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.)

Most specimens of Geum macrophyllum with glands on the pedicels also have the more deeply dissected leaves typical of var. perincisum; exceptions occur. Plants collected in the San Bernardino Mountains and the southern Sierra Nevada of California are so densely glandular as to fit this variety, yet their leaves are like those of var. macrophyllum. More troublesome are specimens from the Upper Peninsula of Michigan with sparsely glandular pedicels and leaves of var. macrophyllum. These plants are likely hybrids between the two varieties as their ranges overlap at the western end of the Great Lakes region. Occasional intermediate specimens were also seen from northern California to British Columbia where the ranges of the two varieties meet. Specimens of var. perincisum from around James Bay have deeply dissected leaves, but some have glandless pedicels and occasionally the styles are completely glabrous.

Variety perincisum hybridizes with Geum rivale (= G. ×pervale B. Boivin); see discussion under 8. G. rivale.

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