The Sandbar Milkvetch is known exclusively from the type material that had been collected in 1947 near Cameron in Coconino County, Arizona, USA, where the plant grew a gravelly washes and sandbars of summer-dry streams at elevations of 1110-1200 m.
This species was never found again and is believed to be extinct.
The Pseudocylindric Milkvetch was described in 1915, the species was apparently endemic to a very small area in the valley of the Euphrates in the Kemaliye District, Erzincan Province in eastern Turkey. 
The species appears to have been restricted to habitats close to the Euphrates river and disappeared when the Keban Dam was built from 1966 to 1974, probably due to habitat loss by rising of the river’s water level. 
References:  Zöhre Bulut; Hasan Yilmaz: The current situation of threatened endemic flora in Turkey: Kemaliye (Erzincan) case. Pakistan Journal of Botany 42(2): 711-719. 2010  Munir Ozturk; Umit Kebapci; Salih Gucel; Esat Cetin E.; Ernaz Altundag: Biodiversity and land degradation in the lower Euphrates subregion of Turkey. Journal of Environmental Biology 33: 311-323. 2012
Douglas’ Thistle Milkvetch (Astragalus kentrophyta var. douglasii)
The Thistle Milkvetch is a very thistle-like member of the legume family, the species includes around seven varieties which are distributed over a wide range of the southern USA.
The variety discussed here was described in 1964, it was restricted to a small area on the Colombia River at the boundery of Umatilla County in Oregon and Walla Walla County in Washington, USA.
Douglas’ Thistle Milkvetch hasn’t been collected since 1883, its habitat having been destroyed by dam projects and the plant is now considered extinct.
The photo below shows another variety, probably the nominate form.
References:  Astragalus kentrophyta Gray var. douglasii Barneby. Field Guide to Selected Rare Vascular Plants of Washington. Washington Natural Heritage Program and U.S.D.I. Bureau of Land Management 2005
Robbins’ Milkvetch (Astragalus robbinsii var. robbinsii)
Robbins’ Milkvetch was described in 1841, it includes around seven varieties which occur in northern North America, some have highly restricted ranges others are more common.
The nominate variety certainly was one of those with a rather restricted distributional area, it is known from limestone ledges on only a single site on the Winooski River in the town of Colchester in Chittenden County, Vermont, USA. This habitat was destroyed by the building of a dam in 1894, leading to the global extinction of this plant.
References:  Nathaniel Lord Britton; Addison Brown: An illustrated flora of the northern United States, Canada and the British possessions: from Newfoundland to the parallel of the southern boundary of Virginia, and from the Atlantic Ocean westward to the 102d meridian. New York: C. Scribner’s sons 1913