Dalea candida
Rupert C. Barneby
41. Dalea candida Michaux ex Willdenow
(Plate LVI)
Herbaceous from an ultimately thick, tough taproot and knotty root-crown or short caudex situated at or just below soil-level, variable in stature (3-10 dm) and in habit of growth, the erect or diffuse, pale green or stramineous, prominently ribbed, glandless or minutely punctate stems simple or branched from near middle or only distally, the foliage either rich green or pallid-glaucescent, the leaflets smooth above, punctate beneath; leaf-spurs 0.2-1 mm long; stipules triangular-subulate to narrowly lanceolate, greenish becoming stramineous or brownish, sometimes minutely livid- glandular, (1) 1.5-5.5 mm long; intrapetiolular glands 0 or impressed and minute; post-petiolular glands either prominent or immersed; leaves subsessile or short- petioled, the main cauline ones (sometimes drought-deciduous) 1.5-6 cm long, with broadly margined, usually punctate rachis and 2-4 pairs of leaflets variable in size and outline, obovate to elliptic-oblanceolate or linear-oblong, either acute, short-acuminate, or emarginate, flat or loosely folded, up to 0.7-3.5 cm long, the terminal one either sessile or short-stalked, longer than the rest; peduncles in reality very short or 0, but leaves at 2-several nodes preceding the spike almost always reduced to stipuliform bracts, the stem hence leafless for 1-14 (20) cm distally and simulating a peduncle; spikes variable in density, cone- or ament-like, ovoid to cylindroid (a few sometimes subglobose), without petals 6-10 mm diam, the glabrous or minutely pilosulous axis 1-5.5 (7.5) cm long; bracts subdimorphic, the lowest firm, reflexed, persistent, the rest deciduous by anthesis (sometimes held fast between the calyces), greenish or livid-castaneous beyond the papery base, the body narrowly obovate to oblanceolate, contracted into a tail as or only half as long, all usually narrowly pallid- margined, minutely ciliolate, gland-sprinkled dorsally; bracteolar spicules (0.5) 0.6 1.6 mm long, minutely ciliolate; calyx (2.9) 3-4.2 (4.4) mm long, glabrous except for minutely ciliolate inner margin or inner face of teeth or, less commonly, the tube externally pilosulous with fine weak hairs less than 0.4 mm long, the subsymmetric tube 1.9-2.7 mm long, angular-pleated, not recessed behind banner, the prominent but slender ribs often castaneous, the firmly membranous intervals either pallid or castaneous-flecked, charged (nearly always) near the orifice with 1, less often 2-3, usually small transparent or yellow blister-glands, the firm, green or livid, ± connivent teeth somewhat unequal, the dorsal one longest and narrowest, lanceolate or narrowly triangular, 1-1.8 mm long, usually 0.6-1.4 mm shorter than tube, the ventral pair a little shorter, triangular to deltate; petals white, glandless; banner (4) 4.2-5.7 mm long, the filiform claw (1.9) 2.2-3.8 mm, the broadly deltate-obovate, obtuse or emarginate, hooded blade deeply cordate at base, 2.3-3.4 mm long, 2.4-3.7 (4.2) mm wide; epistemonous petals subhomomorphic, 3.2-5.2 mm long, the filiform claw (0.7) 0.9-2.3 mm, the oblong, oblong-oblanceolate, or elliptic-oval blade concave at the obtuse or subemarginate apex, 2-3.5 mm long, 1.3-2.1 mm wide; androecium (5) 5.2-7.6 mm long, the column 2.3-3.5 mm, the free filaments up to 2.5-4.5 mm long, the connective gland-tipped, anthers yellow, (0.7) 0.8-1.3 mm long; pod very obliquely half-obovate or obliquely clavate in profile, ordinarily exserted, (2.6) 2.84 (4.5) mm long, the ventral suture straight or slightly concave, the style-base excen- trically terminal, the convex prow thickened and prominent, the valves hyaline at base, firm and sometimes thinly pilosulous distally, charged near or above middle with a crescent of usually contiguous and oblong, sometimes round and more scattered, pale or orange blister-glands; seed oblong-elliptic, ± 1.7-2.3 mm long.
The prototype of the white prairie-clovers and generitype of Petalostemum, a complex species of wide dispersal, closely related only to D. multiflora, which has essentially the same flower-structure but (at least ideally) more numerous, shorter flower-spikes combined with slightly more numerous leaflets. Despite evidence persuasively deployed by Isely & Welsh (1960), quoted and amplified by Wemple (1970, p. 46-7), I persist here in a comprehensive concept of D. Candida wide enough to embrace the diverse forms referred by these authors to Petalostemon occidentale. My dissent is founded on no new data, but on reinterpretation of facts long known.
Summing up the case for recognition of P. occidentale at specific level, Wemple appeals to the use of "multiple" differential characters, reduced in the key to two: an elongating spike and a more prominently ribbed, usually pilosulous calyx. It later emerges, however, that the calyx may be glabrous, but then accompanied by fewer, ordinarily (but not reliably) smaller leaflets and a more diffuse habit of growth. The prominence of the calyx- ribs appear to me as a function of spike-density. When the calyces, as in genuine P. candidum, are closely compacted, their tubes assume from mutual pressure, not exerted in the case of the loosely spicate P occidentale, a more bluntly pentagonal figure. If this is so, the multiple differences are reduced to one. In the middle prairie region P. candidum extends west into the treeless prairie zone only in the rich bottomlands along rivers, where it finds conditions similar to those encountered east of the Mississippi. In the same longitudes P. occidentale extends eastward from its centers of abundance only in xeric habitats such as river-bluffs and eroded badlands. The populations within this band of sympatry appear to behave as ecologically allopatric species, but remain morphologically distinct only if an assessment of the whole variation within each species is ignored. The vexing populations of P. occidentale from the northwestern prairies which resemble P. candidum either in glabrous calyces, or large leaflets, or both at once, are interpreted by Wemple as independent variations with no direct genetic contact with genuine P. candidum, and therefore somehow irrelevant to the taxonomic problem. Yet these very plants, which mimic P. candidum except for their looser flower-spike, or shorter stem, or both, obstinately suggest that there survives in the genetic resources of P. occidentale a rich potential in common with its eastern counterpart. No analysis, however sophisticated, can eliminate them from the record.
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:
