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 persimilis has a large but sporadic distribution; some populations appear to be self-perpetuating. The species is widely cultivated.

Crataegus persimilis is plausibly a hybrid complex of C. crus-galli in the broad sense with C. succulenta in the broad sense. This is suggested by the glossy and subcoriaceous leaves like C. crus-galli, with larger size and broader proportions as in C. succulenta, and also dark and glossy one-year-old twigs, very dark, more or less stout one-year-old thorns, deeply incised sepal margins, and commonly pitted pyrenes (the sides usually excavated with a slit).

Included here is a substantial range of forms among which there is considerable variation in leaf shape, inflorescence indumentum, stamen number, anther color, pyrene excavation as well as other characters. The type form from near Rochester, New York, has the narrowest leaves (length/width = 1.5–2), most stamens (10–20), pink anthers, sparsely pubescent inflorescence branches, and deeply pitted pyrenes. The commonly cultivated ‘prunifolia’ form is similar but has a much broader leaf (length/width = 1.3–1.5) as well as densely pubescent or nearly tomentose inflorescence branches, and ten pink anthers. Crataegus helderbergensis resembles the last but has 10–14 white anthers and no lateral excavation to the pyrenes. Other similar taxa that are candidates for inclusion are: C. robusta, with wide leaves and nearly glabrous inflorescence branches, larger flowers (18 mm diam.), 10–20 pink anthers, plane-sided pyrenes in the type though excavated in syntype material; C. cerasina, similar, with laterally pitted pyrenes and smaller flowers (12 mm diam.). Crataegus livoniana Sargent has leaves more like C. crus-galli but barely eroded pyrenes and may not belong. Crataegus laetifica of Pennsylvania and Ohio is another similar form.

The cultivated plant is often called Crataegus prunifolia Persoon in the horticultural literature; this name is invalid because it is a later homonym of C. prunifolia (Marshall) Baumgarten, a synonym of Aronia prunifolia, the chokeberry. Crataegus persimilis, in its 'prunifolia' form is one of the more popular cultivated hawthorns. It is a handsome ornamental when well grown, with glossy foliage, striking scarlet fruit and fall color of foliage.

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