Flora of North America species comparison

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Astragalus amphioxys var. modestus

Astragalus amphioxys var. musimonum
Photo is of parent taxon

crescent milkvetch, modest milkvetch
Photo is of parent taxon

crescent milkvetch, sheep mountain milkvetch
Flowers

calyx cylindro-campanulate, tube 6.1–9.3 mm, lobes 1.1–2.6 mm;

corolla banner 12.8–16 mm;

keel 11–12.7 mm.

calyx campanulate, tube 3.4–4.8 mm, lobes 1.8–2.5 mm;

corolla banner 10.3–13.4 mm;

keel 8–11.5 mm.
Legumes

16–40 mm, crescentic or incurved through 1/2 their length.

15–20(–25) mm, crescentic or incurved through 1/2 their length.
Seeds

44–58.

26–36.

Astragalus amphioxys var. modestus

Astragalus amphioxys var. musimonum
Phenology Flowering Mar–May. Flowering Apr–Jun.
Habitat Dry gravelly hillsides, in blackbrush, four-wing saltbush, Indian ricegrass, needle-and-thread grass, old man sagebrush, mixed grass communities, on sandy silt, limestone, or cindery volcanic debris. Limestone gravel and outcrops with blackbrush.
Elevation 1100–1500 m. (3600–4900 ft.) 1100–1800 m. (3600–5900 ft.)
Distribution
from FNA
AZ; NV; UT; Dry gravelly hillsides; in blackbrush; four-wing saltbush; Indian ricegrass; needle-and-thread grass; old man sagebrush; mixed grass communities; on sandy silt; limestone; or cindery volcanic debris
[BONAP county map]
from FNA
AZ; NV
[BONAP county map]
Discussion

The small-flowered var. modestus forms the other major extreme in flower size within the species, contrasting with the large-flowered var. vespertinus. It is local, forming uniform colonies within the range of var. amphioxys but only from valleys affluent to the Colorado River from San Juan and eastern Kane counties, Utah, and northern Mohave County, Arizona, with disjunct populations in Lincoln County, Nevada. Some plants from northeastern Arizona and northwestern New Mexico have similarly small flowers and might represent an eastward extension of var. modestus; however, in this case introgression from Astragalus missouriensis cannot be ruled out.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Variety musimonum is found on the Shivwits Plateau in Mohave County, Arizona, westward to the Sheep Mountain Range in Clark County, Nevada.

The combination of a sharply curved tip of the fruit, short petal claws, and small calyx has been considered sufficient to recognize this taxon as a distinct species, Astragalus musimonum (D. Isely 1998).

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 11. FNA vol. 11.
Parent taxa Fabaceae > subfam. Faboideae > Astragalus > sect. Argophylli > Astragalus amphioxys Fabaceae > subfam. Faboideae > Astragalus > sect. Argophylli > Astragalus amphioxys
Sibling taxa
A. amphioxys var. amphioxys, A. amphioxys var. musimonum, A. amphioxys var. vespertinus
A. amphioxys var. amphioxys, A. amphioxys var. modestus, A. amphioxys var. vespertinus
Synonyms A. musimonum
Name authority Barneby: Leafl. W. Bot. 9: 89. (1960) (Barneby) Barneby in A. Cronquist et al.: Intermount. Fl. 3(B): 138. (1989)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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