Dalea humilis G.Don
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Authors
Rupert C. Barneby
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Authority
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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Family
Fabaceae
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Scientific Name
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Type
"Native of Mexico. Dalea herbacea Sesse & Moc. ms." —Holotypus, formerly in herb. Lambert., not known to survive. Neotypus, labelled "Dalea herbacea", Herb. Sesse & Mocino No. 2665, MA! isotypi, F, and (ex herb. Shuttleworth. via Pavon) BM!
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Synonyms
Dalea herbacea Moc. ex Sessé & G.Don, Dalea inconspicua S.Schauer, Parosela inconspicua (S.Schauer) Rose, Dalea ervoides Benth. ex Hemsl., Parosela ervoides (Benth. ex Hemsl.) Rydb., Dalea barrancae M.E.Jones
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Description
Species Description - Annual herbs from subfiliform roots, variable in stature, the primary axis erect only when depauperate and crowded, usually branching from near base and the diffuse, assurgent, or prostrate lateral stems surpassing the primary one, remaining simple or few-forking upward, all striate, eglandular, 0.5-4 dm long, pilose like the leaves with narrowly or widely spreading-ascending spiral hairs up to 1-3 mm long, the leaflets sometimes only thinly so and greenish; leaf-spurs less than 1 mm long, often subobsolete; stipules linear-lanceolate or -caudate, (2) 3-8 (11) mm long, herbaceous above immediate base, gland-tipped; intrapetiolular gland 1, spiculiform; post-petiolular glands 0 or minute and immersed; leaves petioled, the main cauline ones (1) 2-6 cm long, with obscurely margined, eglandular rachis and (1) 2-3 (4) pairs of linear- elliptic to ovate-elliptic, acute, gland-mucronulate, flat or loosely folded leaflets (2) 3-16 (18) mm long, the odd one longest and shortly distant beyond the last pair; peduncles mostly appearing leaf-opposed, slender, 2-8 cm long, either erect or divaricate from the stem and incurved under the spike; spikes relatively loose, the calyces nearly contiguous but not closely imbricated, 4-many-flowered, ovoid to cylindroid, without petals (but including bracts and pubescence) (6) 8-16 (17) mm diam, the axis becoming (0.2) 0.4-4 (5) cm long; bracts deciduous only with the ripe calyx and pod, ovate- to narrowly lance-acuminate, (2) 3-7 (8) mm long, pallidly membranous- margined at base, herbaceous distally, dorsally pilose and often minutely yellow- glandular; calyx sessile or almost so, 3.2-5.4 mm long, pilose externally with ascending spiral hairs, the tube 1.8-2.5 (2.7) mm long, recessed behind the banner, the ribs prominent, the membranous intervals eglandular or charged with 1 row of 1-3 minute transparent glands, the teeth triangular-subulate, gland-tipped, (1.2) 1.5-3.1 mm long; petals variably (indecisively) colored, the banner whitish or pinkish, the epistemonous ones flesh-pink or yellowish, sometimes clearer rose-pink or purplish, perched near or slightly above middle of androecium; banner 3.5-4.8 (5) mm long, the claw 1.8-3.2 mm, the deltate-cordate, rarely rhombic-ovate blade 1.4-2.5 mm long; wings (2.2) 2.5-3.2 mm long, the claw 0.2-0.5 mm, the oblong-elliptic blade (2) 2.2-2.8 mm long, 0.9-1.4 mm wide; keel 2.4-3.4 (3.7) mm long, the claws 0.4-0.9 mm, the obovate blades 2.2-2.6 (2.9) mm long, 1.2-1.6 mm wide; androecium 10-merous (one stamen often barren), 3.7-6 mm long, the longer filaments free for 0.6-1.2 mm, the anthers dark blue, 0.2-0.3 mm long; pod deltate in profile, the sutures filiform, the valves hyaline and glabrous in the lower 2/3, thence thinly papery, pilosulous, eglandular; seed brownish-olivaceous smooth, 1.4-2.1 mm long; n = 7 II (Spellenberg, 1973).—Collections: 68 (xvii).
Distribution and Ecology - Plains, hillsides, in grassland, thorn-scrub, and degraded woodlands, becoming weedily abundant and densely colonial in disturbed soils along highways and in milpa, 1150-2500 m (3850-8325 ft), common almost throughout the Lerma-Santiago valley upstream from s. Nayarit, extending freely into Valley of Mexico and adjoining s. Hidalgo, n.-w., perhaps only as a roadside weed, into centr. Durango; again common at and near the lower edge of the oak-belt around the e. periphery of the Balsas Depression, from w. Michoacan to Puebla (where crossing feebly e. to the upper Papaloa- pan basin) and Guerrero, and s.-e. into centr. Oaxaca; apparently disjunct in highland Guatemala (Huehuetenango), but possibly not native there. — Flowering August to January.
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Discussion
(Plate CXXXI)
This is a truly weedy dalea, delighting in disturbed soils along roads and paths, where the plants often grow so thickly together in a tangle of diffuse thready stems as to exclude all but the rankest competitors. It is easily distinguished from compatriot annuals by the combination of pilose vesture, few (mostly 2 or 3) pairs of expanded, sharp-pointed leaflets, and leaf-opposed peduncles, these of course structurally terminal to the axis of origin but surpassed by the axillary shoot that follows. The tiny petals are dimly pinkish or purplish, sometimes suffused with a dilute yellow tint; often they are concealed by the pilose calyx-lobes, and even when expanded are soon thrown off. In consequence the epithets humilis and inconspicua are descriptive. Because of its dowdy facies D. humilis is passed over by most collectors and actually much commoner than the herbarium record suggests.
Variation in the species is considerable, not only in stature but more especially in size of the individual bract and calyx, in absolute and proportionate lengths of calyx-tube and teeth, and in size of the petals, the full range of which is only suggested in the accompanying plate. Stature of itself has no taxonomic significance, the plant yielding with equal readiness, whether large or small-flowered, to accidents of environment. An extreme phase with one or few filiform stems bearing a few narrow heads of some 4- 10 flowers appears distinctive when separated out on a herbarium sheet, but is often no more than a starveling extracted from a smothering crush of its own kind. A favored individual from the same roadside ditch can have many decumbent stems issuing from the primary axis, each bearing a succession of divaricate peduncles bearing plumply ovoid or cylindroid, clover-like heads of many flowers. The features within the inflorescence already mentioned as variable are at least loosely correlated, and whole colonies are often encountered that are nearly uniform in flower- and bract-size. Thus there is some ground for recognition of two infraspecific taxa corresponding with Rydberg’s Parosela ervoides and P. inconspicua, respectively short and long in bract and teeth. The difficulty about such a treatment is twofold: the forms as envisaged by Rydberg are widely sympatric and of nearly the same total range; and there are now many collections ambiguous between the idealized norms. A particularly notable example of sympatric forms of D. humilis, one coarsely leafy and heavy-headed, the other of the slender ervoides type, is documented by Ripley & Barneby 14,512 (NY, 2 sheets), collected on a grassy hill below the knobs at Tepoztlan in Morelos. In this station the two types occurred in a mixed population under uniform conditions of soil and exposure, and deliberate search failed to turn up anything intermediate among the many individuals of the two easily distinguished sorts. Probably, however, these monocarpic daleas with small, short-lived flowers of drab coloring are autogamous and therefore breed true to form, behaving in effect as discrete species even when closely associated with another strain. Breeding experiments are required to determine the nature of these phenetically different strains, but it is doubtful whether their existence will ever deserve formal taxonomic status.
The nomenclature of D. humilis presents vexing problems, largely due to the loss or destruction of types. The holotypus of D. humilis itself is lost or at least not identified as such in the herbaria known to have inherited parts of Lambert’s herbarium (Miller, 1970). Don provided a clue to its identity by citing the manuscript binomial "D. herbacea Sesse", a name which turns up on two specimens dispersed by Pavon out of the Nueva Espana collection at Madrid. This seems, in conjunction with the short but convincing description, to fix application of the name, already suspected by Rydberg and accepted, without critical evaluation, by Clausen (Bull. Torrey Club 73: 83). A potential prior synonym exists in shape of Dalea acutifolia S. & M. ex DC. (1825), for three separate sheets of D. humilis (at G, OXF, P), ostensibly from the same source, were distributed under that name by Pavon. DeCandolle s description of D. acutifolia was compiled not from a specimen but from one of Sesse’s drawings, surviving as Caiques des Dessins PI. 228. This shows leaves suggestive of D. humilis, with the characteristic acute leaflets, but the massive spike is subsessile and terminal to an apparently erect stem and the foliage appears (and is described as) hairless. These last features, with the stylized but evocative figure of a detached flower, are more in accord with D. cliffortiana and cannot be reconciled with the Sesse specimens sent out as D. acutifolia by Pavon. For this reason I am listing D. acutifolia, which I used in annotation for D. humilis during the early years of this study, in the synonymy of D. cliffortiana.
The name D. ervoides was based, as noted already, on the slender extreme with few- flowered spikes and short bracts. The detailed protologue of D. inconspicua dispels all doubt as to the specific identity of the plant described, but suggests, contrary to Rydberg’s interpretation, a phase similar to D. ervoides. It appears, in fact, that no name is really available for the robust, thick-spiked aspect of D. humilis.
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Objects
Representative: MEXICO. Durango: Ripley & Barneby 13,500 (MEXU, NY), 13,957 (NY). Zacatecas: Pringle 1758 (BR, M, NY, UC, US, W). Nayarit: Ripley & Barneby 14,053 (NY). Jalisco: Palmer 573 (NY, UC, US); Ripley & Barneby 14,519 (CAS, NY); Rose & Painter 7616 (NY, US). Aguas Calientes: Gould 9007 (TEX, UC). Guanajuato: Ripley & Barneby 13,347 (CAS, MEXU, NY, US). Michoacan: Arsene 8426 (US); Ripley & Barneby 13,396 (MEXU, NY, US), 14,121 (CAS, NY). Mexico (incl. D. F.): Pringle 6233 (BR, ENCB, F, M, MEXU, NY, UC, US, W, Z), 8726 (ARIZ, F, L, M, NY, OKLA, UC, W, Z); Hinton 5030 (F, NY, W), 2617 (F, NY, MEXU). Hidalgo: Ripley & Barneby 13,628 (CAS, NY). Puebla: Arsene 1649 (NY, US); Purpus 4145 (F, NY, UC). Morelos: Pringle 11,292 (F, NY, Z); Berlandier 953 (OXF, P). Guerrero: Moore 5582 (BH). Oaxaca: C. L. Smith 546 (NY); Ripley & Barneby 13,643 (NY), 14,589 (CAS, NY). GUATEMALA. Huehuetenango: L. O. Williams et al. 22,108 (NY).
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Distribution
Mexico North America| Nayarit Mexico North America| Hidalgo Mexico North America| Durango Mexico North America| Michoacán Mexico North America| Puebla Mexico North America| Guerrero Mexico North America| Oaxaca Mexico North America| Guatemala Central America| Huehuetenango Guatemala Central America| Zacatecas Mexico North America| Jalisco Mexico North America| Guanajuato Mexico North America| Morelos Mexico North America|