Astragalus Cronquistii

  • Title

    Astragalus Cronquistii

  • Author(s)

    Rupert C. Barneby

  • Scientific Name

    Astragalus cronquistii Barneby

  • Description

    54. Astragalus Cronquistii

    Diffuse, perennial, with a stout taproot and buried root-crown, strigulose with subappressed (and a few narrowly ascending), filiform or flattened and scalelike hairs up to 0.2—0.5 mm. long, the stems cinereous distally, the herbage bicolored, the leaflets gray and densely pubescent beneath, yellowish-green and glabrous to thinly and minutely pubescent above; stems several, decumbent and radiating, (1.5) 2-4 dm. long, subterranean for a space of 5-14 cm., simple or divaricately branched or spurred at 1—3 nodes preceding the first peduncle, floriferous upward from near or above the middle; stipules 2—6 mm. long, dimorphic, those at the buried nodes papery, pallid or brownish, adnate to the vestigial petiole to form a bidentate sheath embracing ±3/4 the stem’s circumference, the upper ones herbaceous, deltoid to triangular, often spreading or deflexed; leaves 1.5-4.5 cm. long, mostly divaricate or recurved, sessile or nearly so, with 7—15 oblong-elliptic to linear-oblong, deeply retuse to truncate-emarginate, flat or loosely folded leaflets 6-20 (23) mm. long; peduncles divaricate and incurved-ascending, 2-6.5 cm. long; racemes loosely 6-20-flowered, the flowers nodding at full anthesis, the axis (1.5) 2-6.5 (8.5) cm. long in fruit; bracts triangular-subulate, 0.6-1.2 mm. long; pedicels at anthesis arched outward, in fruit ascending at a wide angle, divaricate, or recurved, thickened, 2-2.5 mm. long, tardily disjointing with the fruit; bracteoles 0; calyx ± 4 mm. long, strigulose with white and sometimes a few fuscous hairs, the campanulate tube ± 3-4 mm. long, 2.2-2.5 mm. in diameter, the broadly subulate or triangular teeth 0.5-1 mm. long, separated by wide, obtuse sinuses, the whole becoming papery, ruptured, persistent; petals pink-purple, the wing- and keel-tips paler; banner recurved through 90-100°, broadly obovate- cuneate, openly notched, ± 8 mm. long, 5.5 mm. wide; wings nearly as long, the claws ± 4 mm., the obovate, obtuse or subemarginate, incurved blades ± 5 mm. long; keel nearly as long as the banner, the claws 4-4.5 mm., the almost halfcircular blades ± 4 mm. long, 2.6-3 mm. in diameter, incurved through 100120° to the sharply deltoid apex; pod declined or pendulous, sessile or contracted at base into an incipient stipe up to 0.8 mm. long, the body linear-elliptic, linear, or obscurely linear-oblanceolate in profile, straight to gently incurved (rarely a trifle decurved), (2) 2.2-3 cm. long, 3.5-4.8 mm. in diameter, bluntly trigonous, keeled ventrally by the prominent suture, openly grooved dorsally, the lateral faces low- convex, the lateral angles rounded, the thin, green or faintly red-dotted, strigulose valves becoming stramineous, papery, cross-reticulate, inflexed as a rudimentary septum 0.3-0.6 mm. wide; dehiscence unknown; seeds oblong or prismatic, greenish-brown and purple-dotted, pitted but sublustrous, 3.6-4.8 mm. long.—Collections: 2 (o); representative: Welsh 1505 (NY).

    Low sandy and gravelly ridges, on red sandstone, ± 4000 feet, known only from the type-locality and vicinity in Comb Wash west of Bluff, San Juan County, Utah.—Map No. 24.—Late April to May.

    Astragalus Cronquisth (Arthur John Cronquist, 1919- ), sp. nov., nulli arete affinis, inter Lonchocarpos ob stipulas imas (subterraneas) petiolo vestigiali adnatas inter se liberas et legumen pendulum persistens collocanda, foliis imparipinnatis A. titanophilum necnon subsect. Aequales simulans sed ab illis legumine trigono dorso sulcato cito diagnoscenda. Species ab omnibus Lonchocarpis (praeter A. Coltoni formis raris) legumine septo angusto sed facile observato subuniloculari diversa et hac nota Strigulosis nonnullis (e.g., A. cobrensi) similis, sed stipularum forma cum eis incongrua.—Perennis diffuse adscendens, appresse strigulosa, eaulibus e radicis collo subterraneo 2—4 dm. longis, foliolis oblongis 3—7-jugis omnibus (ut terminali) articulatis, racemis laxis 6-20-floris, floribus parvulis calyce 4-4.5 mm., vexillo carinaque subaequilongis ± 8 mm. longis, legumine pendulo, subsessili, anguste lineari-ellipsoideo sub- recto 2—3 cm. long, obtuse triquetrim compresso, ventre carinato dorso aperte sulcato, valvulis chartaceis strigulosis anguste introflexis septo 0.3—0.6 mm. lato.—Utah: in desert along west side of Comb Wash, 9 miles west of Bluff, San Juan County, May 27, 1961, Cronquist 9123.— Holotypus, NY! isotypi 9 distributuri.

    The Cronquist milk-vetch is a modest astragalus but one of great theoretical interest. It stands apart from all other Lonchocarpi because of its regularly pinnate foliage combined with a subsessile, trigonously compressed pod the cavity of which, unlike that of other members of the section (except rarely in A. Coltoni), is partially divided into two chambers by a narrow septum. In general appearance A. Cronquistii does not suggest the normally ephedroid or at least sparsely leafy Lonchocarpi as much as some members of sect. Scytocarpi or sect. Strigulosi. The habit of growth, subterranean root-crown, sheathing lower stipules, and bicolored leaflets recall some forms of A. (Scytocarpi) flexuosus or A. (Strigulosi) cobrensis, and the trigonous, subunilocular pod also suggests an affinity to the Strigulosi. However, the lower stipules in both these sections are fully amplexicaul and connate opposite the petiole into a cuplike sheath, quite different from those of sect. Lonchocarpi which are united to a vestigial petiole but only about three-fourths amplexicaul. No Strigulosi are known to occur in Utah; they are a southern group, largely Mexican, and none really resembles A. Cronquistii in fine detail. Two small-flowered Scytocarpi are more or less closely sympatric with A. Cronquistii and occur at similar elevations and in like habitats. One of these, A. flexuosus var. Diehlii, has flowers nearly one half smaller and pods, of course unilocular, scarcely half as long. The other, with flowers of about the same size, is A. fucatus, a species common on dunes between Bluff and Mexican Hat; although this resembles the Cronquist milk-vetch closely in habit, it is very different in its bladdery-inflated, gaily mottled pod.

    The affinities of A. Cronquistii are controversial. Judged principally by the pod, it would fit most easily into sect. Strigulosi, but would be anomalous there on account of the stipules. The pod’s trigonous compression can be matched very nearly in A. (Lonchocarpi) nidularius, so that the only feature foreign to the present section (or nearly so; cf. a rare form of A. Coltoni, mentioned below) is the incipient septum in the pod. As a rule the form of the stipules, especially low on the stems, provides a more reliable clue to kinship in Astragalus than do many features of the pod. Stipules have no apparent role in the survival of the species and yield seldom and reluctantly to evolutionary progress, whereas the pod is modified with almost every evolutionary step at the specific level. A septum, whether developed or not in a given species, seems to be latent in the gene-stream of the genus, ready to crop out in the most unforeseen places and, conversely, as abruptly disappearing in particular cases. The Cronquist milk-vetch combines features of sects. Lonchocarpi and Scytocarpi, groups which are certainly close kindred. Selection of the right genes from the nearly sympatric A. (Scytocarpi) fucatus and A. (Lonchocarpi) nidularius, which is found only a little way distant in White Canyon, might produce a plant resembling A. Cronquistii. The ample material is very uniform and cannot be interpreted as a recent hybrid, but the species may be a recombination type in which one primitive character (the septum), latent in the progenitors, has reappeared. In any case A. Cronquistii is so distinct that it must figure as typus of a monotypic subsection.