- Scientific name: Crataegus bicknellii
- Species of Greatest Conservation Need (MA State Wildlife Action Plan)
- Endangered (MA Endangered Species Act)
Description
Bicknell’s hawthorn is a small, shrubby tree (up to 3 m [10 ft] tall) in the rose family (Rosaceae) known only from Nantucket Island. It has numerous long (2–6 cm [0.79-2.4 in]) thorns along its branches, with egg-shaped leaf blades that taper to the base and have double-toothed margins. Five-petaled flowers are produced around mid-May in a flat-topped cluster. The round, red fruit is between one-quarter and one-half inch in diameter and contains 4 to 5 “nutlets” within the soft flesh.
The genus Crataegus is complex and a technical manual must be consulted for proper identification. Bicknell’s hawthorn is best identified using a hand lens or microscope to examine the flowers and nutlets. The flowers are hairless, have 5 to 10 stamens with purplish anthers, and 4 or 5 styles. The calyx lobes are covered with minute glands and have long, pointed teeth. The inner surface of the nutlets can appear smooth or have small erosions.
Reports of Bicknell’s hawthorn in Barnstable County were recently determined to be long-thorned hawthorn (C. macracantha), which also occurs in coastal plain habitats. Long-thorned hawthorn has 8 to 31 flowers per inflorescence and nutlets with distinctive depressions on the inner face. In contrast, Bicknell’s hawthorn has fewer flowers per inflorescence and nutlets with mostly smooth inner surfaces (some erosions may be present). Frosted hawthorn (C. pruinosa) is also found on the coastal plain in Massachusetts. This species has two recognized varieties in New England: Crataegus pruinosa var. porteri and Crataegus pruinosa var. pruinosa. Differentiating between Bicknell’s hawthorn and frosted hawthorn requires close examination of the flowers: Bicknell’s hawthorn has 5 to 10 stamens whereas frosted hawthorn has 12 to 20 stamens.
Life cycle and behavior
Five-petaled flowers are produced around mid-May in a flat-topped cluster.
Population status
Bicknell’s hawthorn is listed under the Massachusetts Endangered Species Act as Endangered. All listed species are protected from killing, collecting, possessing or sale, and from activities that would destroy habitat and thus directly or indirectly cause mortality or disrupt critical behaviors. The MassWildlife’s Natural Heritage & Endangered Species Program database has 7 records from Nantucket County. 2 of these records have been observed within the last 25 years.
Distribution and abundance
Until recently, the taxonomy of Bicknell’s hawthorn was unclear, resulting in much uncertainty about its range and status. The only known occurrences for Bicknell’s hawthorn are on Nantucket Island, Massachusetts.
Distribution in Massachusetts
1999-2024
Based on records in the Natural Heritage Database
Habitat
Bicknell’s hawthorn is known from woodlands, roadsides, and field edges. Extant populations on Nantucket Island are located in dense shrub thickets near roadsides. Species found growing in association with Bicknell’s hawthorn include shadbush (Amelanchier spp.), Virginia creeper (Parthenocissus quinquefolia), black cherry (Prunus serotina), scrub oak (Quercus ilicifolia), sassafras (Sassafras albidum), highbush blueberry (Vaccinium corymbosum), arrowwood (Viburnum dentatum), and fox grape (Vitis labrusca).
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Threats
Lack of regeneration and competition from aggressive woody plants are the two greatest management concerns for extant populations of Bicknell’s hawthorn. Fox grape, a species native to Nantucket, is an aggressive woody vine that may pose the greatest threat to Bicknell’s hawthorn at this time. Fox grape is capable of out-competing woody plants by growing over the tops of small trees and shrubs and shading the vegetation beneath.
Conservation
Sites supporting populations of Bicknell’s hawthorn should be monitored regularly, and native and non-native woody competitors should be removed to reduce competition. Regeneration of Bicknell’s hawthorn is limited at known populations, and saplings that become established are at risk due to deer browse. Fencing around individual plants may be necessary to allow saplings to mature to adulthood. All active management of rare plant populations (including clearing, fencing, and invasive species removal) is subject to review under the Massachusetts Endangered Species Act and should be planned in close consultation with MassWildlife’s Natural Heritage & Endangered Species Program.
References
Haines, A. 2011. Flora Novae Angliae – a Manual for the Identification of Native and Naturalized Higher Vascular Plants of New England. New England Wildflower Society, Yale Univ. Press, New Haven, CT.
Contact
| Date published: | April 14, 2025 |
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