What is the meaning of Whitethorn?

Crataegus monogyna, a hawthorn species native to Europe, northwest Africa and western Asia.

Bursaria spinosa, a small Australian shrub.

Vachellia constricta, formerly Acacia constricta, whitethorn acacia, a shrub in the family Fabaceae.

Senegalia polyacantha, of India

Ceanothus leucodermis, chaparral whitethorn, a shrub in the family Rhamnaceae.

Source: wiktionary.org