The Collaborative International Dictionary
Crataegus tomentosa
Blackthorn \Black"thorn`\, n. (Bot.)
A spreading thorny shrub or small tree ( Prunus spinosa), with blackish bark, and bearing little black plums, which are called sloes; the sloe.
A species of Crat[ae]gus or hawthorn ( Crat[ae]gus tomentosa). Both are used for hedges.