Dalea nelsonii
Rupert C. Barneby
15. Dalea nelsonii (Rydberg) Barneby
(Plate XXXIX)
Perennial, herbaceous or weakly suffrutescent, from a woody root and short caudex, glabrous to the spikes, the diffuse and radiately ascending, chestnut-purple (rarely green) stems (3.5) 4-9 dm long, verruculose throughout with many small, round, orange or purple glands, simple at base, paniculately branching from near or above the middle, the foliage green, the leaflets punctate beneath (the glands rarely visible from above), their margins commonly purplish; leaf-spurs 0.6-1.5 mm long; stipules narrowly linear-caudate, 3-8 mm long, livid, sparsely glandular; intrapetiolular glands 2, minute; post-petiolular glands conic, prominent; leaves 1.5-4.5 (5) cm long, shortly petioled or subsessile, the rachis very narrowly margined, the leaflets 9-18 pairs, elliptic to narrowly elliptic-oblanceolate, minutely emarginate, keeled dorsally, involute or loosely folded, 1-6.5 mm long; peduncles terminal to the main axis and to all its branches, 1-11 cm long; spikes dense, narrowly conic becoming cylindric, without bracts or petals 8-14 mm diam, the glabrous or puberulent axis becoming (1) 1.5-9 cm long; bracts persistent, narrowly lance-caudate, 3-6.5 mm long, livid, sparsely glandular, all glabrous or the upper ones thinly pilosulous dorsally, the lowest sometimes minutely ciliolate at base; calyx 3.7-4.9 mm long, early becoming a little tumid and oblong-ellipsoid, glabrous except for a few weak, spiral hairs distally but the teeth silky-pilose within and the mouth therefore ciliate, the tube (measured to a dorsal sinus) 2.5-3.6 mm long, deeply recessed behind the banner, the ribs subfiliform, livid-nigrescent, the membranous, plane intervals charged with many small, yellowish blister-glands arranged in ± 2-3 vertical ranks, the livid, subulate or triangular-subulate teeth unequal, the dorsal one longest and narrowest, 0.8-1.6 mm long, the ventral pair broader and commonly shorter; petals bicolored, bright lavender-blue and white, the banner white with blue tip, the white part rubescent in age, all eglandular, the epistemonous ones perched just below, or the inner pair a trifle above separation of the filaments, about half-way between hypanthium and anthers; banner 5-7.8 mm long, the claw (2) 2.8-4 mm, the ovate, shallowly emarginate, almost erect blade 2.9-4.3 mm long, 2.2-3.8 mm wide; epistemonous petals 3.5-5.1 mm long, all alike but the inner pair sometimes a little larger, the blades elliptic-oblanceolate to oblong- obovate, 2.9-4.2 mm long, 0.8-1.9 mm wide, obliquely contracted at base into a claw 0.6-1 mm long; androecium 10-merous, (5.3) 6-8.5 mm long, the filaments free for (2.8) 3-4.2 mm, the connective gland-tipped, the pale yellow anthers 0.45-0.55 mm long; pod 2.5-2.8 mm long, obovoid in profile, the short style-base latero-terminal, the ventral crest and prow very slender, the valves hyaline except at the thinly herbaceous, green, sparsely microglandular tip; 2n = 7 II (Mosquin). — Collections: 8 (ii).
Open stony and grassy hillsides in oak-pine forest, sometimes on volcanic tuff, 1800- 2460 m (± 6000-8200 ft), local but forming colonies, on and near the crest of Sierra Madre Occidental from the headwaters of Rio Verde in s.-w. Chihuahua (± 26° 20' N) s.-w. to the sources of Rio Acaponeta in w. Durango (± 24° 45' N).— Flowering August to November. — Material: Chihuahua. Balleza: Sierra Chinatu, Correll & Gentry 22,952 (RENNER). Guadelupe y Calvo: Nabogame, Gentry, Correll & Arguelles 17,972 (RENNER, US). Durango.— P. Ibana Garcia 370 (US). Ciudad Durango: 38 mi w. of Durango, Ripley & Barneby 13,961 (CAS, DAO, NY, MEXU, MICH, US); 51 mi. w., Ripley & Barneby 14,003 (NY); 24 mi. e. of El Salto, Mosquin 6828 (NY); 22 mi n.-e. of El Salto, G. & F. Ownbey 2001 (MICH).
Dalea nelsonii (Rydb.) Barneby, comb. nov., based on Thornbera nelsonii Rydb., N. Amer. Fl. 24: 120. 1920 ("Nelsonii"). — "Type collected sixty miles south of Guadelupe y Calvo, Chihuahua [perhaps really south of the state line in Durango], August [20], 1898, E. W. Nelson 4790..." — Holotypus, US! isotypus, NY!
This is a relatively showy and decorative dalea, the only blue-flowered species of the Thornbera type known to occur in its short segment of the Sierra Madre. The warty, usually castaneous stems of the adult plant are numerous and freely branched, radiating from a short caudex and fringed all around the loose-woven mat of foliage with a multitude of tasselled spikes. Although the individual flower is small, several successive ranks of them bear expanded petals, older or younger, at the same time, forming a band of color around the spike of calyces. West of Durango D. nelsonii shares the pine-oak forest with the habitally similar D. cyanea, a species coincidentally similar in its blue or blue and white petals and asymmetrically cleft calyx-tube, but readily distinguished by its flower of the parosela type, with anthers concealed in a conventional keel, or if these are past by the few (4-8, not 9-18) pairs of leaflets.
In the accompanying plate the petal-sockets are shown (fig. 10) in their usual situation, just a trifle below the point of separation of filaments. There is some variation, however, in the depth of the filament tassel, the sinuses sometimes being recessed back up to 0.2 mm below the sockets so that the petals seem to issue from little eminences on the back of alternate stamens.
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:
