Flora of North America species comparison

Crataegus uniflora is widespread in the southeastern United States from Long Island (New York) to eastern Texas; it is most abundant in the coastal plain and lower piedmont. A disjunction in the Mississippi embayment between trans-Mississippian and cis-Mississipian populations mirrors a similar pattern in C. spathulata (J. B. Phipps 1998).

Crataegus uniflora is usually easy to identify because of its small size, leaves small and coriaceous with lobes absent, numerous straight, fine thorns, inflorescences uniflorous or few-flowered, sepals glandular-pectinate and equal to or longer than the petals, anthers white to cream, and pomes yellowish to ruddy. Possible confusion with some members of ser. Lacrimatae is treated under the series discussion. Sterile plants might be confused with small, sterile ones of C. berberifolia (ser. Crus-galli) except for the smaller number of lateral veins on the leaves. An interesting feature of C. uniflora is the occasional deep lobing of extension-shoot leaves, even narrow ones, with veins to sinuses.

Crataegus uniflora is somewhat variable in plant size, leaf shape, number of flowers to an inflorescence (though commonly one), and anther color (usually ivory to cream). The typical form, which is common, has 1- or 2-flowered inflorescences, and is usually a small shrub with more or less spatulate to narrowly obovate leaves. Some particularly dwarf forms of this, on laterite soil in Georgia, have been observed with over 100 flowers when less than 3 dm.

Forms of Crataegus uniflora with 3–6-flowered inflorescences are also common and are represented by C. parvifolia and C. trianthophora. These are connected to the typical uniflorous kind by numerous intermediates and may be distinguished from the related C. brittonii by their smaller and narrower leaves with lobes absent.

Three anomalous variants, very similar or identical to Crataegus uniflora except for possessing small, more or less unlobed but glandular-serrate sepals, are known. These are: C. croomiana Sargent from northern Florida, C. bisulcata Ashe from North Carolina, and C. grossiserrata Ashe from Florida. The first, also best known, is further distinguished by pink anthers, the second by broader leaves, and the third by often orbiculate (unusual for ser. Parvifoliae) extension-shoot leaves with a tendency to deep lobing sometimes with veins to sinuses, and particularly strong and sharp leaf teeth. All suggest hybrid origin with ser. Lacrimatae.

(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.)