Flora of North America species comparison

Crataegus douglasii occurs from southern and western British Columbia to the panhandle of Alaska and ranges to northern California and the Rocky Mountains of Idaho, Montana, and southwestern Alberta. Disjunct populations occur farther east in the Cypress Hills (Alberta and Saskatchewan), the Montana montane islands, and around the northern Great Lakes. In western North America, C. douglasii is found mainly near water in drier areas; in more mesic regions, it may occur in open woodlands. In the Great Lakes area, it mainly occurs in old pastures and on fencerows.

Crataegus douglasii is distinguished from C. gaylussacia by having ten stamens and is rather variable in leaf shape and size. The species is distinguished from C. okennonii by the latter usually being taller and typically more erect as well as having a usually straight, single trunk, shorter thorns, ampulliform-orbicular fruit, and often purplish crimson fall foliage. Crataegus castlegarensis is the most similar species, and beyond possessing relatively few to many multiple thorns, it is distinguished from C. douglasii by its hairy hypanthia, pedicels, and, often, fruit, which is orbicular, plump, crimson to purple in late August, ripening to deep purple (sometimes black) at a time when sympatric C. douglasii is fully black.

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

Crataegus macracantha is the most widespread North American hawthorn and one of the more variable. Variation is particularly great in Quebec and Montana. Attempts to package the variation into named taxa have hitherto run into the problems that the type is an illustration of inadequate quality and that authors have been insufficiently aware of the total variation. Two common eastern forms are similar white-anthered and pink-anthered with abaxially glabrous, broadly elliptic-ovate leaves, shallowly and sharply lobed, and fruit ripening directly from green to red; these have the longest thorns in the species, and both have been treated as if typical.

Crataegus occidentalis, a white-anthered, intermontane form with leaves similar to the foregoing usually has shorter thorns and fruit ripening to red through a characteristic orange or salmon stage. Pink-anthered C. pertomentosa, with leaves of a similar shape but abaxially pubescent to tomentose grows on the Great Plains. The last two forms have been treated as varieties. Other striking variants have brilliant red bracteoles or strongly convex leaves (both from Montana) and entire-margined sepals (C. integriloba Sargent from Quebec). Some rare forms have glabrous inflorescences. Some populations in northwestern Montana, otherwise much like a common pink-anthered sympatric form, have glandular petioles and may represent introgression from another species.

Crataegus macracantha often forms suckering thickets in the east.

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