Draba lactea Adams
Brassicaceae (Cruciferae), Draba family.
Mem. Soc. Imp. Naturalist Moscou 5: 104. 1817
Draba allenii Fernald
Draba wahlenbergii Hartman var.
heterotricha Lindblad
Draba fladnizensis Wulfen var.
heterotricha (Lindblad) Ball
Type: The diagnosis of D. lactea Adams fits with two of the available original specimens but not with the third. The specimens may well be from two species. The name should be typified by one of the specimens (in LE or MW) fitting the diagnosis. Thereby it becomes a synonym of the diploid D. fladnizensis. The hexaploid which until now has gone by the name D. 'lactea' needs another name and the oldest available is D. wahlenbergii Hartm. with available material (original Wahlenberg material in UPS) for unambiguous typification.
Vegetative morphology. Plants perennial herbs; 6–15 cm high; not caespitose; dwarf, forming small loose mats, from ground level or under ground stems with many branches close together). Taproot present. Caudex present. Aerial stems erect; glabrous, or sparsely hairy (glabrous or with forked trichomes on base). Leaves basal in a rosette (very rarely with a single cauline leaf); alternate; simple; existing for a single season or less. Petioles absent. Leaf blade bases attenuate. Blades 8–10 mm long; 1.5–2.5 mm wide. Blades herbaceous; oblanceolate; appearing single-veined. Blades adaxial surface glabrescent. Blades adaxial surface hairs stellate and branched; sparse; white and translucent. Blades abaxial surface not glaucous; glabrescent. Blades abaxial surface hairs sparse; white, or translucent hairs. Blade margins not lobed. Blade margins entire; with non-glandular hairs. Conspicuous hydathodes absent. Leaf apices acute.
Reproductive morphology. Flowering stems present. Flowering stems conspicuously taller than the leaves; without leaves; hairy. Inflorescence racemose. Pedicels present. Flowers per inflorescence 3–6; small, less than 5 mm in diameter or length; actinomorphic. Calyx sepals 4; free; 2–2.5 mm long. Calyx green and purple; herbaceous; glabrous. Petals free; longer than the calyx; 4; white; without contrasting markings; obovate; unlobed, or shallowly lobed; 3–4 mm long. Flowers bisexual. Stamens 6; filaments markedly unequal in length; free of the corolla; filaments glabrous. Anthers yellow; 0.2–0.3 mm long. Gynoecia superior. Carpels syncarpous; 2. Ovaries glabrous. Styles 1; 0.2–0.3 mm long. Stigmas per style 1. Placentation parietal. Ovules 8–12. Fruit stalk 3–5 mm long. Fruit without calyx persisting; dry; a silique; ovoid; distinctly flattened; dehiscent. Fruit 6–10 mm long; 2.5–3 mm wide; purple and green at maturity; glabrous. Styles remaining straight; persisting in fruit 0.1–0.5 mm long. Seeds 8–12; 1–1.2 mm long; brown; with surfaces verrucose.
Chromosome information. 2n = 32 and 48. 32 (4x).
- Zhukova and Tikhonova (1971 Chuk, as D. pseudopilosa); Zhukova and
Petrovsky (1984 north eastern Asia, as D. fladnizensis and D.
pseudopilosa); Grundt (unpubl. western Alaska,Greenland, tetraploid in
cytometry).
48 (6x). - Jørgensen et al. (1958
Greenland); Böcher (1966a Greenland and Svalbard); Knaben (1966c Norway);
Knaben and Engelskjøn (1967 Norway); Zhukova (1968 north eastern Asia, as
D. pseudopilosa); Zhukova and Tikhonova (1971, 1973 north eastern Asia,
as D. pseudopilosa); Zhukova et al. (1973 north and northerastern Asia,
as D. pseudopilosa); Mulligan (1974 Ala, two counts, northern Canada,
seven counts); Packer and McPherson (1974 northern Alaska); Engelskjøn
(1979 northern Norway); Löve and Löve (1982 arctic Canada); Zhukova
and Petrovsky (1980 western Chukotka, as D. pseudopilosa, 1984 western
Chukotka, as D. lactea and D. pseudopilosa); Brochmann et al.
(1993 Svalbard); Grundt (unpubl. Ala, Canada, Greenland, Svalbard, Norway,
Siberia, hexaploid in cytometry). Ploidy levels recorded 4X&6x.
Distribution. Northern hemisphere distribution: circumpolar; Greenland, Canada, Eurasia. Yukon, Northwest Territories Islands, Continental Northwest Territories, Nunavut Islands, Continental Nunavut, Northern Québec. Arctic, or alpine. Range in the Canadian Arctic Archipelago widespread. Common. Arctic Islands: Baffin, Devon, Ellesmere, Axel Heiberg, Parry Islands (Bathurst and Prince Patrick), Cornwallis, Banks, Victoria, Prince of Wales, Somerset, King William, Southampton (Prince Charles Island, Ellef Ringnes Island, and Jenny Lind Islands).
Ecology and habitat. Substrates: wet meadows, hummocks, around the margins of ponds, along streams, river terraces, lake shores, slopes, ridges, cliffs; imperfectly drained moist areas (seepage swales), or on seepage slopes, or dry; acidic, or calcareous; rocks, gravel, sand, silt, clay, till, moss; with low organic content, or with high organic content, or peat.
Notes. Brochmann et al. (1992) investigated this species as one of
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 heterzygosity in the three polyploids showing that
they are all genetic alloploids. Electrophoretic and rDNA data suggest that
D. lactea is a polyphyletic polyploid and likely to have formed numerous
times in different areas.
Brochmann (1992) in a study of and seed morphology
of Nordic Draba found two populatons of D. lactea that had
conspicuously different exine sculpturing that further supported the hypothesis
that this hexaploid is polyphyletic and has been derived from various
combinations of diploid species.
Draba lactea is known as hexaploid,
2n=48, but some deviating counts have been reported, e.g. 2n=32 from Siberia and
the Russian Far East (Zhukova et al. 1973) and 2n=16 from Alaska (Dawe and
Murray 1981). Investigations made on individuals collected from the latter
locality in Alaska (Grundt et al. in prep.) have shown that they represent a
D. nivalis variety var. candida described by Schultz (1927) and
also recognised by Hitchcock (1941). The name D. lactea is furthermore
probably not correct, but may represent a synonym of D. fladnizensis. The
correct name may be D. wahlenbergii, but this work has not yet been
completed. The species is large-flowered with white petals. In the Nordic view
this species is said to have stellate hairs towards the tip on the lowermost
side of the rosette leaves, but the indumentum shows a much larger degree of
variation when considering a larger geographical area. Firstly, the hairs are
not stellate, but rather dendrittic and irregular. Secondly, some individuals
have this hair type all over the leaf, others hardly at all. [A new species from
Greenland, Draba böcheri Gjærevoll and Ryvarden was described
in 1977 (Gjærevoll and Ryvarden), but probably represents part of the
normal lactea variation]. Populations collected from Alaska with
tetraploid counts have been found to cluster together with hexaploid
lactea populations in a UPGMA analysis based on RAPDs (Random Amplified
Polymorphic DNAs; Grundt et al. in prep.). There is reason to believe that
tetraploid and hexaploid populations contain the same diploid ancestor genomes,
and that the hexaploid populations simply have an extra copy of one of them.
Thus, both should be contained within the same species (Grundt personal
communication 2001)
Grundt (mainly unpubl. yet) has available genetical data
that indicate that the hexa- (and tetra-)ploid D. wahlenbergii
(lactea auct.) are less polyphyletic than previously assumed, that its
parentage probably is from the diploids D. subcapitata and D.
palanderiana or their predessors, and that its origin might be Beringian
(broadly spoken). This is rather opposite to the original (Knaben and Brochmann)
hypothesis of an origin from D. fladnizensis and D. nivalis.
Illustrations. • Close-up of flowering plant. Plant growing in moss mats, a comparatively moist habitat for plants in the "fladnizensis group". Note the comparatively large white flowers, i.e. 3–5 mm long petals vs. 2–3 in the other taxa in the group. The flowering stems are leafless and glabrous, but can occasionally be somewhat pubescent at the base. Note that the emerging siliques are glabrous, and that the lowermost surface of the leaves have stellate hairs. The amount of stellate hairs on the leaf surface varies in this species. Photographed by Hanne H. Grundt at Svalbard in 1997. No voucher. • Fruiting plant. A fruiting plant with narrowly elliptic and glabrous siliques. Note that the rosette leaves of this specimen are grayish coloured due to a dense coverage of stellate hairs. The amount of stellate hairs on the rosette leaves is highly variable in this species. Collected/photo- graphed by Hanne H. Grundt, coll. 28, 1998, Alaska, Seward Peninsula. Voucher in O. • Close-up of plant. Drawing by Mrs S. Bergh and Mrs L. Barstad based on a collection from Svalbard, Oscar II Land, Kapp Boheman, 1 km aust for signalet [1 km E. of cairn]. 30 Aug. 1924. J. Lid. (eller: Kapp Boheman, vik inn for ytste neset. 30 Aug. 1924. J. Loid (as D. wahlenbergii). 0 209747). O 209724 (SJEKK HERB) With permission of the Botanical Museum University of Oslo, Norway. • Arctic Island Distribution.
Cite this publication as: ‘S.G. Aiken, M.J. Dallwitz, L.L. Consaul, C.L. McJannet, L.J. Gillespie, R.L. Boles, G.W. Argus, J.M. Gillett, P.J. Scott, R. Elven, M.C. LeBlanc, A.K. Brysting and H. Solstad. 1999 onwards. Flora of the Canadian Arctic Archipelago: Descriptions, Illustrations, Identification, and Information Retrieval. Version: 29th April 2003. http://www.mun.ca/biology/delta/arcticf/’. Dallwitz (1980) and Dallwitz, Paine and Zurcher (1993, 1995, 2000) should also be cited (see References).
