BOT 360F - Families of Vascular Plants

ROSACEAE: Maloideae
Crataegus spp.

Crataegus (hawthorn) and the closely related genus Mespilus (medlar) pose challenging problems for taxonomists and evolutionary biologists because of the occurrence of hybridization, polyploidy, and apomixis. Here they will also serve to exemplify similar problems also encountered in other Maloideae such as Amelanchier, Cotoneaster, and Sorbus, among others. Hawthorns colonize sites with high light levels and exposed soil (erosion surfaces, abandoned agricultural land) and resist grazing by vertebrates because of their thorns. They can reproduce prolifically, and in all respects can be thought of as long-lived, woody weeds. Click HERE to visit a page that discusses the interrelationships between these issues as they relate to hawthorn taxonomy.

Crataegus tenax in flower Like most Maloideae, Crataegus has unspecialized pentamerous flowers with a hypanthial ovary. Virtually all Eurasian Crataegus species, regardless of ploidy level, and all known North American diploids have 20 stamens per flower. Style and locule number varies from one to five, but some individuals may produce some flowers lacking gynoecia altogether. Within each locule the two ovules are superposed, so that only the micropyle of the lower one is associated with the funicular obturator. North American hawthorns are unusual in that stamen numbers also vary, with modes of 5, 10, 15, and 20 depending on species. Variation in stamen number may represent selection for optimal pollen dispersal (click HERE to read a paper on this topic). Lower numbers of stamens apparently result from the loss, rather than suppression, of stamen whorls (Evans & Dickinson 1996).
Crataegus punctata var. aurea in fruit

Hawthorns reproduce not only sexually but also asexually, by means of gametophytic apomixis (vegetative reproduction from root sprouts also occurs in some species).


haw flakes

The polypyrenous drupes of Crataegus can be an important food source for wildlife, including grouse, pheasant, pine grosbeak, fox sparrow, gray fox, pine mouse, and white-tailed deer. Hawthorn fruits are used for food by humans as well (e.g. tejocote, C. pubescens, in Mexico and Guatemala; C. azarolus, in southern Europe and Asia Minor; C. pinnatifida, in China). Hawthorn fruits are also used in herbal remedies for circulatory system problems because of their flavonoid content.

Photo: R. Presgrave, © 2000, Royal Ontario Museum.

Crataegus tenax pyrenes Open-pollinated fruits typically contain only a single filled seed, regardless of pyrene number. Seeds require cold stratification to germinate.
Mespilus germanica fruit Click HERE to link to a page describing current studies of Crataegus and Mespilus evolution and systematics. Click HERE to link to a brief report on recent studies of nuclear DNA sequence variation in Crataegus and Mespilus.
medlar jelly
Medlars (Mespilus germanica) are almost indistinguishable from hawthorns and are known outside of cultivation only in Asia Minor and western Asia. Recently, a second species, M. canescens, was described based on material from a single population in Arkansas (Phipps 1990).

Selected references

Baird, J. R. & Thieret, J. W. (1989). The Medlar (Mespilus germanica, Rosaceae) from antiquity to obscurity. Economic Botany 43: 328-372.

Bradshaw, A. D. (1971). The significance of hawthorns. Hedges and local history. London, National Council of Social Service: 20-29.

Brinkman, K. A. (1974). Crataegus L. Seeds of woody plants in the United States. Washington DC, United States Forest Service, United States Department of Agriculture. 450: 356-360.

Brown, H. B. (1910). The genus Crataegus with some theories of the origin of its species. Bulletin of the Torrey Botanical Club 37: 251-260.

Byatt, J. I. (1975). Hybridization between Crataegus monogyna Jacq. and C. laevigata (Poiret) DC. in southeastern England. Watsonia 10: 253-264.

Byatt, J. I. (1976). Pollen morphology of some European species of Crataegus L., and of Mespilus L. (Rosaceae). Pollen et Spores 18: 335-349.

Camp, W. H. (1942). The Crataegus problem. Castanea 7: 51-55.

Campbell, C. S., Greene, C. W. & Dickinson, T. A. (1991). Reproductive biology in subfamily Maloideae (Rosaceae). Systematic Botany 16: 333-349.

Christensen, K. I. (1982). A biometric study of some hybridizing Crataegus populations in Denmark. Nordic Journal of Botany 2: 537-548.

Christensen, K. I. (1992). Revision of Crataegus Sect. Crataegus and Nothosect. Crataeguineae (Rosaceae-Maloideae) in the Old World. Systematic Botany Monographs 35: 1-199.

Courtney, S. P. & Manzur, M. I. (1985). Fruiting and fitness in Crataegus monogyna: The effects of frugivores and seed predators. Oikos 44: 398-406.

Dickinson, T. A. (1985). The biology of Canadian weeds. 68. Crataegus crus galli sensu lato. Canadian Journal of Plant Science 65: 641-654.

Dickinson, T. A. (1999). Species concepts in agamic complexes. Plant evolution in man-made habitats. Raamsdonk, L. W. D. v. & Nijs, J. C. M. d. (eds.). Amsterdam, Hugo de Vries Laboratory, Institute for Systematics & Ecology, University of Amsterdam: 319-339.

Dickinson, T. A. & Campbell, C. S. (1991). Population structure and reproductive ecology in the Maloideae (Rosaceae). Systematic Botany 16: 350-362.

Dickinson, T. A. & Love, R. M. (1997). [North American black-fruited hawthorns: III.] What IS Douglas hawthorn? Conservation and Management of Oregon's Native Flora. Kaye, T. (eds.). Corvallis OR, Native Plant Society of Oregon.

Dickinson, T. A. & Phipps, J. B. (1984). Studies in Crataegus L. (Rosaceae: Maloideae) IX. Short shoot leaf heteroblasty in Crataegus crus-galli L. sensu lato. Canadian Journal of Botany 62: 1775-1780.

Dickinson, T. A. & Phipps, J. B. (1985). Studies in Crataegus L. (Rosaceae: Maloideae) XIII. Degree and pattern of variation in Crataegus section Crus-galli in Ontario. Systematic Botany 10: 322-337.

Dickinson, T. A. & Phipps, J. B. (1986). Studies in Crataegus (Rosaceae: Maloideae) XIV. The breeding system of Crataegus crus galli sensu lato in Ontario (Canada). American Journal Of Botany 73: 116-130.

Eggleston, W. W. (1908). The Crataegi of the northeastern United States and adjacent Canada. Rhodora 10: 73-84.

Evans, R. C. & Dickinson, T. A. (1996). North American black-fruited hawthorns (Crataegus section Douglasii Loud.): II. Floral development of 10- and 20-stamen morphotypes. American Journal of Botany 83: 961-978.

Guitian, J. & Fuentes, M. (1992). Reproductive ecology of Crataegus monogyna in northwestern Spain. Acta Oecologia 13: 3-11.

Guo, T. & Jiao, P. (1995). Hawthorn (Crataegus) resources in China. HortScience 30: 1132-1134.

Hebda, R. J., Chinappa, C. C. & Smith, B. M. (1988). Pollen morphology of the Rosaceae of western Canada. I. Agrimonia to Crataegus. Grana 27: 95-113.

Kruschke, E. P. (1965). Contributions to the taxonomy of Crataegus. Milwaukee WI, Milwaukee Public Museum.

Muniyamma, M. & Phipps, J. B. (1979a). [Studies in Crataegus (Rosaceae: Maloideae). I.] Cytological proof of apomixis in Crataegus (Rosaceae). American Journal of Botany 66: 149-155.

Muniyamma, M. & Phipps, J. B. (1979b). [Studies in Crataegus (Rosaceae: Maloideae). II.] Meiosis and polyploidy in Ontario species of Crataegus in relation to their systematics. Canadian Journal of Genetics and Cytology 21: 231-241.

Muniyamma, M. & Phipps, J. B. (1984). Studies in Crataegus. X. A note on the occurrence of diplospory in Crataegus dissona Sarg. (Maloideae, Rosaceae). Canadian Journal of Genetics and Cytology 26: 249-252.

Muniyamma, M. & Phipps, J. B. (1985). Studies in Crataegus. XII. Cytological evidence for sexuality in some diploid and tetraploid species of North American hawthorns. Canadian Journal of Botany 63: 1319-1324.

Phipps, J. B. (1988). Crataegus (Maloideae, Rosaceae) of the southeastern USA: I. Introduction and series Aestivales. Journal of the Arnold Arboretum Harvard University 69: 401-432.

Phipps, J. B. (1991). Mespilus canescens, a new Rosaceous endemic from Arkansas. Systematic Botany 15: 26-32.

Phipps, J. B. & Muniyamma, M. (1980). [Studies in Crataegus (Rosaceae: Maloideae) III.] A taxonomic revision of Crataegus (Rosaceae) in Ontario. Canadian Journal of Botany 58: 1621-1699.

Phipps, J. B., Weeden, N. F. & Dickson, E. E. (1991). Isozyme evidence for the naturalness of Mespilus L. (Rosaceae, subfam. Maloideae). Systematic Botany 16: 546-552.

Ptak, K. (1986). Cyto-embryological investigations on the Polish representatives of the genus Crataegus L. I. Chromosome numbers; embryology of diploid and tetraploid species. Acta Biologica Cracoviensia Series: Botanica 28: 107-122.

Ptak, K. (1989). Cyto-embryological investigations on the Polish representatives of the genus Crataegus L. II. Embryology of triploid species. Acta Biologica Cracoviensia Series: Botanica 31: 97-112, Pl. 5.

Rickett, H. W. (1936). Forms of Crataegus pruinosa. Botanical Gazette (Crawfordsville) 97: 780-793.

Rickett, H. W. (1937). Forms of Crataegus crus-galli. Botanical Gazette (Crawfordsville) 98: 609-616.

Wells, T. C. & Phipps, J. B. (1989). Studies in Crataegus (Rosaceae: Maloideae). XX. Interserial hybridization between Crataegus monogyna (series Oxyacanthae) and Crataegus punctata (series Punctatae) in southern Ontario. Canadian Journal of Botany 67: 2465-2472.

Williams, P. A. & Buxton, R. P. (1986). Hawthorn (Crataegus monogyna) populations in mid-Canterbury. New Zealand Journal of Ecology 9: 11-17.

Zohary, D. & Hopf, M. (1988). Domestication of plants in the old world. Oxford, Clarendon Press.

All photos © 2000, T. A. Dickinson except as noted.

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