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Astragalus cremnophylax var. cremnophylax
Astragalus cremnophylax Barneby var. cremnophylax
Grand Canyon Cliff Milkvetch, Grand Canyon Sentry Milkvetch, Sentry Milkvetch
Fabaceae (Pea family)
Synonym(s):
USDA Symbol: ASCRC4
USDA Native Status: L48 (N)
"A member of the pea family (Fabaceae), this dwarf, evergreen, perennial, mat-forming herb with a thick taproot, is usually less than 2.5 cm (1.0 in.) high and 2.5 to 25.0 cm (1.0 to 10 in.) in diameter." (webref: 58).
"The sentry milk-vetch is one of our rarest species. It was first discovered in 1903 by Marcus Jones, who mistook it for A. humillimus and reported it (1923, p. 82, Pl. 6, fig. 19) as "apparently common at the Grand Canyon ... on sandy ledges." Search in recent years has revealed, however, only a single group of perhaps a hundred plants confined to a strip of rock pavement not over fifty yards in length. They are scattered over the area, some in full sun and rooting in scarcely visible cracks of the limestone, others standing back among the piñons and rooting into sand-filled hollows of the rock. It is to be sought elsewhere in the region, perhaps on some of the buttes which stand out in isolation from the canyon wall." (bibref: 1814).
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Plant Characteristics
Duration: PerennialHabit: Herb
Leaf Arrangement: Alternate
Fruit Type: Legume
Size Notes: "Dwarf, evergreen, perennial, mat-forming herb with a thick taproot, is usually less than 2.5 cm (1.0 in.) high and 2.5 to 25.0 cm (1.0 to 10 in.) in diameter." (webref: 58).
Leaf: "Short creeping stems have compound leaves 1.3 cm (0.5 in.) long, composed of 5-9 tiny leaflets 1-2 mm long." (webref: 58).
Flower: "A large number of tiny, pea flowers are produced; 100-200 per plant is not uncommon. Flowers are whitish or pale pinkish-lilac in color, 5 mm long, and borne on a raceme of 1-3 flowers, held slightly above the mat." (webref: 58).
Fruit: "The fruit is unilocular, obliquely egg-shaped, and densely hairy, 3-4 mm long. Fruits vary in number from 1->700 per plant depending on size, amount of damage, and health of plant. Each fruit produces 1-6 orange seeds; the average number is 3. Seeds are 1 mm in length. Fruits from late May-June." (webref: 58).
Bloom Information
Bloom Color: White , Pink , Purple , VioletBloom Time: Mar , Apr , May , Sep , Oct , Nov
Bloom Notes: "Flowers are whitish or pale pinkish-lilac in color." (webref: 58). "March-April (late April to early May) and September-November, spring more common." (webref: 58).
Distribution
USA: AZNative Distribution: "There are four known populations on the edges of the South Rim of the Grand Canyon (USFWS 2018). Some of these populations have additional sub-populations and some groups of new plants have been discovered on limestone fingers along and below the rim. Known populations occur only in Coconino County. Three populations have recently been discovered on the North Rim, and preliminary genetic results suggest they would be ascribed to sentry milk-vetch." (webref: 58).
Native Habitat: "Plants grow in the uppermost layer of a very peculiar white layer of limestone that is not grossly fractured, but rather weathers in small, shallow pockets and networks of small cracks. This kind of limestone (Kaibab limestone) is exposed for only a few hundred square yards, forms large flat platforms, has shallow soils (< 7 cm deep), is unshaded, and in the pinon-juniper-cliffrose plant community above 1219 m (4,000 ft). In these openings, sentry milk-vetch is co-dominant with rock mat (Petrophytum caespitosum). 7,000 - 7,360 ft. (2135 - 2243 m) for South Rim populations. About 7900 feet (2410 m) for the North Rim populations." (webref: 58).
U.S. Fish & Wildlife Service Threatened & Endangered Status
USFWS Species Profile: Q1T8Status:Bibliography
Bibref 1814 - Atlas of North American Astragalus Volume 2 (1964) Barneby, Rupert C.Search More Titles in Bibliography
Web Reference
Webref 58 - Arizona’s Natural Heritage Program: Heritage Data Management System - HDMS (2020) Arizona Game & Fish DepartmentAdditional resources
USDA: Find Astragalus cremnophylax var. cremnophylax in USDA PlantsFNA: Find Astragalus cremnophylax var. cremnophylax in the Flora of North America (if available)
Google: Search Google for Astragalus cremnophylax var. cremnophylax
Metadata
Record Modified: 2020-12-07Research By: Joseph A. Marcus