THE NORTH AMERICAN SUBDIVISIONS OF RANUNCULUS

NUMEROUS CHARACTERS enter into the delimitation of subgenera and sections of Ranunculus in North America north of Mexico. In the present paper the nectary-scale will be studied from the standpoint of its importance in this regard. The forms of the scale will first be described, after which keys, descriptions and a formal realignment of the subdivisions of the genus, based in part on the nectary-scale, will be presented. The presence of the scale covering the gland on the ventral side of the base of the petal-blade in Ranunculus has been known for many years. Linnaeus (1754) made the following statement: "Nectarium hoc in aliis porus nudus, in aliis margine cylindraceo cinctus, in aliis squammula emarginata clausus." This was translated by J. E. Smith (1819) as follows: "The nectary scale in Ranunculus, says Linnaeus, is, in some species, a naked pore; in some it is bordered with a cylindrical margin; in others closed with a notched scale." According to Smith, loc. cit., "The essential mark of the genus consists, as Linnaeus remarks, in the nectary, the rest of the parts being uncertain; hence he takes occasion to point out the use of adverting to that organ, which before his time had been neglected, and which his opponents accuse him of sometimes making of too much importance...." Apparently no one since Linnaeus has checked the variability of the nectary-scale in the various subgenera, sections, and species of Ranunculus, and the literature of the subject is meager. It consists of a few fragments, as follows: The supposed absence of the scale in Batrachium is treated in standard manuals, such as Gray's Manual and Jepson's Manual of the Flowering Plants of California, as a distinguishing feature of the subgenus. Drew (1936) made the following statement concerning Batrachium: "The nectarial scales at the base of the petals are, according to Freyn (1881), consistently round; but my studies show that the nectaries vary considerably in their development within a given species. Indeed the simple round type is scarcely present in most petals of our North American Species." Parkin (1928) pointed out the fact that the nectary-scale of Ranunculus flabellaris (R. delphinifolius) differs radically from the simple scales occurring in such species as Ranunculus acris, R. repens, and R. californicus, which often are studied in elementary taxonomy. The present study of Ranunculus has revealed six tvpes of nectary-scale, as follows: (1) a transverse ridge basal to the gland (fig. 12); (2) a simple flap (fig. 1); (3) a pocket (fig. 2-9, 11); (4) a forked structure produced distally and sometimes finally free from the petal at the tips of the two branches (fig. 13, 16, 17); (5) a circular or obovate border (fig. 14, 15); (6) differentiation of a primary scale, which bears the gland on its ventral surface, 1 Received for publication June 29, 1940. and of a secondary scale, which forms a pocket enclosing the gland (fig. 10). Scales of any of the six types may be proximally truncate (fig. 1, 8, 1 1, 12 ), rounded (fig. 13, 15), or angular (fig. 2-7, 16, 17) and distally truncate (fig. 2, 4, 6-8), emarginate (fig. 1, 3), 3-lobed (fig. 3), curved outward (fig. 9), or curved inward (fig. 5, 11). Commonly the scale is glabrous, but in some species the distal margin is ciliate (fig. 6-9), and sometimes the neighboring surface of the petal also produces hairs (fig. 9). In some species the nectary-scale is variable (fig. 3, 4), but in most it is not variable in form, and in nearly all it is of a constant basic type. Moreover, particular basic types almost consistently characterize the subgenera and sections of the genus, as previously delimited for the species occurring in the Pacific States (cf. Benson, 1936) primarily on the basis of other characters. The relationship of the six types of nectary-scale to the classification of the North American subgenera and sections of Ranunculus is indicated in the following list: