Flora of North America species comparison

Varieties 2 (2 in the flora).

Characters useful in recognizing specimens of Geum macrophyllum are yellow petals, epicalyx bractlets often absent, proximal style segment sparsely to densely stipitate-glandular, and fruiting receptacles puberulent. Across its broad North American range from Alaska to California and Nova Scotia, G. macrophyllum exhibits considerable variation. Based largely on the shape of the terminal leaflet of the basal leaves and the degree of dissection and shape of the divisions of the distal cauline leaves, P. A. Rydberg (1913b) distinguished three species within the range of variation treated here as one species. Basal leaves of G. macrophyllum in the strict sense (var. macrophyllum in this treatment) have relatively large reniform to rounded terminal leaflets and the distal cauline leaves are three-cleft into rhombic or cuneate lobes. The basal-leaf terminal leaflets of G. perincisum (= var. perincisum) are only slightly larger than the laterals and are deeply lobed into rhombic-obovate segments; the distal cauline leaves are dissected into oblanceolate divisions. Both basal and cauline leaves of G. oregonense (= var. perincisum) are intermediate between those of G. macrophyllum and G. perincisum. W. Gajewski (1955) crossed all three taxa under discussion and examined leaf morphology and cytology of the F1 and F2 hybrids. He concluded that they were distinct but not yet completely separated species. Fairly well correlated with the more dissected leaves of G. oregonense and G. perincisum is the presence of minute stalked glands on the pedicels. The treatment here follows H. M. Raup (1931) in recognizing two varieties of G. macrophyllum based more on pedicel glandularity than leaf morphology.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Specimens from Chicago, Illinois, and Cambridge, Massachusetts, indicate that Geum urbanum has been present in North America for at least 100 years; herbarium specimens are scarce. The species seems to be spreading in ruderal habitats of the northeastern United States and adjacent Canada. The plants have the habit and foliage of G. canadense and G. virginianum, with stipules as large as or even larger than those of the latter; the petals are bright yellow versus white or cream, and the distal segments of the styles are glabrous or nearly so versus partially pilose.

Geum urbanum is often found growing near G. canadense, and the two occasionally form hybrids; G. ×catlingii J.-P. Bernard & R. Gauthier is known from New Brunswick, Ontario, Quebec, and Michigan. Less common is G. ×macneillii J.-P. Bernard & R. Gauthier [G. laciniatum × G. urbanum], known from Quebec. Both hybrids closely resemble G. urbanum in vegetative form, with little hint of their other parent; it is likely that hybrid plants often go undetected. Most herbarium specimens of these hybrids were collected along with their parental species at the same locality. The hybrids are often robust, apparently showing hybrid vigor. Unlike G. urbanum, they have cream petals and heads with mostly sterile ovaries.

(Discussion copyrighted by Flora of North America; reprinted with permission.)