Dalea escobilla

  • Title

    Dalea escobilla

  • Author(s)

    Rupert C. Barneby

  • Scientific Name

    Dalea escobilla Barneby

  • Description

    62.  Dalea escobilla Barneby

    (Plate LXVIII)

    Tall herbs, glabrous to the inflorescence, with 1-few virgately erect and assurgent stems from carrotlike root, at anthesis 7-10 dm tall, the stems striate, smooth or obscurely glandular distally, sparsely leafy, above the middle branching into an almost leafless panicle of spikes; leaf-spurs very small; stipules deltoid, very small, livid and subcarnose, becoming dry and deciduous; main cauline leaves 3-8 cm long, with very narrowly margined rachis and 9-17 pairs of broadly oblong to ovate-oblong, obtuse to emarginate, flat leaflets 3-6.5 mm long, these smooth and green above, gland- punctate beneath; peduncles slender, 2-10 cm long; spikes short and rather loose, (10) 15-30-flowered, the densely villosulous axis becoming 6-12 mm long; bracts early deciduous, ovate-acuminate, ±1-4 mm long, ciliolate at base and apex, glabrous and glandular dorsally; calyx 2.7-3.3 mm long, glabrous externally up to the densely ciliolate orifice, the tube 1.9-2.2 mm long, the ribs very slender, black or livid, the membranous intervals charged with scattered golden glands, the broadly triangular to deltate, apiculate and gland-spurred teeth unequal, the dorsal one longest, 0.9-1.2 mm long, the orifice subsymmetrical; petals bicolored, the banner opening whitish sometimes with purple tip and lobes but fading reddish, the inner rose-purple, elevated 0.7-1.2 mm above the hypanthium rim, the banner gland-sprinkled in the eye but no petals gland-tipped; banner 4.2-4.5 mm long, the claw 1.5-2.2 mm, the deltate-cordate blade hooded and obtuse at apex, closed at base into a shallow cornet, 3.1-3.3 mm long, ± 3 mm wide; wings ± 4.8 mm long, the claw 1.7 mm, the elliptic blade 3.6-4 mm long, 2 mm wide; keel ± 5.3 mm long, the claws ± 1.6 mm, the blades 4-4.4 mm long, 2.5 mm wide, united by their outer edges; androecium 10- merous, 5.7-6.5 mm long, the longest filament free for 1.8-2 mm, the connective gland-tipped, the anthers 0.5-0.65 mm long; pod obovoid, strongly compressed, ± 2.5 mm long, thick-crested dorsally, the ventral keel and prow subfiliform, the valves hyaline in lower half, thence thinly papery, glandular, pilosulous; seed ±1.7 mm long. — Collections: 2 (o).

    Sunny openings in oakwoods, sometimes in "thin soil overlying pumice", 10001700 m (3330-5660 ft), known only from the slopes of Cerro de San Juan, s.-w. of Tepic, Nayarit. — Flowering September onward. — Material examined: cf. below.

    Dalea escobilla (the vernacular name) Barneby, sp. nov., D. polystachyae (S. & M.) Barneby et D. mcvaughii Barneby affinis, forsan huic propior, ab ilia calycis extus glabri tantum ad orem brevidentatum intus sericeo-ciliolati dentibus triangulari-deltatis ad 0.9 1.2 (nec 1.7-2.8) mm longis, a D. mcvaughii quoad calycem extus nudum simili imprimis foliolis foliorum majorum (more D. polystachyae) numerosis (9-17 nec 7-9-jugis), spicis laxioribus paucifloris, calycisque dentibus brevioribus statim separata. Herbacea elata univel paucicaulis infra spicas glaberrima, habitu foliisque multifoliolatis D. polystachyam simulans. — Nayarit: sunny opening in woods, 1000 m, Cerro de San Juan; w. of Tepic, Sept 19, 1926, Ynez Mexia 704. — Holotypus, NY; isotypi, BM, CAS, G, GH, MICH, UC, US.-Ibid., Pennell 19,979; paratypi, GH, US.

    This species and the next in order, D. mcvaughii, together differ from other known Pectinati in the externally glabrous, lustrously membranous calyx furnished around and within the orifice with a dense fringe of short silky hairs. They are a closely related pair, so far as known vicariant in dispersal on well-isolated mountain ranges forming part of the western arm of the Transverse Volcanic Belt, and differ most notably in number of leaflets, these being numerous (mostly 10-17 pairs) and also small (3-6.5 mm) in D. escobilla, relatively few (7-9 pairs) and larger (5-11 mm) in D. mcvaughii. The calyx- teeth of D. escobilla are a little shorter, a difference that may well disappear as more collections become available for study, and its spikes seem to be both looser and fewer-flowered. The collective range of the two species lies within that of the wisely dispersed and closely related D. polystachya (S. & M.) Barneby, the flower of which is essentially similar except that the calyx is hairy from the base upward. In the number and size of leaflets D. escobilla and D. polystachya are alike, but the calyx-teeth of D. escobilla are absolutely and decisively shorter (0.8-1.2 not 1.5-2.8 mm long). If the pubescence-character of the calyx, always under suspicion in Dalea, were disregarded in this case, D. escobilla would be accomodated without strain within an only slightly enlarged concept of D. polystachya. It would then become difficult to exclude D. mcvaughii, despite its few leaflets, and this would lead in turn to an altogether unwieldy and unrealistic taxonomy. It seems likely that D. mcvaughii and D. escobilla are indeed recent derivatives of D. polystachya, perhaps not ideally characterized as yet but (until we have evidence to the contrary) abruptly and visibly different from it and from each other.

    The term escobilla, little broom, is applied to many Mexican daleas, in the first place to those which furnish the flexible but tough, twiggy stems that are tied in bunches and, fixed to a pole, make serviceable besoms, but ultimately becomes a generic term. Mexia records the usage for this species in Nayarit.