Dalea obreniformis
Rupert C. Barneby
20. Dalea obreniformis (Rydberg) Barneby
(Plate XLIII)
Slender annual herbs, commonly (1.5) 2-6, sometimes only (0.7) 1-2 dm tall, the stiff, prominently ribbed and angled stems usually branched below the middle, sometimes also distally, the main axis (rarely simple) erect, the lateral ones divaricate and ascending, either glabrous below the spikes or minutely pilosulous beyond the middle, sparsely micro-tuberculate distally but otherwise smooth, the glabrous foliage bicolored, the leaflets green above, pallid and livid-dotted beneath; leaf-spurs 0.4-1 mm long; stipules narrowly subulate-caudate or sublinear, becoming stiff and dry, 1.5-5 mm long, often minutely ciliolate; intrapetiolular glands minute or seti- form; post-petiolular glands small, prominent; leaves (1)1.5-4.5 cm long, shortly petioled, the rachis narrowly margined, grooved ventrally, not or scarcely punctate, the leaflets (2) 3-9 pairs, oblong-obovate to narrowly oblanceolate, obtuse or emarginate, submembranous, flat or loosely folded, gland-crenulate near apex, 3-13 mm long, the terminal one (nearly always sessile) slightly longer than the last pair; peduncles (beyond the first) all terminal to branchlets, 1-9 (11) cm long; spikes densely many-flowered, conelike when young, the shorter ones ovoid becoming oblong, the longer ones becoming cylindroid, without petals 5-7 mm diam, the pilosulous axis (0.5) 1-4 cm long; bracts persistent, embracing the calyces, subdimorphic, the lowest ones broadly obovate-truncate and abruptly caudate (1.7) 2.5-3.5 mm long, the tail half as long to nearly as long as the dorsally glabrous or subglabrous body, the rest truncately flabellate, obcordate, or inversely reniform, keeled dorsally, 1.5-3 mm long, the tail reduced to a mucroniform appendage in the apical notch, these often thinly pilosulous dorsally and ciliolate, all along the keel and above the middle livid and charged with orange or pale yellow blister-glands, the margins broadly hyaline; calyx thinly pilosulous externally over the whole surface or only along the back, ciliate at mouth, 2.1-3.1 mm long, the tube at first conic-campanulate, later turgid and ovoid, 1.6-2.2 mm long, deeply recessed behind the banner, the subfiliform ribs livid (at least beyond the middle), the hyaline intervals either eglandular or charged with a row of 1-3 minute glands, the triangular or ovate-triangular, mucronate, minutely gland-spurred, nigrescent teeth subequal or slightly unequal in length, the dorsal one either longest or shortest, 0.5-1.2 mm long; petals all vivid blue, eglandular, the wings and keel perched just below separation of the filaments, the keel-petals sometimes a trifle smaller than the wings; banner 2.5-3.7 mm long, the claw 1.2-2 mm, the triangular-ovate blade 1.2-2 mm long, 1.2-1.5 mm wide; wing and keel-petals 1.1-1.8 mm long, the wings obovate-oblong, the keel-blades broadly obovate, ± oblique, the claw minute; androecium (2.4) 2.7-3.6 mm long, 5 (6)-merous, the filaments free for (0.5) 1.6-1 mm, the connective gland-tipped, the exposed but not exserted anthers blue, ± 0.3 mm long; pod obovoid, 2-2.6 mm long, the style-base latero-terminal, the valves hyaline in lower 2/3, thinly papery distally, livid along the dorsal crest and filiform prow, finely pilosulous distally but eglandular; seed (1.1) 1.3-1.7 mm long; 2n = 28 (Mosquin). — Collections: 20 (x).
Colonial in open pine or pine-oak woodland, descending on malpais into the scrub belt, 1680-2460 m (± 5600-8200 ft), apparently of bicentric dispersal: locally common and rather frequent in the Transverse Volcanic Belt, from Sierra de Tepoztlan, Morelos w. to the latitudes of Volcan Tancitaro in Michoacan; and on or near the crest of Sierra Madre Occidental about the headwaters of Rios Mayo, Fuerte and Petatlan (at 1800-2160 m) in s.-w. Chihuahua and adjoining Sinaloa (Sa. Surutato); to be sought in Jalisco, Nayarit, and Durango. — Flowering July to December, mostly from September onward in its southern range— Representative: Chihuahua: Gentry 1951 (ARIZ, F, K, MEXU), 2704 (ARIZ, F, K, MEXU, US). Michoacan: Ripley & Barneby 13,429 (CAS, MEXU, NY, US), 14,835 (CAS, DAO, NY, US), 13,406 (CAS, K, MEXU, MICH, NY, US); Hinton 15,561 (G, K, NICH, NY, RENNER, UC, US, W). Mexico: Hinton 8352 (ARIZ, F, K, MEXU, NY); Ripley & Barneby 13,766 (CAS, MEXU, NY, US). Morelos: Ripley & Barneby 14,535 (DAO, MEXU, NY, US), 14,546 (CAS, MEXU, MICH, NY, US).
Dalea obreniformis (Rydb.) Barneby, comb. nov., based on Petalostemum obreniforme (inversely kidney-shaped, of the bracts) Rydb., N. Amer. Fl. 24: 130. 1920."Type collected at the base of Mt. Mohinora, Chihuahua, 8 miles from Guadelupe y Calvo, August, 1898, E. W. Nelson..." — Holotypus (Nelson 4835), US! isotypi, K, NY!
This is an inconspicuous, rather weedy little plant, but a most interesting one. It is the only annual Dalea known to be tetraploid, and in several aspects of its gross morphology is highly specialized. Notable features are the dense but narrow spikes of tiny, vivid blue flowers, the cordate or inversely reniform bracts of a livid or blackish color folded around the calyces, and an androecium reduced to five or less often six members. Although it was originally described as a Petalostemum, because of the few stamens, D. obreniformis is much more closely related to D. cliffortiana, but easily distinguished from that and all related species by the retuse bracts and concolorous petals of vivid blue. The foliage most nearly resembles that of D. dipsacea, but the terminal leaflet is in that species always raised beyond the last pair, in D. obreniformis almost always sessile.
The distribution of D. obreniformis as known at present is notably discontinuous, a formidable gap separating the populations in Sierra Tarahumare near latitude 26° N and those in the mountains of south-central Mexico at about lat. 19° N. Intermediate stations are to be expected, but even if none are found there seems to be no morphological evidence of distinct races having developed in the two areas. In central Mexico the plants are often browsed, and Gentry reports them "eaten by cattle" on the upper Rio Mayo.
References: [Article] Barneby, Rupert C. 1977. Daleae Imagines, an illustrated revision of Errazurizia Philippi, Psorothamnus Rydberg, Marine Liebmann, and Dalea Lucanus emen. Barneby, including all species of Leguminosae tribe Amorpheae Borissova ever referred to Dalea. Mem. New York Bot. Gard. 27: 1-892.Multimedia:
