Dalea exilis
Rupert C. Barneby
92. Dalea exilis DeCandolle
(Plate XC)
Prostrate herbs, with several or many slender flexuous microtuberculate stems (1) 1.5-6 (7) dm long arising from the root-crown or from a shortly forked caudex, these simple only when short, usually branching from middle upward or only distally, green or purplish, glabrous or (especially upward) thinly pilosulous with sinuous sub- appressed or weak spreading hairs up to 0.2-0.6 mm long, the spikes mostly terminal to leafy branchlets, the foliage glabrous or nearly so, green or greenish-glaucescent, the leaflets sometimes thinly ciliolate on margins and dorsal keel, smooth above, gland- sprinkled beneath (some glands often exactly marginal and impressed-crenulate); leaf-spurs 0.5-1.4 mm long; stipules narrowly lanceolate to linear-subulate or -caudate, 1.5-5 mm long, thinly pilosulous towards tip; intrapetiolular glands 2 minute impressed; post-petiolular glands small, prominent but mostly blunt; leaves subsessile or shortly petioled, the primary cauline ones 1.5-4.5 cm long, with narrowly green- margined rachis and (4) 5-8 (9) pairs of oblanceolate to oblong-oblanceolate, commonly open-emarginate, rarely short-acuminate, always gland-mucronulate, flat to loosely folded or marginally involute leaflets up to 2.5-6 mm long, the terminal one (of most leaves) very shortly stalked, the leaves of subradical and axillary spurs (when present) smaller and shorter, with mostly 3-5, rarely 2 pairs of smaller leaflets; peduncles (1) 2-7 cm long; spikes incurved to vertical, moderately dense but not conelike, ovoid becoming oblong or oblong-cylindroid, without petals (but including bracts) 7-10 mm diam, the pilosulous axis (0.5) 1-6 cm long; bracts persistent, homomorphic or the lowest (subtending sterile buds) sometimes firmer and narrower than the rest, 3-5 (5.5) mm long, the broadly ovate, obovate, or oblong-obovate, navicular body 2.2-3.7 mm long, in profile 1-1.5 mm wide, pallidly scarious except for the livid keel and a green or livid patch above middle, charged dorsally with many small yellowish blister-glands, glabrous or nearly so, contracted into a subulate, livid, glabrous or thinly pilosulous tail 0.3-1.8 (3) mm long; calyx (3) 3.4-4.4 mm long, pilosulous with ascending hairs up to 0.4-0.6 (0.8) mm long, the tube (measured to dorsal sinus) 2.2-3.1 mm long, the slender ribs green or livid, the hyaline intervals charged with 1 row of tiny (often scarcely visible) honey-colored glands, the orifice strongly oblique, the triangular-subulate or deltate-apiculate gland-spurred and -tipped teeth slightly unequal, the dorsal one 0.7-1.4 (1.6) mm long, the ventral pair a trifle broader; petals bicolored, the banner white with blue-tipped lobes, sometimes gland- sprinkled in the greenish eye, rubescent, the banner and keel sometimes tipped with a small gland, the epistemonous ones vivid blue or violet-blue, perched below middle of androecium (± 1.2-2 mm above hypanthium); banner 4.5-6.2 mm long, the claw (1.7) 2-3.3 mm, the deltate-ovate somewhat hooded blade 2.6-3.5 mm long, 2.4-3.6 mm wide, open at base but the lobes incurved and adherent to form obscure lateral pockets; wings 3.3-4.4 mm long, the claw 1.1-1.7 mm, the blades 2.1-3 mm long, 1.2-1.5 mm wide; keel 4.6-6.3 mm long, the claws 1.4-2.5 mm, the blades 3-4.2 mm long, 1.9-2.5 mm wide; androecium 10-merous, 5-7.6 mm long, the longer filaments free for 1.4-2.4 mm, the connective minutely gland-tipped, the bluish anthers (0.3) 0.35-0.55 mm long; pod 2.5-2.9 mm long, in profile obovate-deltate, the very short style-base at or just below the adaxial corner, the prow filiform, the valves hyaline in lower half, thence thinly herbaceous, finally papery, gland-sprinkled, thinly pilosulous; seed (seldom seen) ± 2 mm long. — Collections: 20 (o).
Open stony slopes, sometimes among brush, along roadsides or in thin pastures, 2100-3500 m, apparently not uncommon in intermontane valleys of the Peruvian Andes from s. Amazonas and s. Cajamarca s. to Junin, extending feebly to the Pacific slope in s. Ancash (prov. Bolognesi) and Lima (prov. Canta, Huarochiri), passing s.-e. along upper Mantaro valley in Huancavelica into D. boliviana. — Flowering March to May. — Representative: Amazonas. Chachapoyas: Wurdack 645 (F, NY, K, UC, US). Cajamarca. Cajamarca: Ferreyra 3169 (US); Celendin: Hutchinson & Wright 5142, 5261 (NY). Ancash. Bolognesi: Ferreyra 5635, 7458 (US). Huaraz: Ferreyra 14,646 (REGINA). Pasco. Daniel Carrion: Macbride & Featherstone 1167 (F). Lima. Huarochiri: Macbride & Featherstone 301 (F). Canta: Mathews 552 (OXF). HuAnu- co. Ambo: (typus of D. peruviana). Huanuco: Macbride 3507 (F). Junin. Tarma: Killip & Smith 21,790 (US); Junin: Killip & Smith 22,028 (US), Soukup 1890 (US). Huancavelica. cf. discussion infra.
Dalea exilis (meagre) DC., Prod. 2: 247. 1825.— "...in Peruvia." — Holotypus, labelled "Perou, Pavon", G-DC! — The specimens from Huanuco, Ruiz & Pavon in 1778-88 (F) are only possibly isotypic . — Parosela exilis (DC.) Macbr., Field Mus., Bot. 4: 103. 1927.
Parosela peruviana Macbr., Field Mus., Bot. 4: 106. 1927.— "Peru: ...Ambo, Dept, of Huanuco, April 5, 1923, Macbride 3193..." — Holotypus (F), not examined; isotypus, US! phototypus, Field Neg. 50,208, F!—Dalea peruviana (Macbr.) Macbr., Candollea 7: 223. 1937.
A diffuse herbaceous dalea with neat green foliage and prolific but small, vivid blue and white flowers, D. exilis can be visualized as either a diminished version of the related but more southern D. boliviana, or alternately as a glabrescent or even glabrous and ampler one of the more northern D. humifusa. Collectively these three species form an almost uninterrupted series of variants extending along the Andes from central Ecuador to Catamarca in Argentina, and might logically be treated as substantial geographic expressions of one species. The extreme forms, however, are so different in gross appearance that it seems more practical to follow tradition and recognize three major divisions at the level of species, always bearing in mind that on the common frontiers of their ranges vexatious morphological intermediates will present a problem of identity. Forms intermediate between D. exilis and D. humifusa are mentioned under the latter species; others linking D. exilis with D. boliviana are known from the Mantaro valley in Huancavelica and from Cuzco. In both these provinces there occur individual plants combining the slender branched habit of D. exilis with flowers in one feature or another too large for that species yet too small for ideal D. boliviana. It is impossible to believe that Tovar 166 (US) from near Conaica in Huancavelica is specifically distinct from the essentially typical D. exilis that occurs in neighboring Junin and Huanuco; yet its calyx is much too large to fit comfortably into my concept of D. peruviana and the plant-body is scarcely different from that of, for example, Cook & Gilbert 322 (US) from Ollantaytambo in the canyon of Rio Urubamba in Cuzco, a plant that I take to be good D. boliviana var. herrerae, a concept that coincides rather neatly with the critically intermediate material.
Variation within D. exilis as defined above is most noticeable in pubescence and size of flower. The smallest flower coincides with the northern limit of the species in Amazonas, where the species most nearly approaches the yet smaller-flowered D. humifusa; the largest, as mentioned already, where its range abuts on that of D. boliviana. Northward the plants are almost glabrous up to the spikes, or at least appear so to the unaided eye; southward the young stems and the leaflets tend to be more or less hairy, usually with very short subappressed trichomes, but sometimes, as in the type-collection of D. peruviana, with weak, relatively long, horizontally spreading ones. These are interpreted as minor variants of a type to be expected in all widely dispersed species of Dalea.
Interpretation of the holotype of D. exilis has presented all students of the genus with a difficult problem, partly because it is rather fragmentary and also immature, but more importantly for this reason: the flower stands near the large extreme admissible to D. exilis, close to the small extreme of D. boliviana, while the foliage might represent either species. Macbride (1943, p. 365, 368) suspected that D. exilis was D. boliviana, but maintained it nevertheless as distinct both from D. boliviana and from D. peruviana, although still known only from the type-collection. The relatively narrow lower bracts seen on one of the two spikes in the Prodromus herbarium, described in the protologue of D. exilis and mentioned repeatedly since — Macbride called them "abnormal" —, are of a type commonly observed in many daleas, especially where some of the lowest flowers are abortive. Such bracts, variously intermediate in form and texture between the upper (interfloral) bracts and the uppermost stipules, are found on a modern collection of D. exilis from Junin (Soukup 1890, US). I have not dissected a flower of holotypic D. exilis and cannot therefore be entirely sure of exact measurements; but the calyx, examined dry, seems altogether too small for genuine D. boliviana and the keel-blades (±4 mm long) are likewise below the normal range for that species. It is perhaps not irrelevant that the most southeasterly point reached by Ruiz and Pavon in the Peruvian Andes was the town of Concepcion in southern Junin, a point in the Montaro valley about 25 km upstream from Huancayo, where D. exilis has been collected several times in recent years. Typical D. boliviana is first encountered well to the southeast, in Ayacucho, and could not, so far as we now know, have been encountered by Pavon (cf. Steele, 1964, map in Appendix).
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:
