Astragalus missouriensis var. humistratus
Astragalus missouriensis var. amphibolus
archuleta milkvetch, Missouri milkvetch
Mancos milkvetch, Missouri milkvetch
10–15(–20) cm.
to 10 cm.
9–12-flowered.
4–8-flowered.
calyx 7.8–10 mm, tube 6–10 mm, lobes 1.5–3 mm;
corolla lavender, purple, or almost white, wing tips often white;
banner (17–)19–20.5 mm.
calyx 8.5–13 mm, tube 7–10 mm, lobes 1.5–3 mm;
corolla usually pink-purple, rarely white;
banner (14.5–)16–22(–24) mm;
keel (11.5–)12.8–17.3(–18.5) mm.
ascending to descending, dorsiventrally compressed, lunately incurved, oblong-ellipsoid, (12–)17–20 × 6–9 mm, unilocular, apex obcompressed proximal to incurved beak, glabrous or sparsely strigulose.
sometimes deciduous, ascending to descending, dorsiventrally compressed, lunately incurved, ellipsoid, (11–)15–25 × 7–9 mm, unilocular, apex obcompressed proximal to incurved beak, strigose.
33–40.
35–55.
Astragalus missouriensis var. humistratus
Astragalus missouriensis var. amphibolus
Variety humistratus is locally distributed in Archuleta, Hinsdale, and La Plata counties, Colorado, and adjacent Rio Arriba County, New Mexico. It is anomalous in its strongly caulescent but mat-forming habit, and the slightly or plainly connate stipules. R. C. Barneby (1964) suggested a hybrid origin between Astragalus missouriensis and A. humistratus.
Variety humistratus is in the Center for Plant Conservation’s National Collection of Endangered Plants.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
The fruits of var. amphibolus are initially dorsiventrally compressed, and ultimately dehisce apically while still attached to the inflorescence (though sometimes deciduous). The fruits have a lateral ridge down each valve, with the valves separated by more or less prominent bicarinate keels. In these features, along with the typically persistent fruits, the plants can be distinguished from the similar Astragalus amphioxys var. amphioxys where their ranges are contiguous, as in northwestern New Mexico and vicinity. R. C. Barneby (1947b, 1964) suggested that hybridization occurs between the two taxa.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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