Oleaster
prickly shrub
mesquite
Barberry
Horizontal scrub
Chaparral is a thorny shrub native to North American prairies.
Sounds like a Berberis.
An aspalathus is any of the genus Aspalathus of flowering plants, or a thorny shrub yielding a fragrant oil.
A barberry is a thorny shrub of the genus Berberis, which bears yellow flowers and red or blue-black berries.
An andromeda is a shrub of the genus Pieris with small leathery leaves and small flowers. Alternatively, it is another name for bog rosemary.
There are 14 species of Bougainvillia, both evergreen shrubs, trees and thorny climbers that are evergreen or partly deciduous.
The woody evergreen shrub may grow to 15 ft (4.5 m) with flat gray-green leathery leaves. Dioecious, the female shrub with small flowers grows into green fruit and a wrinkled brown soft skin seed. And more . . .
If you cut a Eucalyptus back to ground level in the spring it will grow as a shrub and show juvenile foliage, let it grow and it will quickly become a tree.