Monographs Details: Astragalus calycosus var. monophyllidius (Rydb.) Barneby
Authors:Rupert C. Barneby
Authority: Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(2): 597-1188.
Family:Fabaceae
Discussion:

337b. Astragalus calycosus var. monophyllidius

Habit of var. calycosus; leaflets solitary, terminal, 4—16 mm. long; apical sinus of the wings unappendaged; petals pink-purple.—Collections: 5 (iii); representative: Eastwood & Howell 9395 (CAS, WS); Ripley & Barneby 3550 (CAS, RSA), 6255 (RSA).

Open gravelly hillsides, in scattered juniper and piñon forest, on limestone, 5600-6500 feet, forming colonies but known only from a restricted area in northeastern Nye and Eureka Counties, eastcentral Nevada.—Map No. 154—May and June.

Astragalus calycosus var. monophyllidius (Rydb.) Barneby in Leafl. West. Bot. 3: 107. 1942, based on Hamosa monophyllidia (with one leaflet) Rydb. in N. Amer. Fl. 24: 421. 1929.—" ... in the vicinity of Currant, Nevada, May, 1916, Georgia H. Bentley.’’—Holotypus, NY! isotypi, DS, MO!

Differing from the nearly sympatric forms of the Torrey milk-vetch only in the loss of the last lateral pair of leaflets in all (or all but a very few) leaves, var. monophyllidius is but a minor, and most probably a very recent modification, scarcely deserving taxonomic recognition. The colonies of plants known to me along Currant Creek and on the slope falling eastward from Pinto Summit in Eureka County are essentially uniform, however, and seem to replace typical var. calycosus in their area of dispersal.