Crataegus douglasii
   Includes distribution and occurrence, botanical and ecological characteristics, value and use, and fire ecology.
   http://www.fs.fed.us/database/feis/plants/shrub/cradou/

Crataegus douglasii (Black Hawthorn)
   Photos and brief description.
   http://www.cwnp.org/photopgs/cdoc/crdouglasii.html

Crataegus monogyna
   images
   http://www.dipbot.unict.it/orto/0298-1.html

Hawthorn: Crataegus monogyna
   Photographs of this tree, its buds, bark, leaves and inflorescence.
   http://www.plant-identification.co.uk/skye/rosaceae/crataegus-monogyna.htm