often with a tuft of long simple trichomes).
Reproductive morphology. Flowering stems with leaves (occasionally, but then only one leaf), or without leaves (or with a single leaf or leafy bract subtending the lowermost flower or fruit, often purple or purple tinged). Flowering stems hairy. Flowering stems pilose. Flowering stem hairs simple, or branched (bifid or trifid); 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; with non-glandular hairs. Flowers per inflorescence (3–)4–10(–12); small. Sepals conventional; 4; free; (0.7–)1–2 mm long; (1.6–)1.9–3.7 mm wide; green, or purple (tinged). Calyx hairy (usually), or glabrous (occasionally). Calyx hairs pilose; white or translucent. Calyx margins ciliate (sometimes, as a tuft of hairs at the tip). Petals conventional; free; 4; white, or purple (tinged, especially towards the base); without contrasting markings; obovate (abruptly narrowed from blade to claw), or spatulate (weakly or strongly so); unlobed; (2.1–)2.4–4.5(–4.7) mm long; (0.75–)1–3(–3.2) mm wide. Stamens 6; stamen filaments markedly unequal in length; stamen filaments glabrous. Anthers yellow; sub-globose; 0.4–0.5 mm long. Ovary superior; carpels 2; syncarpous. Ovaries oblong; hairy; pilose. Ovary hairs very dense; white; spreading; straight, or wavy, or branched (2-forked). Styles present; 1; completely fused; thick and short; 0.5–1.5 mm long. Stigmas per ovary 1. Placentation parietal. Ovules per ovary (10–)16–20. Fruit stalked; stalk 2–5(–8) mm long; dry; a silique; ellipsoid to ovoid, or oblong, or lanceolate (terete, somewhat torulose or not at all, often curved); purple and green at maturity, or purple; (3–)5–12.5(–15) mm long; (0.8–)1.1–3(–3.6) mm wide; hairy (hairs simple, bifucate, or occasionally trifurcate); surface venation ribbed (longitudinally with faint veins); not 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 (0.35–)0.5–1.6(–2) mm long. Seeds (10–)16–20; 1.1–1.4 mm long; brown, or yellowish; surfaces smooth, rugose (at 40×).
Chromosome information. 2n = 28, or 56, or 64.
2n (4x) = 28. Dawe and Murray, in Löve (1979, Alaska?); Zhukova and Petrovsky (1981, Wrangel Island, 1984, eastern Chukotka, both as B. aenea subsp. pseudoaenea);
2n (8x) = 56. Dawe and Murray, in Löve (1979, Alaska?); Harris (1985, several counts from arctic, subarctic, and alpine North America); Zhukova and Petrovsky (1984, eastern Chukotka, as B. aenea subsp. pseudoaenea); Murray and Kelso (1997, western Alaska). Additional counts Mulligan (2003), but some specimens annotated as B. glabella by Mulligan may have been considered B. purpurascens in this treatment after a survey of specimens at DAO by Elven, May 2003.
2n (8x) = 64. Dawe and Murray, in Löve (1979, Alaska?).
Ploidy levels recorded 4x/8x.
Ecology and habitat. Substrates: imperfectly drained moist areas (wet places in the tundra (CAN 259236), dry (CAN 273776)); rocks, gravel, sand; calcareous. Barren calcareous soils and gravels on lake and sea shores, gravel bars, scree slopes, solifluction lobes and disturbed sites; flat, poorly drained, sparsely vegetated, calcareous tundra (CAN 368119).
North American distribution. Alaska, Yukon, Northwest Territories Islands, continental Northwest Territories, Nunavut Islands, continental Nunavut, northern Quebec. Range in the Canadian Arctic Archipelago limited. Uncommon. Low Arctic (southern most islands of the Canadian Arctic Archipelago south through the Mackenzie and Rocky Mountains to Colorado, west to Seward Peninsula, Alaska, east to Hudson Bay). Arctic islands: Cornwallis, Banks (south-west).
Northern hemisphere distribution. Amphi-Beringian, or North American. Wrangel Island, East Chukotka, West Alaska, North Alaska Yukon, Central Canada, West Greenland (?), East Greenland (?).
General notes. Harris (1985) considered B. glabella to be a wide-ranging species composed of many isolated, inbreeding, and somewhat distinct populations. He considered that none of these populations could be consistently grouped into subgroups distinctive enough to warrant taxonomic recognition at the species level, so it seemed wisest, and certainly most practical, to recognise a single polymorphic species.
Recent DNA sequence data provide strong evidence that Braya glabella is an allopolyploid that includes genomic contributions from both the B. pilosa/B. thorild-wulffii and the B. humilis/B. linearis/B. alpina lineages. Perhaps it has arisen several times in several different places, as has been demonstrated in some allopolyploid Draba species.
Braya glabella is extremely variable throughout its range. Multiple origins and non-uniform genomic contributions from parental lineages could account for the morphological variability in B. glabella. Local pockets of variation have at times been recognised at the species, subspecies, and variety levels, but most of these taxonomic designations break down when the complex patterns of variation from the entire range of B. glabella are considered. However, populations of B. glabella from High Arctic regions are usually distinguishable from those from lower arctic and subarctic montane populations, and they are recognised here as subsp. purpurascens and subsp. glabella, respectively. Some populations on southern islands in the Canadian Arctic Archipelago and along the northern coast of continental North America will defy unequivocal placement.
Key to subspecies.
1a.Fruits oblong to narrowly oblong-lanceolate, 3.5–8.3 times longer than broad; mature fruiting inflorescences often loosely elongated; plants of lower arctic, subarctic, and montane distribution....subsp. glabella
1b.Fruits ovoid-ellipsoid to oblong-ellipsoid (rarely broadly oblong-lanceolate), 2.5–3.7 times longer than broad; mature fruiting inflorescences often densely compact; plants mostly of High Arctic distribution, south to the northern coast of continental North America...subsp. purpurascens
Harris (1985) noted that Braya glabella Richards. is perhaps the most poorly understood Braya species. It is extremely variable from one population to another, and to some extent, even within populations. Previous authors have split the species into several taxa on the basis of differences in silique shape and pubescence, style length, stigma breadth and lobing, leaf shape and dentation, and inflorescence length. While it is true that many populations of B. glabella appear to be strikingly distinct on the basis of these attributes, when a large number of specimens are examined from throughout the entire range of distribution the perceived morphological gaps quickly blur into a bewildering array of overlapping forms. Richardson's original collections of Braya glabella and the original collections of Brown's Platypetalum purpurascens happen to fall near the opposite edges of the spectrum of diversity in the species. It is not at all surprising that Brown (1823, 1824), as well as the overwhelming majority of subsequent authors, recognised the two taxa as separate and distinct species; indeed, the type specimens of B. glabella and P. purpurascens appear to be very different. But, when the entire range of variation is observed, the two morphological forms flow together to the point that it is impossible to draw a sharp boundary line between them. Abbe (1948) commented on the range of variation to be found in this group even within a single population. He and his wife collected 58 individuals from a population at Richmond (E.C. and L.B. Abbe 3819) and found that the plants ranged from specimens that fell very nicely within the range of variation of "typical" Braya purpurascens as described by Brown (1823) and illustrated by Hooker (1830, Tab. XXIII) "...into the robust type of specimen from Southampton Island..." Had Abbe had access to authentic fruiting material of B. glabella, he almost certainly would have realised that the robust specimens from Southampton Island (for example, Malte 120677) are near perfect matches for "typical" B. glabella. This, in fact, appears to be the pattern in the group; specimens from the North American High Arctic are more or less B. purpurascens-like, and plants from lower arctic, subarctic, and montane regions are generally more B. glabella-like, but it is almost always possible to find plants in any population that look somewhat out of place and approach, morphologically, plants of the alternate morphological form. The populations on and near the northern coast of continental North America appear to be in the zone of overlap, and it is here that the greatest difficulty is encountered in attempting to segregate specimens into one or the other of the two forms. This is especially true in disturbed areas, where normally inbreeding, isolated populations come together as they move onto the newly available habitats, gene flow again begins to take place, and plants from the same population may exhibit an extreme range of diversity. On the basis of morphological and molecular evidence, it is difficult to justify the recognition of more than one species in this very plastic group, but it does seem desirable to divide the species into two rather weak subspecies. Many populations will be readily separable into one of these subspecies, but other populations will undoubtedly defy unequivocal placement, particularly those from areas where the ranges of the subspecies meet. Harris (1985) also noted that Abbe (1948), even with very limited material to work with, realised the close relationship between Braya glabella and B. purpurascens and became suspicious that the two might comprise a single species: "There is no evidence against Braya glabella of Richardson being conspecific with B. purpurascens (R. Brown) Bunge. The chief difficulty is the lack of positive evidence concerning the nature of the mature siliques and of their arrangement on the scape. Should these support the possibility that the two are conspecific, then the name B. glabella would have to be substituted for B. purpurascens." It appears that B. glabella and B. purpurascens are indeed conspecific and warrant recognition only at the infraspecific level. Because the epithet "glabella" (Richardson 1823) was validly published before the epithet "purpurascens" (Brown1823), B. glabella has nomenclatural priority over B. purpurascens.
Illustrations. • Close-up of plant. Drawing by Mrs. S. Bergh and Mrs. L. Barstad based on a collection from Svalbard, Dickson Land, Lyckholmsflyan. 8 August, 1924. J. Lid. O 200079. With permission of the Botanical Museum, University of Oslo, Norway. • Close-up of flower and fruiting body. Fruit more than 3x as long as wide. Drawing by Mrs. S. Bergh and Mrs. L. Barstad based on a collection from Svalbard, Dickson Land, Lyckholmsflyan. 8 August, 1924. J. Lid. O 200079. With permission of the Botanical Museum, University of Oslo, Norway. • Arctic Island Distribution.
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..