Dalea thouini
Rupert C. Barneby
25. Dalea thouini Schrank
(Plate XLVII)
Slender annuals (0.7) 1-3.5 (4.5) dm tall, glabrous to the silky-barbate spikes, when depauperate with 1 erect monocephalous stem, but commonly branching either from below or above the middle, each branch monocephalous, the stems striate but not coarsely angulate, minutely microtuberculate, the foliage bicolored, the leaflets vivid yellowish-green above, blue-green beneath, minutely black-punctate on both sides; leaf-spurs 0.4-1.5 mm long; stipules narrowly lance-acuminate or triangular, 1-3 mm long, with narrow, pallid or papery-castaneous margins; post- and intra- petiolular glands minute or obsolete; leaves (0.6) 1-4 cm long, shortly petioled, with narrowly margined rachis and 2-4 (5) pairs of oblanceolate to narrowly obovate, emarginate, flat leaflets (3) 5-12 mm long; peduncles (0.5) 1-9 cm long; spikes moderately dense, narrowly ovoid to cylindroid, without petals (7) 8-10 cm diam, the pilosulous axis (5) 9-35 mm long; bracts persistent, 2.7-4.5 mm long, dimorphic, the lowest ovate-elliptic to ovate and acute, dorsally glabrous, glabrate beyond the middle, or rarely thinly pilosulous, within densely white-silky, the rest narrower, lance- acuminate or -caudate, pilosulous both sides, all livid-black or -green, obscurely or minutely gland-sprinkled; calyx (3.1) 3.3-4.2 mm long, silvery-pilose with ascending, finally spreading hairs, the tube 1.5-1.9 mm long, recessed behind the banner, the subfiliform ribs blackish, the hyaline intervals charged with 1 row of ± 3 minute glands, the teeth narrowly subulate from a deltate-triangular base, (1.5) 1.7-2.3 mm long, gland-spurred, plumose; petals dull purplish-blue, all sprinkled and the banner often tipped with tiny glands, the banner longest, at full anthesis overtopping the epistemonous petals, these perched ± 0.8-1 mm above the hypanthium, the inner pair adherent by narrowly overlapping margins, slightly shorter than the filaments; banner 3.6-4.2 mm long, the claw 1.3-1.6 mm long, the erect, broadly ovate, shallowly emarginate blade 2.3-2.7 mm long, 1.8-2.3 mm wide; wings (1.7) 2.2-2.8 mm long, the claw 1.3-1.6 mm, the oblanceolate, scarcely oblique blade (1.2) 1.4-2 mm long, 0.7-0.8 mm wide; keel-petals 2.7-3 mm long, the claw 0.8-1 mm, the narrowly oblong-oblanceolate, scarcely auriculate blades 1.8-2.3 mm long, 0.6-0.7 mm wide; androecium 10-merous, 3.6-4.7 mm long, the longer filaments free for 0.5-0.8 mm, the connective minutely gland-tipped, the anthers 0.25-0.3 mm long; pod ± 2.5 mm long, obliquely obovoid, the style-base lateral, hyaline in lower 2/3, thinly papery distally, the blackish, filiform prow pilosulous; seed ± 2 mm long; 2n = 14 (Mosquin).— Collections: 15 (vi).
Cool rocky slopes and moist flats or hollows among bunch-grass in the pine and pine-oak belts, mostly 2530-3330 m (7600-10,000 ft), but in Morelos (Sierra de Tepoztlan) descending on pedregal as low as 1870 m (5600 ft), local but forming colonies, known from two widely disjunct areas, one on the divide between Mexico (Estado and Distrito Federal) and Morelos (Sierra de las Cruces, Serrania de Ajusco, and vicinity), the other on or near the divide of the Sierra Madre Occidental in w.- centr. Durango (El Salto and w.-ward). — Flowering September to November.- Representative: Morelos. Tepoztlan: Ripley & Barneby 14,553 (CAS, NY); Huitzilac: Ripley & Barneby 14,526 (CAS, DAO, MEXU, NY, US). Mexico (D. F.). Delegation de Tlalpan: Matuda 21,947 (MEXU, NY). Mexico (Edo.). Ocuilan de Arteaga: Matuda 25,589 (MEXU, NY); Toluca: Pringle 5256 (ENCB, MEXU, US). Durango. El Salto: Ripley & Barneby 13,975 (BM, CAS, GH, MEXU, MICH, NY, US), 14,169 (CAS, DAO, MEXU, NY, US).
Dalea thouini (Andre Thouin, 1747-1824) Schrank, Pl. Rar. Hort. Monac. 1: 9, cum tab. 1817 ("Thouin"). — "Missa sunt semina a celeb. Thouinio..." — Named from cultivated specimens of unstated origin, but presumably first grown in Paris, doubtless from seeds collected in Mexico. — No spm. found at M, P, or Z, the cited plate accepted provisionally as holotypus. — Parosela thouini (Schrank) Rydb., N. Amer. Fl. 24: 78. 1920. P. leporina var. thouini (Schrank) Macbr., Contrib. Gray Herb. New Ser. 65: 17. 1922.
In its annual root, glabrous foliage, and narrow, softly gray-silky spikes of inconspicuous flowers, D. thouini resembles the much commoner D. leporina and has been unnecessarily confused with it. It differs in having only 2-4 (not 8-many) pairs of leaflets even in the primary cauline leaves, and especially in its persistent interfloral bracts, livid-black but almost glandless externally and densely white-silky within. Internally pubescent bracts are found here alone among annual species of the genus. Few leaflets and persistent bracts are features common to D. thouini and the more nearly related D. polygonoides, but the bracts of the latter are glabrous within and charged outside with a few exceptionally large and lustrous blister-glands.
I have followed Rydberg’s interpretation of the nomenclature, which may nevertheless need revision if any original material, grown either by Thouin at Paris or by Schrank at Munich, can be located. Schrank’s rather crude plate and short description suggest no other known species, but do not show the decisive critical features of the species here treated. I find no record of the introduction of D. thouini to European gardens, but growing as it does along the old coach road over the mountains between Mexico and Cuernavaca it has been within easy reach of travellers from early times.
The bicentric dispersal of D. thouini is rather remarkable for an annual herb, although it is nearly matched by that of the also annual D. obreniformis. Intermediate stations for these two species, as also for races of D. urceolata intermediate between var. urceolata and var. tripetala, are to be sought in southern Sierra Madre Occidental and in the mountains of Jalisco.
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:
