Dalea exigua

Rupert C. Barneby

22. Dalea exigua Barneby

(Plate XLIV)

Slender, erect annual herbs, 1-4 (4.5) dm tall, strict and monocephalous, or few- branched with strictly ascending to divaricate-incurved, monocephalous branches from below or near the middle, or exceptionally 3-4-stemmed from near the base, the stiff stems purplish at base, green and angled upward, smooth, not or very sparsely gland-punctate, the foliage appearing glabrous but the leaflets charged above, along or near the margins, with a few fine, weak, scattered hairs; leaf-spurs up to 1 mm long; stipules subulate, subherbaceous, 1.5-3 (4) mm long; intra-petiolular glands obsolete; post-petiolular glands very small and pallid, or obscure; leaves 1.5-5.5 cm long, petioled, the rachis narrowly margined, punctate or not, the leaflets of the main cauline leaves 3 or 5, of the upper leaves often only 1, all linear-oblanceolate to -elliptic or narrowly oblong, obtuse to acuminate but always mucronate, (0.5) 1-3.7 (4) cm long, the terminal one longest, the margins ± thickened and elevated, the upper face bright green, the lower paler, punctate; peduncles erect, (2.5) 4-16 cm long; spikes dense (but hardly conelike), shortly ovoid to oblong becoming narrowly ovoid to cylindroid, without petals 5-8 mm diam, the pilosulous axis becoming (0.8) 1.3-4.5 (6) cm long; bracts persistent (falling only with the fruiting calyx), subdimorphic, the lowest 2.5-3.3 mm long, broadly deltate-ovate or rhombic, shortly apiculate, glabrous or nearly so dorsally but ciliolate at base, the interfloral ones narrower, shortly acuminate, membranous-margined at base, pilosulous dorsally and more densely ciliolate, all gland-verrucose dorsally; calyx 3.8-4.3 mm long, silky-pilose with refuscent hairs, the tube 1.9-2.2 mm long, the ribs filiform, brown, the membranous-hyaline intervals eglandular, the triangular-cuspidate to lance-aristate teeth 1.2-2.3 mm long; petals pink-purplse, concolorous, fugacious, the inner ones perched just below separation of the filaments; banner 3.4-4.3 mm long, the oval-ovate blade 1.3-1.6 mm long, 1-1.2 mm wide; wings 1.7-2.3 mm long, the claws 0.3-0.4 mm, the oblong- oblanceolate to obovate, truncate-emarginate blades 1.7-2.3 mm long, 0.9-1.1 mm wide, scarcely auriculate basally; keel-petals 2-2.5 mm long, the claw ± 0.5 mm, the subsymmetrically oblong-oblanceolate blade 1.7-2 mm long, 1.1 mm wide; androecium 4-7-merous, 3.2-4 mm long, with only 3-6 fertile stamens, the longer filaments free for ± 1 mm; pod obovate in profile, ± 2.5 mm long, the style-base lateral just below the apex, the slender prow livid-margined, the valves hyaline in lower 2/3 thinly papery and pilosulous distally. — Collections: 19 (ii).

Open grassy slopes and flats in pine or pine-oak woodland, 1500-2160 m (5000 -7200 ft), forming colonies but local, along and near the crest of northern Sierra Madre Occidental in w. Chihuahua (mpos. Hidalgo del Parral, Cuauhtemoc, Madera) and n.-e. Sonora (mpos. Babispe, Santa Cruz) n. to the sources of the Gila River in s.-e. Arizona (Santa Cruz, Cochise, Greenlee cos.) and s.-w. New Mexico (Grant Co.).—Flowering August to November. — Representative: UNITED STATES. New Mexico: Rusby 86 (NY). Arizona: Gould & Haskell 4100 (UC); Ripley & Barneby 5154 (CAS, NY). MEXICO. Sonora: Thurber 1027 (NY); £ £ White 2725 (ARIZ). Chihuahua: Pringle 1212 (F, MEXU, NY), 1585 (BR, UC, W); LeSueur 706 (ARIZ, F); Ripley & Barneby 13,881 (CAS, MEXU, NY, US); Townsend & Barber 278 (NY, US).

Dalea exigua (frail) Barneby, based on Petalostemon exilis (weakly) Gray, Pl. Wright. 2: 41. 1853. — "Hill-sides, near Santa Cruz, Sonora, Sept.; also near the copper mines, New Mexico, Oct. (995)." —Lectotypus, Wright 995, GH! isotypi, K, NY, UC, US! paratypus, Thurber 945 from Sta. Cruz, GH! — Kuhniastera exilis (Gray) O. Kze., Rev. Gen. 192. 1891. Non Dalea exilis DC., 1825.

This is an inconspicuous, rather weedy dalea, its sparse foliage and narrow heads of minute, vivid pink-purple but fugacious flowers often well camouflaged by the tangle of late summer annuals and grasses among which it delights to grow. Its open forest habitat in northern Sierra Madre is shared by the habitally similar D. filiformis, distinguished by its leaves of exactly three, threadlike, truly hairless leaflets and by looser and shorter spikes of fewer flowers. The rare D. confusa occurs within the range of D. exigua in Chihuahua, at the same elevation but confined to swales and boggy meadows, the only dalea known to require a moist habitat. This resembles D. exigua in habit and foliage, especially in its weakly ciliate leaflets, but these are about four, not two pairs in the larger stem leaves and the structure of the flower (mentioned further under the next entry) is quite different. In number and shape of leaflets D. exigua most closely resembles the southern Mexican D. plantaginoides, but this has quite glabrous foliage and denser, hard and conelike spikes of white flowers.

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.

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