Dougl. ex Hook.
Astragalus lentiginosus is a species of legume known by the common name freckled milkvetch. It is native to western North America from British Columbia to Texas and northern Mexico, where it grows in many habitat types. There are a great number of wild varieties of this species, and they vary in appearance. The flower and the fruit of a given individual are generally needed to identify it down to the variety. This is usually a perennial herb with leaves up to 15 centimeters long divided into many pairs of small leaflets. The inflorescence holds up to 50 pealike flowers which may be purplish or whitish or a mix of both. The fruit is an inflated, beaked pod with a groove along the side. It dries to a papery texture and releases the seeds when it is broken.
Astragalus lentiginosus is a diverse set of forms varying from prostrate to erect, glabrous to tomentose, annual to perennial and with flowers from purple to white. A unifying character among most of the varieties is an inflated, bilocular pod with a unilocular beak. This unilocular beak dehisces at maturity to allow seeds to be dispersed from the fruit. Some varieties have slightly inflated pods where the abaxial suture does not extend all the way to the funicular flange, resulting in a semi-bilocular condition. The epithet lentiginosus refers to the red mottling commonly found on the pods (but not exclusively) which resemble freckles.
Many of what we currently know as varieties of Astragalus lentiginosus were originally described as species. Marcus E. Jones was the first to recognize the similarities among these taxa and arranged them as varieties of one species (Jones 1895, 1923). Per Axel Rydberg employed a very different species concept stating that he did not believe in infra-taxa (Rydberg 1929b). This resulted in his raising Jones’s varieties to species in the genera Cystium and Tium (Rydberg 1929a). A notable novelty of Rydberg’s treatment is the concept of sections which have been maintained in the keys of subsequent treatments, even if this was not explicitly stated.
Subsequent treatments include Barneby (1945, 1964, 1989), Isely (1998), and Welsh (2007). Each of these treatments are slightly different, containing between 36 and 42 taxa. Recent molecular work seems to suggest a genetic component to the varieties (Knaus et al. 2005). Currently the following 40 taxa are recognized:
A. l. var. albifolius M.E.Jones 1923.
A. l. var. ambiguus Barneby 1964.
A. l. var. antonius Barneby 1945.
A. l. var. araneosus (E.Sheld.) Barneby 1945.
A. l. var. australis Barneby 1945.
A. l. var. borreganus M.E.Jones 1898.
A. l. var. chartaceus M.E.Jones 1895.
A. l. var. coachellae Barneby 1964.
A. l. var. diphysus (A.Gray) M.E.Jones 1895.
A. l. var. floribundus Gray 1865.
A. l. var. fremontii (A.Gray 1857) S.Watson 1871.
A. l. var. higginsii S.L.Welsh 1981.
A. l. var. idriensis M.E.Jones 1902.
A. l. var. ineptus (A.Gray) M.E.Jones 1923.
A. l. var. kennedyi (Rydb.) Barneby 1945.
A. l. var. kernensis (Jeps.) Barneby 1945.
A. l. var. latus (M.E.Jones) M.E.Jones 1923.
A. l. var. lentiginosus Barneby 1964.
A. l. var. maricopae Barneby 1945.
A. l. var. micans Barneby 1956.
A. l. var. mokiacensis (A.Gray) M.E.Jones 1923.
A. l. var. multiracemosus S.L.Welsh & N.D.Atwood 2007.
A. l. var. negundo S.L.Welsh & N.D.Atwood 2007.
A. l. var nigricalycis M.E.Jones 1895.
A. l. var. oropedii Barneby 1945.
A. l. var. palans (M.E.Jones) M.E.Jones 1898.
A. l. var. piscinensis Barneby 1977.
A. l. var. pohlii S.L.Welsh & Barneby 1981.
A. l. var. salinus (Howell) Barneby 1945.
A. l. var. scorpionis M.E.Jones 1923.
A. l. var. semotus Jeps. 1936.
A. l. var. sesquimetralis (Rydb.) Barneby 1945.
A. l. var. sierrae M.E.Jones 1923.
A. l. var. stramineus (Rydb.) Barneby 1945.
A. l. var. trumbullensis S.L.Welsh & N.D.Atwood 1981.
A. l. var. ursinus (A.Gray) Barneby 1945.
A. l. var. variabilis Barneby 1945.
A. l. var. vitreus Barneby 1945.
A. l. var. wilsonii (Greene) Barneby 1945.
A. l. var. yuccanus M.E.Jones 1898.
As a species, Astragalus lentiginosus is distributed throughout the North American continent, west of the Rocky Mountains, east to the Californian Coast Range, south to Northern Mexico, and north to Southern British Columbia. The varieties are largely limited to marginal habitats such as disturbed sites in the arid regions of the continent. The group also contains a number of edaphic specialists which occur at desert seeps which frequently exhibit high levels of calcium carbonate.
Astragalus lentiginosus is currently not cultivated commercially. Propagation from seed requires scarification of the seed coat in order for the embryo to imbibe water.
Barneby, R.C. 1945. ‘’Pugillus Astragalorum’’ IV: the section ‘’Diplocystium’’. Leaflets of Western Botany 4: 65-152.
Barneby, R.C. 1964. Atlas of North American ‘’Astragalus’’. Memoirs of the New York Botanical Garden 13: 1-1188.
Barneby, R.C. 1989. Intermountain Flora: Fabales vol. 3B: 157-162.
Isely, D. 1998. Native and Naturalized Leguminosae (Fabaceae) of the United States: 318-337.
Jones, M.E. 1895. Contributions to Western Botany. Proceedings of the California Academy of Sciences 5: 672-675.
Jones, M.E. 1923. Revision of North-American Species of ‘’Astragalus’’.
Knaus, B.J., Cronn, R., and Liston, A. Genetic characterization of three varieties of Astragalus lentiginosus (Fabaceae). Brittonia 57(4): 334-344.
Rydberg, P.A. 1929a. Astragalanae. North American Flora 24(5): 252-322???
Rydberg, P.A. 1929b. Scylla or Charbdis. International Congress of Plant Sciences: 1539-1551.
Welsh, S.L. 2007. North American Species of ‘’Astragalus’’ Linnaeus (Leguminosae) a taxonomic revision. Monte L. Bean Life Science Museum.