Astragalus chamaeleuce A.Gray

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

Scientific Name

Astragalus chamaeleuce A.Gray

Type

“Rocky Mountains, on the hills of Ham’s Fork of the Colorado of the West...Nuttall."—Holotypus, labeled by Nuttall "Phaca *pygmaea. R. Mts.," BM! isotypus, NY!

Synonyms

Phaca pygmaea Nutt., Tragacantha pygmaea (Nutt.) Kuntze, Xylophacos pygmaeus (Nutt. ex Torr. & A.Gray) Rydb., Astragalus pygmaeus (Nutt. ex Torr. & A.Gray) M.E.Jones, Astragalus cicadae M.E.Jones, Astragalus pygmaeus var. cicadae (M.E.Jones) M.E.Jones, Astragalus cicadae var. laccoliticus M.E.Jones, Astragalus pygmaeus var. laccoliticus (M.E.Jones) M.E.Jones

Description

Species Description - Low, tufted, acaulescent or very shortly caulescent, sometimes flowering the first season but ultimately forming a shortly forked caudex, densely strigulose throughout or nearly so with rather coarse, straight or nearly straight, appressed or some narrowly ascending hairs up to 0.7-1.15 mm. long, the herbage cinereous or canescent, the vesture of the upper surface of the leaflets often assuming a golden-green hue when dried; stems few or several, either reduced to sessile crowns or slightly developed and up to 3 (6) cm. long, then prostrate, the internodes not over twice as long as the stipules, mostly shorter; stipules submembranous becoming papery, ovate-triangular or triangular-acuminate, 2—7 mm. long, semiamplexicaul-decurrent; leaves 2—8 (11) cm. long, with rather firm but almost always deciduous petiole and (1) 5—15 (17) broadly obovate, obovate-cuneate, or rarely oblanceolate, mostly obtuse or truncate-emarginate, exceptionally rhombic-oval and subacute, flat, rather thick-textured leaflets (2) 4-13 (15) mm. long, those of the lower leaves (especially of seedling plants) often fewer and larger than those of later ones, sometimes solitary; peduncles rather stout, (1) 2-6 cm. long, shorter than the leaves, incurved-ascending at anthesis, arcuate-procumbent in fruit; racemes shortly or subumbellately (2) 4-11-flowered, the flowers spreading or ascending, the axis little elongating, (0.3) 1-2 cm. long in fruit; bracts papery- membranous or early becoming so, ovate-triangular to broadly lanceolate, 2-5 mm. long; pedicels at anthesis ascending, straight, 1-2 mm. long, in fruit either ascending or arched outward, 1.8-3.5 mm. long; bracteoles usually 0, rarely 1-2, minute; calyx 9.1-12.4 (13.5) mm. long, strigulose with black, black and white, or all white hairs, the slightly oblique disc 0.9-2 mm. deep, the submembranous, purplish, cylindric or exceptionally deep campanulate tube 6.7-9.5 (12) mm. long, 3.2—4.5 mm. in diameter, the subulate teeth 1.4-2.9 mm. long; petals either ochroleucous with dull purple keel-tip, or ochroleucous tinged with lurid purple, or bright pink-purple except for pale claws and pale lozenge in the fold of the banner; banner recurved through ± 45°, broadly oblanceolate, rhombic- oblanceolate, or obovate-spatulate, shallowly notched, 17-24 (25.5) mm. long, 8.2-12 mm. wide; wings a little shorter or rarely as long, 16.6-22.4 mm. long, the claws 8.1-12 mm., the narrowly lance-oblong, obtuse or obliquely emarginate blades 9.3-12 mm. long, 2.2-3 mm. wide, commonly a little incurved in the distal ½; keel 14.6-20 (22) mm. long, the claws 8.1-12.7 (13.3) mm., the lunately half-oval or -obovate blades 6.5—8 (9) mm. long, 2.9—3.7 mm. wide, incurved through 85—95° to the rounded apex; anthers 0.5—0.7 (0.75) mm. long; pod ascending (humistrate), obliquely oblong-ovoid or -ellipsoid, (2) 2.5-4 cm. long, (7) 9-16 mm. in diameter, rounded at base, a little dorsiventrally compressed and shallowly sulcate ventrally in the lower ½-?, thence passing upward, gradually or abruptly, into a short, obconic or deltoid, laterally compressed, shortly cuspidate beak, slightly but definitely incurved, the fleshy valves ± 3 mm. thick when fully formed, shrinking somewhat in ripening, composed of a leathery endocarp and a fragile, papery exocarp separated by a layer of dry, spongy-alveolate tissue, the outermost skin at first greenish and commonly purple-mottled and -speckled, densely strigulose or rarely glabrous, transversely reticulate, ultimately becoming stramineous, lustrous, separating from the veins beneath, then appearing quite smooth; dehiscence apical, after falling; ovules 38-60; seeds pale pinkish- or ocher-brown, pitted and rugulose, 2.4—3 mm. long.

Distribution and Ecology - Dry open bluffs, gullied hillsides, knolls, and canyon benches, in gravelly or sandy, often alkaline clay soils derived mostly from shale or sandstone, sometimes in coarse alluvia of cobblestone bluffs, rarely in broken lava, 4750—7000 (8350) feet, rather common and locally plentiful in the Colorado and Green River Basins, from the foot of the Henry Mountains in eastern Garfield County, Utah, north through northwestern Colorado and the Uinta Basin to southwestern Wyoming, extending less commonly across the Continental Divide to the upper Wind and Big Horn Rivers in westcentral Wyoming.—Map No. 91.—Late April to June, into July northward.

Discussion

The cicada milk-vetch, in the Uinta Basin called "Popper" from the crackle of the ripe pods underfoot, is the only astragalus of its type known to occur in Utah north of Tavaputs Escarpment or in western Wyoming. On the lower Grand River in Colorado it is sympatric and sometimes closely associated with A. amphioxys var. vespertinus; south of the Escarpment in Utah (where it seems to be extremely rare) its range overlaps those of A. amphioxys var. amphioxys and A. cymboides. Flowering plants of these species are identified with difficulty. Fortunately the extremely distinct fruits ripen early, for they are often necessary in determining the correct name. The ripe pod of A. Chamaeleuce is remarkable for the textural differentiation of the three layers of cellular tissue of which the valve walls are composed. The thick mesocarp is made up of unusually large cells at first laden with a sweetish sap, which is gradually withdrawn as the seeds ripen, leaving a fragile honeycomb of pith. Consequently, the ripe fruit is so light in relation to its mass that it may be dispersed readily by the wind. The thin, reticulately veined outer skin, which ripens to a papery-membranous texture, suggests the glassy transparency of a locust’s wing.

The named varieties of the cicada milk-vetch were based on individual variations and have no claim to taxonomic rank. At the time Jones described A. cicadae he was ignorant of the true nature of A. Chamaeleuce, for he compared his new species only with A. amphioxys and the distantly related A. megacarpus. Subsequently (1923, p. 211) he applied the trinomial A. pygmaeus var. cicadae to the material of A. chamaeleuce from the Uinta Basin southward, but he advanced no effective differential characters distinguishing it from the typical form. Nearly all examples of the cicada milk-vetch from north of the Uinta Mountains have 50-60 ovules as opposed to 37-46 southward, which suggests incipient racial differentiation; but no other consistent difference is apparent. The var. laccoliticus was described by Jones (1923, p. 211) as suggesting a hybrid between A. chamaeleuce and A. musiniensis, on account of its subacute leaflets and rather strongly incurved pod. However neither of the supposed parents was found by Jones in the Henry Mountains, and a hybrid hypothesis seems superfluous to account for the hardly unusual appearance of the type-collection. As the Henry Mountains are remote from the main range of A. chamaeleuce, the habitat on "volcanic gravel" is strange for the species. Fresh young material from this region collected earlier in the year is required.

Objects

Specimen - 801249, A. Nelson 4605, Astragalus chamaeleuce A.Gray var. chamaeleuce, Fabaceae (152.0), Magnoliophyta; North America, United States of America, Wyoming

Distribution

Utah United States of America North America| Colorado United States of America North America| Wyoming United States of America North America|