Dickinson Lab

"The Crataegus problem"

links to other labs working on the genus,
and to other useful or related sites
research questions

...and what about Mespilus?


In the beginning we have only a few unambiguous references to Crataegus.
In his White Goddess, Robert Graves identifies hawthorn as Uath, the May element of the tree calendar used in Europe in pre-christian times. Hawthorns are thus associated with the mother goddess in her various guises as maiden, nymph, and crone.
Theophrastus' History of Plants (transl. A. Hort 1916) contains vivid, accurate descriptions of plants, including both hawthorns and medlars. I haven't yet found out whether Crataegus or Mespilus appear in Dioscorides Materia medica, or in any medieval texts. However, since these genera appear in 17th and 18th c. herbals it seems likely that their use originated much earlier. Medlars (Mespilus) have been cultivated for centuries and so have a rich cultural heritage associated with them, as documented by Baird & Thieret (1989).
Beginning in early medieval times (and probably earlier) hawthorns were used to construct hedgerows along property boundaries in England. Because hedgerows provide safe sites for the establishment of other woody species their floristic richness has been used a means to date these hedgerows (Hooper 1971; Bradshaw 1971).

Linnaeus' Genera Plantarum (1737) revised many genera described by Tournefort (1700),
including both Mespilus and Crataegus.
Linnaeus' Species Plantarum (1753) named seven species still recognized as hawthorns, as well as the medlar.
Icosandria digynia include Crataegus coccinea, C. crus-galli, C. tomentosa, C. viridis, C. indica, C. laevigata (as C. oxyacantha), and C. azarolus, in addition to several other species now placed in other Maloid genera.
Oxyacantha  8. CRATAEGUS foliis obtusis bitrifidis serratis.

Crataegus laevigata - W. German stamp (1979)

The first four of these are all new world species, known to Linnaeus from the earlier works of Plukenet and Clayton, as well as from collections brought back to him by his student Kalm.

Icosandria pentagynia
include Mespilus germanica and several other species of Mespilus now placed in other Maloid genera.
germanica  1. MESPILUS inermis, foliis lanceolatis integerrimis suntus tomentosus, calycibus acuminatus.

Mespilus germanica - Albanian stamp 1965

Continued exploration of both Asia and North America led to descriptions of numerous new Crataegus species
During the late 18th and the 19th centuries many new species were described including ones collected by Lewis and Clark, David Douglas, Thomas Nuttall, and others as the western part of North America was explored more and more intensively.
Between 1896 and 1910 the number of North American Crataegus species increased dramatically.
Many of these species were described by C. S. Sargent, director of the Arnold Arboretum. Sargent eventually expressed himself to a correspondent about his pleasure in travelling in South America, where no hawthorns grew, but categorically denied that hybridization could be responsible for the large number of entities being discovered. The large number of species described during this period, together with the observations described below, led W. H. Camp (1942) to enunciate what he saw as "the Crataegus problem."
Reconsideration of species concepts in Crataegus
This quickly followed the discovery of polyploidy and other evidence (e.g. widespread male sterility) of hybridization in the genus (Standish 1916; Longley 1924). To date, however, hybridization has been studied in detail only in situations involving the Eurasian diploid species C. monogyna, not only in Europe (Raunkaier 1925; Bradshaw 1971; Byatt 1975; Christensen 1982, 1996) but also in North America where it has been introduced and hybridizes with native diploid species (Love & Feigen 1978; Wells & Phipps 1989). Polyploid Crataegus are apomictic and are suspected of being of hybrid origin, but only apomixis has been studied in any detail, and that only recently (Campbell et al. 1991). Even so, new species of Crataegus continue to be described without discussion of whether they merely represent apomictic genotypes, or in fact comprise populations of different, panmictic genotypes.
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links; people

Steve Brunsfeld
Knud Ib Christensen
Rhoda Love
Jim Phipps

links; websites

Rosaceae Evolution
Kew Record of Taxonomic Literature
Internet Directory for Botany
BOTANY Online- The Internet Hypertextbook
World Taxonomist Database
Medicinal uses of hawthorns
Morton Arboretum - Herbarium
Arnold Arboretum
Berkeley Botanical Garden
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What is an appropriate species concept for use in Crataegus?
Such a species concept must take into account the potential for hybrids and other variant genotypes to be perpetuated clonally by means of asexually-produced seed.

Phylogenetic systematics of Crataegus and Mespilus.
What are the phylogenetic relationships between the sections and series within Crataegus? Do these in fact represent clades within the genus? Do the two species of Mespilus form the sister-group of Crataegus?

What is the origin of the stamen number variation in the Crataegus?
What are the phylogenetic relationships between the North American 10- and 20-stamen forms? How did the derived stamen number arise? Why, with a single exception, are 10-stamen hawthorns not found in Eurasia?

Why are polyploid Crataegus restricted to triploids and tetraploids?
What mechanisms control the success of fertilization in crosses between ploidy levels? How frequently are unreduced gametes produced, and how often does uniparental reproduction occur?
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This page is a work in progress, jointly with students in my lab and others. Please use the mailto link below to send additional information that you would like to see here, e.g. a description of your own work on hawthorns and (or) medlars, useful links, recipes, or whatever you think might be useful and would be thought relevant.

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Please send your comments to tim.dickinson@utoronto.ca; last updated 15-Feb-03