Astragalus racemosus Pursh var. racemosus
-
Authors
Rupert C. Barneby
-
Authority
Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(1): 1-596.
-
Family
Fabaceae
-
Scientific Name
-
Type
"In Upper Louisiana. Bradbury."—Holotypus, labeled "Louisiana, Bradbury. Pursh’s specimens," PH! isotypus, dated 1811-12, BM!
-
Synonyms
Astragalus galegoides Nutt., Tragacantha racemosa (Pursh) Kuntze, Tium racemosum (Pursh) Rydb., Astragalus racemosus var. typicus Ced.Porter, Astragalus racemosus var. brevisetus M.E.Jones, Tium brevisetum (M.E.Jones) Rydb.
-
Description
Variety Description - Leaflets relatively narrow, the broadest on a plant 3-6 (8) mm. wide; flowers usually whitish, either concolorous or with lilac keel-tip, the wings and banner sometimes pinkish-purple or purple-veined; banner 16-19 mm. long.
Distribution and Ecology - Gullied bluffs, barren knolls, and alluvial bottomlands, on clay, shale or gypsum, 1700-4300 feet, locally abundant, southern Saskatchewan (local near Moose Jaw and on the headwaters of Qu’Appelle River) and North Dakota to western Oklahoma, the Texas Panhandle, and the Pecos Valley in eastern New Mexico, west just into eastern Wyoming and eastern Colorado, east to southeastern Nebraska and central Kansas; greatly isolated on dry lake beds at ± 6700 feet in western San Luis Potosi; reported from Minnesota (Fernald, 1950, p. 911, but no specimens at GH, MINN, or elsewhere).—Map No. 46.—May to July, flowering in late March southward.
-
Discussion
The alkali milk-vetch, A. racemosus, is a handsome floriferous species, impossible to confuse with any astragalus of the Prairie States other than the white-flowered forms of A. bisulcatus and distinguished from these by its sharply three-angled and three-sided pod. It is particularly common along dry water courses and on banks of running streams and rivers, and is likely to be met with wherever an accident of the terrain or of erosion has exposed a seleniferous formation; and it becomes abundant where destruction of the sod has given rise to a badlands topography. It is thence carried down to the alluvial flats and bottomlands, but in such situations is less frequent and less vigorous than A. bisulcatus. Its primary natural habitat on the open prairie was apparently around calcareous or shaley outcrops.
The flowers of var. racemosus are ordinarily pure white or creamy white with pinkish or lilac keel-tip. In Kansas and Oklahoma, possibly elsewhere, it is common to find a color- form in which a blush of anthocyanin extends from the base of the banner-blade upward around its margins and into the wing-tips, or is concentrated into a purple keel-tip and a fan of reddish-purple veins in the fold of the banner. Possibly this color-form is commoner than has been realized, for the pigment fades rapidly in drying and disappears completely after a few months. The type-collection of var. brevisetus, according to Jones’s field note (NY, POM), was such a form. Despite its remote origin at a point in Mexico over seven hundred miles south of the alkali milk-vetch’s southernmost outposts in Texas or New Mexico, var. brevisetus cannot be distinguished from typical material from the United States. In the original publication Jones referred to his new variety, which he did not separate from typical A. racemosus in specific terms, specimens from the Cimarron Valley, Oklahoma (Carleton 221, NY, US) and from "Fremont," properly Frontier County, Nebraska (Rydberg 70, NY); and I agree that these are exactly conspecific. Rydberg maintained a purely Mexican Tium brevisetum, supposedly differing in its short calyx-teeth (1.5-2 as opposed to 2.5-4 mm. long) and thick- textured foliage, the latter being a feature characteristic of A. racemosus sens. lat. Only two collections of A. racemosus have been seen from south of the border, and the species was possibly introduced in San Luis Potosí.
-
Objects
-
Distribution
Saskatchewan Canada North America| North Dakota United States of America North America| South Dakota United States of America North America| Wyoming United States of America North America| Nebraska United States of America North America| Kansas United States of America North America| Oklahoma United States of America North America| Texas United States of America North America| New Mexico United States of America North America| Colorado United States of America North America|