147.  Dalea pogonathera Gray

(Plate CXXXIII)

Low perennial herbs from a forking orange root and shortly branched or pluricipital knotty caudex, glabrous up to the calyx, the several or numerous, decumbently radiating to weakly ascending, pallid, sparsely glandular but scarcely verruculose stems (0.4) 0.7-3.5 dm long, simple or branched at 1-2 (4) nodes above the middle, each axis monocephalous, the foliage smooth, the leaflets yellowish-green above, glaucous and livid-punctate beneath; leaf-spurs 0.1-0.8 mm long; stipules narrowly triangular-acuminate to subulate or linear-attenuate, (0.7) 1-2.6 mm long, becoming papery and brownish but the margins pallid-scarious, especially on the side opposite the petiole; intrapetiolular glands 0; post-petiolular glands prominent, obtuse, often crateriform when dry; leaves (0.4) 0.8-2 (2.5) cm long, short-petioled, with punctate, narrowly margined rachis and (1) 2-3 (4) pairs of narrowly oblanceolate to narrowly oblong-elliptic or linear-oblong, emarginate, thick-textured, marginally elevated or loosely folded leaflets (1.5) 2-10 mm long; peduncles 0.5-4 cm long; spikes relatively loose, (8) 12-40-flowered, the flowers becoming ± 2-3-ranked when pressed and not concealing the glabrous axis, without petals or androecia 9-18 (20) mm diam, (0.5) 1-8 cm long; bracts persistent, embracing the calyx, broadly ovate, cucullate and truncate at base, abruptly short-acuminate or mucronate at apex, 3-6 mm long, 3.2-5 (5.5) mm wide, in the lower 2/3 membranous-margined, dorsally keeled and the herbaceous middle pallid- or pinkish-glaucescent and gland-tuberculate; calyx (5) 5.2-10.5 mm long, the densely villosulous tube 2.6-3.4 mm long, the ribs filiform becoming prominent, the submembranous intervals charged with 1 row of 4-7 small, pallid or honey-colored glands, the deltate- or broadly triangular-aristate teeth 1.9-7.2 mm long, varying from 1 mm shorter to 2.8 (4) mm longer than tube, plumose with spreading spiral villi up to 0.8-2.2 mm long; petals pale or vivid violet-purple, glandless, or the banner rarely charged in the pallid or greenish, finally rubescent eye with 1-2 small glands, the epistemonous ones perched near middle of androecium; banner (4.5) 4.8-7.8 mm long, the claw (2.5) 3.3-4.7 mm, the broadly ovate, emarginate, deeply cordate blade 2-3.6 mm long, 2.4-4 mm wide; wings 2.4-4.2 mm long, the claw (sometimes shorter than the auricle, appearing lateral) 0.3-1.2 mm long, the obliquely ovate or oblong-ovate blade 2.3-3.9 mm long, 1.2-2.1 mm wide; keel 4.2-7 mm long, the claws 0.8-1.8 (2.4) mm, the oblong-elliptic or obovate blades (3.4) 4-5.8 mm long, 1.9-3.1 mm wide; androecium 9- or 10-merous, (6.5) 7.5-10.5 mm long, the longer filaments free for 1.7-3 mm, the connective glandless, the pallid anthers (0.4) 0.5-0.7 mm long; pod 2.8-3.5 mm long, glabrous and hyaline in the lower 3/4, thence firm and densely ascending-pilosulous, the prow broad, grooved between the prominent margins; seed castaneous or mahogany-brown, smooth and lustrous, 1.9-2.4 mm long.

The two purple-flowered Pogonatherae, D. pogonathera and D. lasiathera, are closely related and habitally very similar, the pale, sparsely glandular stems, glaucous punctate foliage, and broadly membranous-margined, gland-dotted bracts being essentially identical. Rydberg (1920, p. 70) separated them by means of calyx-measurements, attributing to D. lasiathera teeth much shorter, to D. pogonathera teeth as long or longer than the tube. As a result some of the small-flowered Texan forms of D. pogonathera var. walkerae were wrongly referred to D. lasiathera. Because of the great variation in size of the flower encountered in D. pogonathera, a more complex formula is required for a really effective key. It is remarkable that the range of D. lasiathera lies entirely within that of D. pogonathera and that the two species can exist side by side without any sign of introgression or blurring of specific lines. It is interesting, nevertheless, that on Edwards Plateau where D. lasiathera is most abundant D. pogonathera is less often encountered; conversely outside the Plateau, where D. pogonathera is the commonest, almost ubiquitous dalea, the stations of D. lasiathera are far and few.

The range of D. pogonathera extends from sea-level on the Gulf Coast up to nearly 1900 m on the Mexican Plateau and to similar elevations in Arizona. It is found in a great variety of habitats and on soils of diverse origins, but exhibits little structural variability except in size and relative proportions of the calyx and petals. At one extreme the flower spike (without petals) may measure 2 cm, at the other barely 1 cm in diameter; and the dorsal calyx-tooth varies from 1 mm shorter up to 4 mm longer than the tube. The size of flowers is well correlated with dispersal and permits an arbitrary division of the material into a lowland, eastern, small-flowered var. walkerae virtually confined to the Rio Grande valley downstream from the mouth of the Pecos and the Texan Gulf Prairie, and a large- flowered, upland and western var. pogonathera. In the foothills of Sierra Madre near Monterrey, and in east-central Coahuila and adjoining Texas, the species passes through a zone of transition where intermediate forms predominate. Here the division of the species into two varieties on the basis of a single character (dorsal calyx-tooth more or less than 4 mm long) is revealed for what it is, a taxonomic artifice which, nevertheless, is justified in practice over an immense tract of territory. The holotype of D. pogonathera stands unfortunately among the specimens which are essentially intermediate. It is here interpreted, following Turner (1959), as belonging to the large-flowered, upland series, the longest calyx-tooth reaching 4 mm, and the hairs at mouth of the calyx being relatively long (± 1.5 mm). The type-station, somewhere in the Sierra Madre foothills near Monterrey, is situated near the belt of intergradation just mentioned.