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.)

Geum virginianum has been confused nomenclaturally with G. laciniatum. B. L. Robinson and M. L. Fernald (1908) and J. K. Small (1933) misapplied the name G. virginianum to the species correctly named G. laciniatum, and they used the names G. flavum (Robinson and Fernald) and G. hirsutum (Small) for what is correctly named G. virginianum. Much of what is named G. virginianum in older herbarium collections is actually G. laciniatum.

In habit and leaf form, Geum virginianum is similar to G. canadense. Geum virginianum differs in having cream petals shorter than the sepals (versus white and usually equal to or longer), the largest stipules of the cauline leaves 20–48 × 10–35 mm (versus smaller), and the stems hirsute to densely hirsute (versus glabrate to downy with only scattered longer hairs). The variability within G. canadense is so great that for some specimens it is difficult to determine whether they belong to G. canadense or G. virginianum.

L. A. Raynor (1952) believed Geum virginianum to be an F1 hybrid between G. aleppicum and G. canadense. K. R. Robertson (1974) acknowledged that some herbarium specimens assignable to G. virginianum from the area where G. aleppicum and G. canadense are sympatric have mostly aborted pollen and may represent natural hybrids. He pointed out that farther south, where G. aleppicum is absent, specimens of G. virginianum appear fully fertile and seem to represent a valid species.

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