Astragalus oocalycis

  • Title

    Astragalus oocalycis

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Astragalus oocalycis M.E.Jones

  • Description

    110. Astragalus oocalycis

    Commonly stout, with a woody, multicipital taproot, thinly strigulose with fine, straight, appressed hairs up to 0.5-0.75 mm. long, the herbage full-green or pallidly gray-green, the leaflets glabrous or nearly so above (but their elevated margins beset with a row of stiff hairs directed inward toward the midrib), the inflorescence silky-hirsute; stems erect and ascending in bushy clumps, (1.5) 2.5-4 dm. long, simple except for a rare spur from below the middle, composed of some 6-13 developed internodes, leafless at base, abruptly flexuous or zigzag distally; stipules scarious or early becoming so, 2.5-6 mm. long, the lowest amplexicaul and united into a bidentate sheath (this commonly ruptured by the expanding stem), the median and upper ones free or united by a narrow membrane or stipular line, with deltoid-acuminate, mostly reflexed blades; leaves 5-15 (17) cm. long, the lower ones shortly petioled, the rest subsessile, with (9) 19-27 linear or linear- oblong, acute, or obtuse and mucronulate, flat or commonly loosely inrolled, thick- textured leaflets (1) 2-4 cm. long; peduncles stout, erect, 9-17 cm. long; racemes spiciform, densely 35-60-flowered, broadly cylindric at full anthesis, the subsessile flowers spreading and soon declined, the axis scarcely elongating, 4-8 (11) cm. long in fruit; bracts membranous, narrowly lanceolate, 3-8 mm. long, becoming papery and abruptly deflexed in fruit; calyx hirsute with straight, ascending and spreading hairs up to 1-1.5 mm. long, at early anthesis obliquely ovoid and 10-11 mm. long, the shallow disc 0.7-0.9 mm. deep, the tube early accrescent, at length papery and inflated, broadly ovoid to subglobose, up to 14 mm. long and 11 mm. in diameter, contracted at the mouth, the erect or connivent, triangular-subulate teeth 2-3 mm. long, the whole disjointing in age and falling with the ripe fruit; petals ochroleucous, marcescent; banner sigmoidally arched, the claw following the ventral curvature of the calyx, the whole broadly oblanceolate or obovate-cuneate, 14-17 mm. long, 6.4-7.6 mm. wide; wings 13-14.5 mm. long, the claws 6.3-7.6 mm., the oblong-oblanceolate or -elliptic, obtuse or emarginate, nearly straight blades ± 8 mm. long, 2.6-3.7 mm. wide; keel 11.2-13 mm. long, the claws 5.8 7.6 mm., the lunately half-elliptic blades db 6 mm. long, 2.7-3.4 mm. wide, gently incurved through 45° to the rounded apex; anthers 0.7-0.85 mm. long; pod sessile on and ultimately disjointing from a slender, stipelike gynophore ± 1 mm. long, included within the calyx, the gynophore ascending and then abruptly bent at apex through nearly 90° (the pod-body therefore declined), the body oblong-ellipsoid, 6-7 mm. long, ±3.5 mm. in diameter, rounded or subtruncate at base, abruptly cuspidate-beaked, straight or a trifle incurved, strongly obcompressed, with convex dorsal and openly grooved ventral faces, the sutures both prominent, the ventral one forming an elevated keel lengthwise within the shallow ventral sulcus, the thinly fleshy, glabrous valves becoming leathery, transversely rugulose-reticulate, not inflexed; seeds brown, smooth but dull, 2.8-3.4 mm. long.—Collections: 5 (i); representative: Weber & Livingston 6233 (CAS, OKLA, SMU, TEX); M. & G. Ownbey 3033 (NY, RSA, SMU, TEX, WS); Ripley & Barneby 5334 (CAS, NY, RSA).

    Dry knolls, gullied clay hillsides, gulches in sagebrush plains, and alluvial bottomlands, in stiff alkaline gumbo-clay soils, 5600-6700 feet, forming colonies but quite local, known only from a small area on and near the upper forks of the San Juan River in western Archuleta and adjoining La Plata Counties, Colorado, and northeastern San Juan County, Arizona.—Map No. 47.—May to July.

    Astragalus oocalycis (with egg-shaped calyx) Jones, Contrib. West. Bot. 8: 10. 1898.— "... on bottom lands at Aztec, New Mex. and communicated by Prof. Wooton."—Holotypus collected in July, 1895, POM!—Diholcos oocalycis (Jones) Rydb. in N. Amer. Fl. 24: 282. 1929.

    Cnemidophacos urceolatus (shaped like a small pitcher, of the calyx) Rydb., Fl. Rocky Mts. 502. 1917.—"Mountains: Colo."—Holotypus, C. F. Baker 424, collected at Arboles, Colorado, June 3, 1899, NY! isotypi, G, GH, K, MO, ND, US!

    By any standard of comparison, whether subjective and aesthetic or severely technical, the Arboles milk-vetch, A. oocalycis, is a remarkable astragalus. A vigorous, handsome plant, it combines the foliage of some Pectinati (but the long, stiff, pseudopetiolulate leaflets uncommonly numerous) with the small, ventrally bisulcate pod of A. bisulcatus var. Haydenianus. The pod differs, however, in being sessile on a gynophore and not truly stipitate as in the genuine Bisulcati. The most striking feature of the species is its subsessile, at length ovoid, and greatly inflated calyx, densely hirsute with cream-colored hairs, which is in contrast to the nearly glabrous foliage. Moreover the many crowded flowers are sessile or almost so, the inflorescence therefore becoming a massive, cylindro-oblong, spiciform head.

    A calyx greatly inflated and finally accrescent so as to enclose a small, few-seeded pod has no match among American astragali, although there is some approach to this condition in sect. Chaetodontes. It is a rather common development in Asia, Bunge’s two subgenera Calycocystis and Calycophysa being so characterized. The latter group has basifixed pubescence as in Oocalyces, but the claws of the inner petals are normally fused for a short distance with the staminal sheath. Undoubtedly, this modification of the calyx has occurred independently in the Arboles milk-vetch, of which the affinities, loosely speaking, have been apparent from the first. Jones aligned A. oocalycis with his Bisulcati (1923, p. 245), remarking that it "had the appearance of a sport, and the general look of A. racemosus," the species placed immediately after it in sect. Galegiformes. Rydberg first interpreted it as a Cnemidophacos, a genus which embraced our Ocreati and Pectinati, but following Jones he finally transferred it to Diholcos (= our Bisulcati), where it was maintained by Porter (1939). There has been a general agreement on the phyletic position of A. oocalycis among the seleniferous groups with connate stipules, an agreement which took form before its physiological adaptation to selenium was suspected; but if we assume that the species is derived from a common ancestry with the Pectinati, Bisulcati, Albuli, and Ocreati, we have no clue to its immediate precursor. It is tempting to suppose that the similarity in form of the pod-body between A. oocalycis and A. bisulcatus var. Haydenianus and the fact that these two poisonous vetches are found on the same shaley outcrops on the upper San Juan are causally related. But if A. oocalycis arose through hybridization involving var. Haydenianus, we have yet to find a sympatric second parent; and if by mutation directly from var. Haydenianus, we must admit that a mutation which involved so great a modification of the flower, and a simultaneous advance from an emmenoloboid to a piptoloboid fruit, gave rise in effect to an astragalus of a new and unprecedented type. So far as the fruit alone is concerned, A. oocalycis has more in common with A. (Ocreati) flavus than with the Bisulcati, but the foliage and flowers are very different. No species better deserves a monotypic section.

    According to Jones (1923, Pl. 63) the pod of the Arboles milk-vetch varies from "almost sessile to long-stipitate," and the cited figure shows one apparently immature fruit already well exserted from the calyx and a cross-section distinguished by a pronounced lateral compression. No pod of this nature is now found on the type sheet, and it seems hardly possible that the fruit illustrated can have belonged to A. oocalycis.