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Crataegus: hawthorns or thornapples
Crataegus
is a large genus of trees and shrubs with fruits similar in appearance
to small apples (Malus pumila), and in most cases with
conspicuous thorns on the branches. The taxonomy of Crataegus
remains unsettled. It appears that various aspects of reproduction
in this genus have resulted in numerous distinctive local populations
difficult to relate to others, and botanists have probably recognized
more species than actually exist. There does not appear to be
a workable method of identifying the species based on vegetative
characters. Indeed, all credible keys for our area require that
individuals be tagged and revisited so that flowers, fruit and
mature leaves can be collected before identification is possible.
The list below includes all (17) species of Crataegus judged
to be of tree form in Wisconsin. Fourteen of these species generally
have at least shallow lobes in addition to teeth on the leaf margins.
C. crus-galli and C. punctata, (and sometimes C.
succulenta) are toothed, but usually unlobed. An additional
23 species of Crataegus reported for Wisconsin are deemed
to be shrubs and are not listed here.
Few, if any, current botanists in Wisconsin claim
thorough knowledge of Crataegus, and I offer no new insights
to the means of recognizing species here. In my experience, the
number of individual plants of Crataegus is far greater
in the southern half of the state, north to Brown County. In Brown
County Crataegus is widespread and numerous, especially
in disturbed, sunny locations, including consistently grazed areas
where the competing plants are apparently diminished by the cattle,
and Crataegus and its thorns are left to prosper. The most
common species in Brown County appears to be C. mollis
and it is apparently the first species to flower in this area
each spring. C. punctata is also common and C. crus-galli
is widely planted. North of Green Bay, in northeastern Wisconsin
C. chrysocarpa appears well distributed, though not usually
numerous. Several other species are currently under observation,
but I can offer no further insight into the Crataegus of
Wisconsin based on my own observations.
The following list includes all 17 tree species
of Crataegus reliably reported for Wisconsin.
Based on distribution maps from the University
of Wisconsin-Madison, derived from confirmed specimens from several
Wisconsin herbaria, relatively common tree species of Crataegus
include C. calpodendron (southern WI), C. chrysocarpa
(throughout WI, but more records from the south) , C. holmesiana
(SE WI), C. mollis (common in SE), C. pedicellata
(mostly SE), C. pruinosa (mostly southern 3 tiers of counties),
C. punctata (southern ¾), C. schuettei (eastern)
and C. succulenta (mostly southern, but a few north).
For those brave enough to pursue further identification
of Crataegus specimens in Wisconsin, the following works
will prove valuable.
Kruschke, Emil P. 1965. Contributions to the Taxonomy
of Crataegus. Milwaukee Public Mus. Publ. Bot. 3. 273 pp.
Voss, E.G. 1985. Michigan Flora. Part II. Dicots (Saururaceae-Cornaceae).
Cranbrook Inst. of Sci. Bull. 59 & Univ. Mich. Herb. 724 pp.
Crataegus covers pages 386-418.
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