Genus: Crataegus

Crataegus crus-galli
Crataegus crus-galli

By Science Staff

Not peer reviewed

Last Modified 01/18/2012

Back to Rosaceae


Crataegus L., Sp. Pl. 475. 1753. Gen. Pl., ed. 5, 213. 1754. Oxyacantha Medik., Philos. Bot. 1: 150, 154, 155. 1789, nom. illeg. (Art. 52.1). LECTOTYPE: Crataegus oxyacantha L., designated by Britton & Brown (1913).

Xeromalon Raf., New Fl. 3: 11. 1838. TYPE: Xeromalon obovatum Raf.

Phaenopyrum M. Roem., Fam. Nat. Syn. Monogr. 3: 152. 1847. TYPE: Unknown.

Phalacros Wenz., Linnaea 38: 164. 1874. TYPE: Phalacros cordatus (Mill.) Wenz. (=Crataegus phaenopyrum (L. f.) Medik.).

Key to the species of Crataegus

1. Flowers solitary or rarely 2-3 together; shrub to 2 m...Crataegus uniflora
1. Flowers in compound (rarely simple) cymes; plants often arborescent...2

2. Leaves with some of the primary lateral veins running to (or toward, forking just before) the sinuses as well as to the points of the lobes; flowers 0.7-1.3 cm wide...3
2. Leaves with the primary lateral veins running only to (or toward) the points of the lobes (if any); flowers often larger...4

3. Fruit 4-6 mm thick; thorns 2.5-6 cm long; styles and nutlets 1 (2 or 3)...Crataegus monogyna
3. Fruit 6-9 mm thick; thorns mostly 0.5-1.5 cm long; styles and nutlets 3-5...Crataegus phaenopyrum

4. Bracts of the corymb numerous, conspicuously and copiously stipitate-glandular on the margins; petioles glandular; corymbs and leaves essentially glabrous (or a few hairs on the veins above); corymbs few- (rarely more than 8-) flowered, somewhat simple or umbelliform...Crataegus intricata
4. Bracts of corymb usually few and/or the glands sparse or absent; petioles eglandular or the corymbs villous; leaves various; corymbs usually many-flowered...5

5. Nutlets with deep or shallow pits or depressions on their ventral surfaces; plants flowering in June or latter half of May...6
5. Nutlets plane, not pitted ventrally; plants flowering in April, May, or early June...7

6. Mature leaf blades somewhat coriaceous, thickened at margins, the veins usually rather deeply impressed above, glabrous to pubescent on both surfaces; corymbs, new branches, and petioles glabrous to sparcely villous; thorns 2.5-9.5 cm long, usually numerous...Crataegus succulenta
6. Mature leaf blades thin, the veins (except sometimes along the midrib) scarcely if at all impressed above, strigose above and usually pubescent beneath; branchlets of current year, and petioles all usually villous or lightly tomentose; thorns ca. 2.5-5 cm long...Crataegus calpodendron

7. Blades of at least the floreal leaves somewhat acute to broadly or (more commonly) narrowly tapered or cuneate at their bases...8
7. Blades of both floreal and vegetative leaves mostly broadly rounded, truncate, or subcordate at their bases...10

8. Blades (at least of floreal leaves) mostly elliptic to ovate, broadest at or below the middle, often somewhat definitely lobed, usually 1-1.5 times as long as broad, often thin...Crataegus chrysocarpa
8. Blades (especially the floreal leaves) mostly obovate to oblong-elliptic, broadest above or rarely at the middle, unlobed or very obscurely lobed near the apex, mostly 1.5-3 or more times as long as broad, usually thickish or coriaceous (except sometimes in the shade)...9

9. Leaves glossy above, the veins not (or only slightly) impressed; petioles mostly less than 1 cm long; styles and nutlets 1-3; stamens ca. 10 or 20...Crataegus crusgalli
9. Leaves dull above, the veins rather conspicuously impressed; petioles mostly 1-2 cm long; styles and nutlets 3-5; stamens ca. 20...Crataegus punctata

10. Corymbs, calyces, and leaves (at least along main veins) beneath somewhat densely villous-tomentose; fruits short-villous at least at the ends...11
10. Corymbs, calyces, and leaves glabrous or pubescent; fruits glabrous...12

11. Stamens ca. 10; fruit pyriform or obovoid...Crataegus submollis
11. Stamens ca. 20; fruit subglobose (ocassionally oblong-ovoid)...Crataegus mollis

12. Young leaves roughened above with short appressed hairs; stamens usually 10 or fewer; fruit with a small sessile calyx...13
12. Young leaves glabrous or pubescent; stamens 10 or 20; fruit with a large prominent calyx...14

13. Flowering corymbs more or less villous...Crataegus flabellata
13. Flowering corymbs glabrous...Crataegus macrosperma

14. Floreal leaves usually ovate or deltate; stamens 10-20; young leaves glabrous to pubescent above...Crataegus pruinosa
14. Floreal leaves usually oblong-ovate; stamens 10 or fewer; young leaves strigose above...Crataegus pedicellata

List of Crataegus Species

References to Crataegus

  • Akhunova, S. S. 1987. On systematic significance of pericarp anatomical characters in some members of the genus Crataegus (Rosaceae). Bot. Zhurn. (Moscow & Lenengrad) 72(6): 778-80. (In Russian)
  • Alexander, E. J. 1960. Crataegus chrysocarpa phoenicea. Addisonia 24: 7.
  • Angell, V. C. 1933. The Crataegi of Grand Rapids, Mighigan, and vicinity. Pap. Michigan Acad. Sci. 17: 1-50.
  • Anonymous 1887. Proceedings of the Club. Bull. Torrey Bot. Club 14: 88.
  • Anonymous 1892. Proceedings of the club. Bull. Torrey Bot. Club 19: 139-40.
  • Anonymous 1977. Dotted hawthorn, Crataegus punctata. Rose family (Rosaceae). Morton Arbor. Quart. 13(1): 15.
  • Ashe, W. W. 1899. New east American species of Crataegus. J. Elisha Mitchell Sci. Soc. 16: 70-9.
  • Beadle, C. D. 1900. Studies in Crataegus- I. Bot. Gaz. 28: 405-17.
  • Bessey, C. E. 1902. Multiplication of species in botany. Science 15: 795.
  • Boutineau, E. 1883. De la fleur des Rosacees. Contribution a l'etude des ovaires inferes. Paris. , 44 pages.
  • Brown, H. B. 1910. The genus Crateagus, with some theories concerning the origin of its species. Bull. Torrey Bot. Club 37: 251-60.
  • Burton, P. J.; Bazzaz, F. A. 1991. Tree seedling emergence on interactive temperature and moisture gradients and in patches of old-field vegetation. Amer. J. Bot. 78(1): 131-49.
  • Bush, B. F. 1912. The geographic origin of Crataegus viridis L. Rhodora 14: 81-6.
  • Camp, W. H. 1942. The Crataegus problem. Castanea 7(4-5): 51-5.
  • Camp, W. H. 1942. Ecological problems and species concepts in Crataegus. Ecology 23: 368-9.
  • Challice, J. S. 1981. Chemotaxonomic studies in the family Rosaceae and the evolutionary origins of the subfamily Maloideae. Preslia 53(4): 289-304. (Chech summary)
  • Christensen, K. I. 1982. A biometric study of some hybridising Crataegus populations in Denmark. Nordic J. Bot. 2: 537-48.
  • Corbet, S. A. 1979. Humidity, nectar and insect visits to flowers, with special reference to Crataegus, Tilia, and Echium. Ecol. Entomol. 4: 9-22.
  • Courtney, S. P.; Manzur, M. I. 1985. Fruiting and fitness in Crataegus monogyna: The effects of frugivores and seed predators. Oikos 44: 398-406.
  • Davis, W. E.; Rose, R. C. 1912. The effect of external conditions upon the after-ripening of the seeds of Crataegus mollis. Bot. Gaz. 54: 49-62.
  • Dickinson, T. A. 1985. The biology of Canadian weeds. 68. Crataegus crus-galli L. sensu lato. Canad. J. Pl. Sci. 65: 641-54.
  • Dickinson, T. A. 1995. The biology of Canadian weeds. 68. Crataegus crus-galli L. sensu lato. In: The Biology of Canadian Weeds. The Agricultural Institute of Canada, Ottawa, Ontario, Canada. , 76-89 pages.
  • Dickinson, T. A. 1983. Crataegus crus-galli L. sensu lato in southern Ontario: phenotypic variation and variability in relation to reproductive behavior. Ph.D. Dissertation Univ. Western Ontario, London, Ontario,
  • Dickinson, T. A. 1986. Topodeme differentiation in Ontario taxa of Crataegus (Rosaceae:Maloideae): leaf morphometric evidence. Canad. J. Bot. 64: 2738-47.
  • Dickinson, T. A.; Belaoussoff, S.; Love, R. M.; Muniyamma, M. 1996. North American black-fruited hawthorns: 1. Variation in floral construction, breeding system correlates, and their possible evolutionary significance in Crataegus sect. Douglasii Loudon. Folia Geobot. Phytotax. 31: 355-71.
  • Dickinson, T. A.; Phipps, J. B. 1986. Studies in Crataegus (Rosaceae: Maloideae) XIV. The breeding system of Crataegus crus-galli sensu lato in Ontario. Amer. J. Bot. 73: 116-30.
  • Dickinson, T. A.; Phipps, J. B. 1985. Studies in Crataegus L. (Rosaceae:Maloideae): XIII. Degree and pattern of phenotypic variation in Crataegus sect. Crus-galli in Ontario. Syst. Bot. 10(3): 322-37.
  • Dickinson, T. A.; Phipps, J. B. 1980. Correlated experimental and developmental studies of reproductive behavior in Crataegus crus-galli L. sensu lato. (Abstract)
  • Dickinson, T. A.; Phipps, J. B. 1984. Studies in Crataegus (Rosaceae: Maloideae). IX. Short-shoot leaf heteroblasty in Crataegus crus-galli sensu lato. Canad. J. Bot. 62: 1775-80.
  • Eggleston, W. W. 1906. Crataegus of Dutchess County, New York. Torreya 6: 63-7. (Also Bergen, Nassau, Putnam, & Westchester Cos.)
  • Eggleston, W. W. 1908. The Crataegi of the northeastern United States and adjacent Canada. Rhodora 10: 73-84.
  • Eggleston, W. W. 1908. The thorn trees, genus Crataegus L. In: North American Trees. Holt, New York. , 443-82 pages.
  • El-Gazzar, A. 1980. The taxonomic significance of leaf morphology in Crataegus (Rosaceae). Bot. Jahrb. Syst. 101: 457-69.
  • El-Gazzar, A.; Badawi, A. A. 1977. The taxonomic significance of chromosome numbers and geography in Crataegus L. Phytologia 35(4): 271-5.
  • Flemion, F. 1938. Breaking the dormancy of seeds of Crataegus species. Contr. Boyce Thompson Inst. Pl. Res. 9: 409-23.
  • Gorchov, D. L. 1987. Sequence of fruit ripening in bird-dispersed plants: consistency among years. Ecology 68: 223-5.
  • Gosler, A. G.; Kelly, C. K.; Blakey, J. K. 1994. Phenotypic plasticity in leaf morphology of Crataegus monogyna (Rosaceae): an experimental study with taxonomic implications. J. Linn. Soc. Bot. 115(3): 211-9.
  • Hoover, K. B. 1961. Hawthorn studies in Pennsylvania in relation to wildlife values.
  • Hunter, J. C.; Mattice, J. A. 2002. The spread of woody exotics into the forests of a northeastern landscape, 1938-1999. J. Torrey Bot. Soc. 129: 220-227.
  • Kruschke, E. P. 1955. The hawthorns of Wisconson. I. Status, objectives, and methods of collecting and preparing specimens. Milwaukee Public Mus. Publ. Bot. 2: 1-124.
  • Kruschke, E. P. 1965. Contributions to the taxonomy of Crataegus. Milwaukee Public Mus. Publ. Bot. 3: 1-273.
  • Lance, R. 1995. The hawthorns of the southeastern United States.
  • Leavitt, R. G. 1905. The defences of the cock-spur thorn. Pl. World 8: 239-44.
  • Lindenhofer, A; Weber, A 1999. The spiraeoid androecium of Pyroideae and Amygdaloideae (Rosaceae). Bot. Jahrb. Syst. 121: 583-605.
  • Lo, E. Y. Y. 2010. Fine-scale comparisons of genetic variability in seed families of asexually and sexually reproducing Crataegus (Hawthorn; Rosaceae). Amer. J. Bot. 97: 1014-1024.
  • Longley, A. E. 1924. Cytological studies in the genus Crataegus. Amer. J. Bot. 11: 295-317.
  • Macklin, J. A.; Phipps, J. B. 2006. Studies in Crataegus series Coccineae. I. Delimitation of series. Canad. J. Bot. 84: 70-86.
  • Macklin, J. A.; Phipps, J. B.; Boufford, D. E. 2000. Charles Sargnet's type concept: a guide to interpreting his names in Crataegus (Rosaceae). Harvard Papers in Botany 5: 123-128.
  • Manzur, M. I.; Courtney, S. P. 1984. Influence of insect damage in fruits of hawthorn on bird foraging and seed dispersal. Oikos 43: 265-70.
  • Muniyamma, M.; Phipps, J. B. 1979. Cytological proof of apomixis in Crataegus. Amer. J. Bot. 66(2): 149-55.
  • Muniyamma, M.; Phipps, J. B. 1984. Studies in Crataegus. XI. Further cytological evidence for the occurrence of apomixis in North American hawthorns. Canad. J. Bot. 62: 2316-24.
  • Muniyamma, M.; Phipps, J. B. 1985. Studies in Crataegus. XII. Cytological evidence for sexuality in some diploid and tetraploid species of North American hawthorns. Canad. J. Bot. 63: 1319-24.
  • Muniyamma, M.; Phipps, J. B. 1979. Meiosis and polyploidy of Ontario species of Crataegus in relation to their systematics. Canad. J. Genet. Cytol. 21(2): 231-41.
  • Myers, J. A. 2004. Seed dispersal by white-tailed deer: implications for long-distance dispersal, invasion, and migration of plants in eastern North America. Oecologia 139: 35-44.
  • Nash, G. V. 1919. Crataegus macrosperma. Addisonia 4: 35.
  • Nash, G. V. 1920. Crataegus phaenopyrum. Addisonia 5: 33.
  • Nash, G. V. 1919. Crataegus succulenta. Addisonia 4: 5-6.
  • Ode, B. 1996. Crataegus crus-galli L. Gorteria 22: 165-6. (In Dutch)
  • Palmer, E. J. 1925. Synopsis of North American Crataegi. J. Arnold Arbor. 6: 5-128.
  • Palmer, E. J. 1932. The Crataegus problem. J. Arnold Arbor. 13: 342-62.
  • Palmer, E. J. 1943. The species concept in Crataegus. Chron. Bot. 7: 373-5.
  • Palmer, E. J. 1946. Crataegus in the northeastern and central United States and adjacent Canada. Brittonia 5: 471-490.
  • Palmer, E. J. 1932. Crataegus arnoldiana Addisonia 17: 33-4. (= C. mollis)
  • Parrish, J. A. D.; Bazzaz, F. A. 1982. Niche responses of early and late successional tree seedlings on three resource gradients. Bull. Torrey Bot. Club 109(4): 451-6.
  • Phipps, J. B. 1983. Crataegus- A nomenclator for sectional and serial names. Taxon 32: 598-604.
  • Phipps, J. B. 1988. Crataegus (Maloideae, Rosaceae) of the southeastern United States, I. Introduction and series Aestivales. J. Arnold Arbor. 69(4): 401-31.
  • Phipps, J. B. 1984. Problems of hybridity in the cladistics of Crataegus (Rosaceae). In: Plant Biosystematics. Academic Press, Toronto. , 417-38 pages.
  • Phipps, J. B. 1988. Typification of Crataegus crus-galli L. (Rosaceae) and nomenclatural notes on some related species of hawthorn. J. Linn. Soc. Bot. 96(4): 359-69.
  • Phipps, J. B. 1981. Infra-generic ranks in Crataegus (Rosaceae).
  • Phipps, J. B. 1983. Biogeographic, taxonomic, and cladistic relationships between east asiatic and North American Crataegus. Ann. Missouri Bot. Gard. 70: 667-700.
  • Phipps, J. B. 1998. Synopsis of Crataegus series Apiifoliae, Cordatae, Microcarpae, and Brevispinae, (Rosaceae subfam. Maloideae). Ann. Missouri Bot. Gard. 85: 475-491.
  • Phipps, J. B. 2005. A review of hybridization in North American hawthorns- another look at "the Crataegus problem". Ann. Missouri Bot. Gard. 92: 113-126.
  • Phipps, J. B. 2006. Crataegus series Parvifoliae and its putative hybrids in the southeastern United States. Sida 22: 423-445.
  • Phipps, J. B. 2007. Miscellaneous typifications, new combinations and one new variety in North American Crataegus (Rosaceae). J. Bot. Res. Inst. Texas 1: 1005-1010.
  • Phipps, J. B. 2007. Kruschke names in North American Crataegus (Rosaceae). J. Bot. Res. Inst. Texas 1: 1011-1014. (for a correction and clarification see: J. Bot. Res. Inst. Texas 2:473. 2008.)
  • Phipps, J. B. 2008. Kruschke names in North American Crataegus (Rosaceae): a correction and clarifications. J. Bot. Res. Inst. Texas 2: 473.
  • Phipps, J. B.; Cafferty, S.; Macklin, J. A. 2003. Lectotypification of Crataegus coccinea L. and its conspecificity with C. pedicellata Sarg. (Rosaceae). Taxon 52: 337-338.
  • Phipps, J. B.; Muniyamma, M. 1980. A taxonomic revision of Crataegus (Rosaceae) in Ontario. Canad. J. Bot. 58: 1621-99.
  • Phipps, J. B.; Robertson, K. R.; Rohrer, J. R.; Smith, P. G. 1991. Origins and evolution of subfam. Maloideae (Rosaceae). Syst. Bot. 16: 303-32.
  • Phipps, J. B.; Smith, P. G.; Rohrer, J. R. 1990. A checklist of the subfamily Maloideae (Rosaceae). Canad. J. Bot. 68: 2209-69. (French summary)
  • Power, N. 1980. Crataegus-insect relationships. , Unpubl. honours thesis Univ. Western Ontario, London, Ontario,
  • Rhoads, A. F.; Meyer, P. W.; Sanfelippo, R. 1981. Performance of urban street trees evaluated. J. Arboric. 7: 127-132.
  • Rickett, H. W. 1936. Forms of Crataegus pruinosa. Bot. Gaz. 97: 788-93.
  • Rickett, H. W. 1943. The inflorescence of Crataegus. Bull. Torrey Bot. Club 70: 489-95.
  • Rickett, H. W. 1937. Forms of Crataegus crus-galli. Bot. Gaz. 98: 609-16.
  • Robertson, C. 1894. Flowers and insects: Rosaceae and Compositae. Trans. St. Louis Acad. Sci. 6: 435-80.
  • Robertson, K. R.; Phipps, J. B.; Rohrer, J. R. 1992. Summary of leaves in the genera of Maloideae (Rosaceae). Ann. Missouri Bot. Gard. 79: 81-94.
  • Robertson, K. R.; Phipps, J. B.; Rohrer, J. R.; Smith, P. G. 1991. A synopsis of genera in Maloideae (Rosaceae). Syst. Bot. 16: 376-94.
  • Rohrer, J. R.; Robertson, K. R.; Phipps, J. B. 1991. Variation in structure among fruits of Maloideae (Rosaceae) Amer. J. Bot. 78: 1617-35.
  • Sallabanks, R. 1992. Fruit fate, frugivory, and fruit characteristics: a study of the hawthorn, Crataegus monogyna (Rosaceae). Oecologia 91: 296-304.
  • Santamour, F. S. 1983. Woody-plant succession in the urban forest: filling cracks and crevices. J. Arboric. 9(10): 267-70. (Woody spp. on abandoned brick kilns)
  • Sargent, C. S. 1921. Notes on North American trees. IX. New species and varieties of Crataegus. J. Arnold Arbor. 3: 1-11.
  • Sargent, C. S. 1922. Notes on North American trees. X. New species and varieties of Crataegus. J. Arnold Arbor. 3: 182-206.
  • Sargent, C. S. 1923. Notes on North American trees. XI. New species of Crataegus. J. Arnold Arbor. 4: 99-107.
  • Sargent, C. S. 1925. Notes on Crataegus-Crataegus padifolia var. incarnata. J. Arnold Arbor. 6: 1-5.
  • Sargent, C. S. 1907. The genus Crataegus in North America. J. Bot. 45: 289-92.
  • Sargent, C. S. 1903. Recently recognized species of Crataegus in eastern Canada and New England. Rhodora 5: 52-66.
  • Sargent, C. S. 1903. Recently recognized species of Crataegus in eastern Canada and New England, -II-V. Rhodora 5: 108-18, 137-53, 159-68, 182-7.
  • Sargent, C. S. 1905. Recently recognized species of Crataegus in eastern Canada and New England, -VI. Rhodora 7: 162-4, 174-85, 192-219.
  • Sargent, C. S. 1909. American Crataegi in the Species Plantarum of Linnaeus. Rhodora 11: 181-3.
  • Sargent, C. S. 1901. Notes on Crataegus in the Champlain Valley. Rhodora 3: 19-31.
  • Sherburne, J. A. 1972. Effects of seasonal changes in the abundance and chemistry of the fleshy fruits of northeastern woody shrubs on patterns of exploitation by frugivorous birds. Ph.D. Dissertation Cornell University, Ithaca, NY157 p.
  • Sinnott, Q. P.; Phipps, J. B. 1983. Variation patterns in Crataegus series Pruinosae (Rosaceae) in Ontario. Syst. Bot. 81: 59-70.
  • Smith, P. G.; Phipps, J. B. 1988. Studies in Crataegus (Rosaceae, Maloideae): 19. Breeding behavior in Ontario Crataegus series Rotundifoliae. Canad. J. Bot. 66: 1914-23.
  • Smith, P. G.; Phipps, J. B. 1988. Studies in Crataegus (Rosaceae, Maloideae): 15. Patterns of morphological variation in Crataegus series Rotundifoliae in Ontario. Syst. Bot. 13(1): 97-106.
  • Smith, P. G.; Phipps, J. B. 1987. Studies in Crataegus (Rosaceae, Maloideae): 16. Taxonomy of C. series Rotundifoliae in Ontario. Canad. J. Bot. 65: 2646-67.
  • Smith, P. G.; Phipps, J. B.; Dickinson, T. A. 1980. Accumulated heat in relation to Crataegus flowering. (Abstract)
  • Southwick, E. E. 1981. Nectar production composition energetics and pollinator attractiveness in spring flowers of western New York USA. Amer. J. Bot. 68: 994-1002.
  • Standish, L. M. 1916. What is happening to the hawthorns? J. Heredity 7: 266-79.
  • Sterling, C. 1964. Comparative morphology of the carpel in the Rosaceae III. Pomoideae: Crataegus, Hesperomeles, Mespilus, Osteomeles. Amer. J. Bot. 51: 705-12.
  • Stoll, R. J. 1980. Foods of ruffed grouse Bonasa umbellus in Ohio USA. Ohio Fish Wildlife Rep. 1980: 1-18.
  • Sutton, S. B. 1970. Crataegus: a thorny problem. In: Charles Sprague Sargent and the Arnold Arboretum. Harvard Univ. Press, Cambridge, MA. , 279-98 pages.
  • Talent, N.; Dickinson, T. A. 2005. Polyploidy in Crataegus and Mespilus (Rosaceae, Maloideae): evolutionary inferences from flow cytometry of nuclear DNA amounts. Canad. J. Bot. 83: 1268-1304.
  • Talent, N.; Dickinson, T. A. 2007. The potential for ploidy level increases and decreases in Crataegus (Rosaceae, Spiraeoideae, tribe Pyreae). Canad. J. Bot. 85: 570-584.
  • Thomas, W. W.; Boufford, D. E. 1986. C.S. Sargents's Crataegus (Rosaceae) types from western Pennsylvania. Brittonia 38: 27-31.
  • Ulf-Hansen, P. F. 1988. An examination of large-scale population changes in eastern North American hawthorns. M.S. Thesis Univ. Western Ontario, London, Ontario,
  • Voss, E. G. 1965. A review on Crataegus. Michigan Bot. 4: 93-6.
  • Wells, T. C. 1985. An analysis of interserial hybrids in Crataegus. M.S. Thesis Univ. Western Ontario, London, Ontario,
  • Wells, T. C.; Phipps, J. B. 1989. Studies in Crataegus (Rosaceae: Maloideae): 20. Interserial hybridization between Crateagus monogyna (series Oxycanthae) and Crataegus punctata (series Punctatae) in southern Ontario. Canad. J. Bot. 67: 2465-72. (French summary)
  • Werner, P. A.; Harbeck, A. L. 1982. The pattern of tree seedling establishment relative to staghorn sumac cover in Michigan old fields. Amer. Midl. Naturalist 108: 124-32.
  • Weryszko-Chmielewska, E. 2003. Characteristics of floral nectaries and nectar in two species of Crataegus (Rosaceae). Pl. Syst. Evol. 238: 33-41.