Astragalus eucosmus B.L. Rob.
Elegant milk-vetch.
Fabaceae (Leguminosae), pea family.
Rhodora 10: 33. 1908.
Based on Astragalus oroboides var. americanus Gray, Proc. Amer. Acad. 6: 204. 1864 (non A. americanus (Hooker) Jones, 1898). Based in turn on Phaca elegans Hooker, Fl. Bor. Amer. 1: 144. 1831. Astragalus elegans (Hooker) Sheldon., Minn. Bot. Stud. 1: 154. 1894, non Bunge (1869). Atelophragma elegans (Hooker) Rydb., Bull. Torr. Bot. Club 32: 660. 1905.
Type: "Prairies of the Rocky Mountains ... Drummond." Holotype: K.
Atelophragma atratum Rydb. n. Amer. Fl. 24: 372. 1929. "Type collected August 22, 1896, on Herchel Island, Yukon, Alvin Seale". Holotype DS. Non Astragalus atratus Wats., 1871. Astragalus sealei Lepage, Naturalisteastern Canadaad. 85: 102, fig. z. 1958. Astragalus eucosmus subsp. sealei (Lepage) Hultén, Arkiv för Botanik, Andra Serien. 7: 77. 1968.
For further synonymy see Barneby (1964).
Vegetative morphology. Plants perennial herbs; 10–30 cm high; with basal leaves or spreading stems. Taproot present. Caudex present. Aerial stems decumbent (to ascending with slender branches); glabrous (older stems), or sparsely hairy. Leaves distributed along the stems; alternate; compound; marcescent. Stipules present; scale-like (with age), or leaf-like (younger leaves); sheathing, or not sheathing; brown, or green. Petioles 5–20 mm long. Blades 25–40 mm long; 15–25 mm wide. Blades veins pinnate. Blades adaxial surface glabrous. Blades abaxial surface glabrous (seen at 10X), or hairy (densely hairy, with white or black hairs). Blades abaxial surface hairs sparse, or moderately dense. Blades abaxial surface hairs short-silky, or strigose. Blades abaxial surface hairs white, or translucent hairs; straight; appressed. Leaflet arrangement pinnate. Leaflets 8–17; 5–12 mm long; linear, or oblong (lateral veins often obscure).
Reproductive morphology. Flowering stems present. Flowering stems without leaves; hairy (hairs black, transparent, or black with transparent tips). Inflorescence racemose; 1.5–5 cm long (dense in bud in the Arctic Islands but elongating to as much as 19 cm further south); elongating as the fruit matures. Flowers per inflorescence 6–16; medium-sized, 5–15 mm in diameter or length; zygomorphic. Calyx sepals 5; fused. Calyx brown, or black (because of black hairs); tubular; 5-lobed; hairy (densely). Petals both free and fused; longer than the calyx; 5; purple (dark); with contrasting markings (veins prominent); unlobed (4 petals), or shallowly lobed (banner petal); 6.5–7.5 mm long. Corolla papilionaceous. Corolla keel blunt. Stamens 10; filaments all equal in length (slightly unequal). Nectaries present. Gynoecia superior. Carpels monomerous (stipitate). Stipes 0–0.4 mm long (in fruit). Stigmas per style 1. Ovules 3–8. Fruit stalked. Fruit with calyx persisting; dry; a legume (pendulous); spherical (almost), or ellipsoid, or ovoid (or cuneate after pressing; not inflated); dehiscent. Fruit 5–13 mm long; 2.5–5.5 mm wide; black, or brown; hairy (with white and black hairs). Legume nearly 2-locular by intrusion of placenta. Styles may persist until dehiscence but are not modified. Seeds 3–8; 1–2 mm long (i.e., the longest dimension); yellowish; with surfaces smooth.
Chromosome information. 2n = 32. 32 (4x). - Ledingham (1957, 1960); Ledingham and Fahselt (1964 Alaska); Johnson and Packer (1968 northwestern Alaska ); Dawe and Murray (1979 Alaska); Löve and Löve (1982a central Canada). Ploidy levels recorded 4x.
Distribution. Northern hemisphere distribution: North American. Low arctic. Rare (known from Apex, Iqaluit, and Kimmirut). Arctic Islands: Baffin.
Ecology and habitat. Substrates: river terraces, slopes, ridges, seashores; moderately well drained areas; calcareous (growing in sand, gravel, and with grasses at Iqaluit; plants growing as a sand binder on the beach at Apex, In continental North America plants of this species often grow among willows on sand and gravel bars in rivers and by sheltered lake shores); gravel, sand, till. Habitats: plants flower and fruit abundantly.
Taxon as an environmental indicator. Plants vary in height from 10 cm tall in severe environments to 30 cm tall under ideal growing conditions. The northernmost record that Polunin (1940) found was Great Bear Lake approx. 66°N. Since 1940, this species has been collected further north, at the Mackenzie Delta, 68°55'N. On the arctic islands, this species grows north to Iqaluit, 63°45'N.
Notes. Barneby (1964) recognized this taxon as being in section
Oroboidei. A similar species, A. robbinsii (Oakes) Gray grows in
central and southern Yukon and southern Alaska. Barneby (1964) stated "the
elegant milk-vetch, A. eucosmus, is closely related to A.
robbinsii differing chiefly in the sessile pod. The leaflets tend to be
narrower and the flowers are often smaller, but neither of these features is
diagnostic of A. eucosmus and fruits at least half formed are often
necessary for identification....
"Despite its great range, A.
eucosmus is only moderately variable, much less so than a glance at the
synonymy might suggest. Normally an erect plant of moderate stature, it is
susceptible to dwarfing in open montane and far northern environments, where the
stems become diffuse or weakly ascending as well as shorter, and the raceme
tends to become shorter and more compact in fruit. ...
"The raceme of A.
eucosmus ordinarily elongates rapidly during anthesis, the axis becoming
about 3.5–19 cm long in fruit with pods well spaced along its length.
Instances of shortening ... are correlated with short diffuse stems and an
unfavorable habitat, mostly on exposed seashores at high latitudes in eastern
Canada and Baffin.".
Illustrations. • Plant in habitat. Plants growing on rocky ridge, Nunavut, Baffin Island, Iqaluit, 26 July 1982, J.M. Gillett 19055. CAN. • Plant in habitat. Plant with prostrate stems. Nunavut, Baffin Island, Iqaluit. Aiken 02–064. • Close-up of inflorescence with purple flowers. Inflorescence with purple flowers that have silver grey, hairy sepals. Nunavut, Baffin Island, Iqaluit, 26 July 1982, J.M. Gillett 19055. CAN. • Close-up of fruiting stem. Ovoid, hairy fruiting pods developing. Nunavut, Baffin Island, Iqaluit. Aiken 02–064. • 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).
