OregonFlora species comparison

Cosmopolitan in Northern Hemisphere, secondarily extending into Southern Hemisphere. ~1500–2000 species; 56 species treated in Flora.

Many species of Oxytropis can be mistaken for species of Astragalus; see the discussion under Oxytropis for differences between the genera. Mature fruits are often required for the keys to work. Cross sections of the fruit body show if it is internally unilocular or bilocular through the intrusion of the dorsal suture. In some cases, the dorsal suture may not completely divide the locule. If the locule is almost but not quite divided, the pod can be said to be semibilocular; if the intrusion into the locule is present but there is an obvious space between the sutures, the pod can be said to be subunilocular. Gradations do exist between these forms. The stipe is derived from the ovary and is part of the pod; this stalk can elevate the pod some distance beyond the mouth of the calyx. The gynophore is of receptacular origin and not part of the fruit; it is a stalk that also elevates the pod. Careful observation of the stipule is also important in species determination in Astragalus. Stipules may be free and monomorphic. Stipules may also be dimorphic, with the stipules at lowermost 1–3(4) nodes connate and sheathing, while the upper stipules are typically free. Astragalus species are among the most important toxic plants in North America. Livestock losses due to ingestion of these plants are of major economic concern to ranchers. Locoism is caused by the presence of indolizidine alkaloids; cracker-heels disease is caused by the presence of toxic glycosides or nitrotoxins; selenosis is caused by the presence of high levels of selenium in the soil and its subsequent accumulation in the tissues of the plants growing in these soils. The toxicity of all species of Astragalus is unknown. In Oregon, species that cause problems include Astragalus canadensis, A. curvicarpus, A. lentiginosus, A. reventus, and A. succumbens. Considering the large number of species of Astragalus worldwide and their ecological amplitude, it is surprising that there are essentially no exotic species found in Oregon. Astragalus drummondii, Drummond’s milkvetch, has been collected in Oregon twice: once in Douglas County in 1887 and once in Wasco County in 1927. It has not persisted and is considered a waif. It is native from the east base of the Rocky Mountains from Montana to Utah, east to Colorado and the Dakotas. Drummond’s milkvetch can be recognized by villous pubescence, large nodding yellow or white flowers and pendulous, stipitate, glabrous pods. Astragalus cicer, chickpea milkvetch, a native of Europe, has been introduced into North America as an experimental forage crop, ornamental novelty, and in reclamation plantings. It has escaped and become naturalized in California, Idaho, Nevada, Washington, and else­where, so it could appear in Oregon. It can be recognized by its sprawling growth form, yellowish flowers, and swollen, black-hairy, sessile, bilocular pods.