Flora of North America species comparison

Varieties 2 (2 in the flora).

At the beginning of the twentieth century, E. L. Greene described over a dozen species belonging to the Geum triflorum complex based on differences in leaf form and indument, the relative length and shape of the epicalyx bractlets and sepals, and petal length and shape. Most of these species were quickly reduced to synonymy by other botanists. When specimens are examined from across the continent, most of the characters used to separate species in the G. triflorum complex show nearly continuous variation. It seems best to treat these variants as belonging to one species. Whether and how to classify the variation within the species will remain controversial. Some character expressions correlate reasonably well with dividing the species into two varieties, as was first proposed by N. C. Fassett (1928). Variety triflorum occurs east of the Rocky Mountains and is typical of the grasslands covering the northern Great Plains; it also is the variety found in the mountains of Arizona and New Mexico. Variety ciliatum is common throughout the rest of the Rocky Mountains, the Sierra Nevada, and Cascade Range. Intermediate specimens occur here and there, particularly in Alberta and British Columbia.

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

Of conservation concern.

Geum schofieldii is one of the more attractive yet seldom seen species of avens in North America; it is known from the rocky wet mountains of the Queen Charlotte Islands and northern Vancouver Island.

Because Geum schofieldii appears to be intermediate morphologically between G. calthifolium and G. rossii, some botanists have considered it to be a hybrid and included it in synonymy with G. ×macranthum [G. calthifolium × G. rossii]. The 16-ploid chromosome number (2n = 112) of G. schofieldii suggests an allopolyploid origin. Geum rossii is not known to occur in the Queen Charlotte Islands or on Vancouver Island; the plants cannot be of recent hybrid origin. Geum ×macranthum is found in the Aleutian Islands and the Alaska Peninsula where the two parental species overlap. Compared to G. schofieldii, its leaves are more pinnate than lyrate-pinnate, with 9 to 13 major leaflets instead of 5 to 7. Also, G. ×macranthum appears to be sterile; G. schofieldii appears to be fertile, suggesting that the latter is a valid species. The distinctness of G. schofieldii pollen also supports its specific status (R. J. Hebda and C. C. Chinnappa 1990).

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