The sea-buckthorns are deciduous

Deciduous

Deciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe...

 shrub

Shrub

A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...

s in the genus Hippophae, family Elaeagnaceae

Elaeagnaceae

Elaeagnaceae, the oleaster family, is a plant family of the order Rosales comprising small trees and shrubs, native to temperate regions of the Northern Hemisphere, south into tropical Asia and Australia. The family has 45-50 species in three genera....

. The name sea-buckthorn is hyphenated here to avoid confusion with the buckthorn

Buckthorn

The Buckthorns are a genus of about 100 species of shrubs or small trees from 1-10 m tall , in the buckthorn family Rhamnaceae...

s (Rhamnus, family Rhamnaceae

Rhamnaceae

Rhamnaceae, the Buckthorn family, is a large family of flowering plants, mostly trees, shrubs and some vines.The family contains 50-60 genera and approximately 870-900 species. The Rhamnaceae have a worldwide distribution, but are more common in the subtropical and tropical regions...

). It is also referred to as sandthorn, sallowthorn, or seaberry.
There are considered to be seven species, two of them probably of hybrid origin, native over a wide area of Europe and Asia.

The common sea-buckthorn

Hippophae rhamnoides

Hippophae rhamnoides, the common sea-buckthorn, is a deciduous shrub species in the genus Hippophae.Common Sea-buckthorn branches are dense, stiff, and very thorny. The leaves are a distinct pale silvery-green, lanceolate, 3-8 cm long and less than 7 mm broad. It is dioecious, with male and female...

 (Hippophae rhamnoides) is by far the most widespread of the species in the genus, with the ranges of its eight subspecies extending from the Atlantic coasts of Europe right across to northwestern China.