Flora of North America species comparison

Varieties 6 (6 in the flora).

Crataegus pruinosa extends from Arkansas to Wisconsin, through the southern Great Lakes to southern New England, and, in the south, mainly in the Appalachians to northern Georgia.

In the north of its range, Crataegus pruinosa is mainly a shrub of open successional habitats but in the south may commonly be a taller tree of open or thin woodlands.

Many hawthorns have a little waxy bloom on their pomes; it is particularly prominent on Crataegus pruinosa and C. cognata compared to others. Some authors include in C. pruinosa their white-anthered counterparts, here assigned to C. cognata. Whereas C. pruinosa characteristically has entire or subentire sepal margins, some forms in the southwest of the range of the species (for example, C. calliantha Sargent, C. seducta Sargent) may have glandular-serrate sepal margins. They may represent introgression with C. coccinioides. The varieties of C. pruinosa are weakly differentiated from each other, most of them on leaf shape and size characters. The more widespread varieties constitute a range of morphotypes held together by common traits. Crataegus gaudens Sargent is a strikingly distinct form from Pennsylvania that has more or less elliptic leaves with lobes absent; it is clearly related to C. pruinosa. Note that 159. Crataegus ×coleae, a Michigan endemic, will key out here if its laterally scarred pyrenes are missed.

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

Crataegus rivulopugnensis, known only from the Cypress Hills, is widely distributed in the western part. The species is most similar to C. purpurella, though the color of the ripe fruit in the two species is quite different (red versus deep purple). They differ also in an almost allopatric distribution, habit when open-grown, and leaf size and numbers of veins per side (4 or 5 versus 3 or 4). Both species have less hairy adaxial leaf surfaces than most other sympatric hawthorns, often being glabrate adaxially at maturity.

INTERSERIAL HYBRIDS AND SPECIES OF HYBRID ORIGIN

Numerous putative interserial hybrids among North American hawthorns have been given binomials (J. B. Phipps 2005). Nearly all the named putative hybrids have proven to be rare or even apparently extinct. All of the 16 treated here satisfy at least two of the following criteria: there is a high degree of confidence that they are of interserial hybrid origin; they do not fit into any accepted series; they continue to be found long after their initial description, indicating either apomictic perpetuation, repeated creation, or both; or, they have appeared regularly as species in the literature, notably in works by E. J. Palmer. It is notable that most remain uncommon, suggesting that these are not particularly fit biotypes. Nevertheless, persisting populations of some (for example, Crataegus persimilis) may be readily found. The fifteenth example (C. turnerorum) is a well-collected, obviously persistent, local species in Texas.

The putative interserial hybrid, Crataegus florifera, however, is treated in the main text (in this case under ser. Anomalae) because it fits the serial description adequately and has significant and continuous ranges. Other examples included in the main text are some putative ser. Punctatae × ser. Crus-galli crosses that will be found associated with C. collina. The best studied interserial hybrids are two without names (though this will change with a forthcoming paper by the Dickinson group), both hybrids of the introduced C. monogyna. Here they are treated in the main text with their native parental species (C. punctata and C. suksdorfii). Neither of these hybrids is considered especially rare, and both appear to be increasing in frequency but so far there is no evidence of a fixed hybrid establishing.

Hybrids among North American native species have probably arisen multiple times (J. B. Phipps 2005); however, there was little evidence for the creation of successful new biotypes until some recent papers by the Dickinson group demonstrating modern derivatives of ancient alloploid of ser. Crataegus (E. Y. Y. Lo et al. 2009) and perhaps more recent alloploid derivatives from ser. Douglasianae (T. A. Dickinson, pers. comm.). Hybridization among more closely related apomicts may be more frequent than previously thought (Dickinson et al. 2008) but, with more cryptic characteristics, may more easily escape detection.

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