Halidrys siliquosa is a large marine brown algae.
Halidrys siliquosa is a large brown alga growing to a length of . The fronds are somewhat flattened, tough and leathery. They and less than 1 cm broad. The branches occur alternately arranged in one plane. Air bladders occur and are oblong and pointed. The plants are attached by a discoid holdfast.
The plants are hermaphroditic, bearing bisexual conceptacles appearing as pods on stalks at the end of branches.
Generally found around Ireland, Great Britain - including Shetland and the Isle of Man.
Low level, low littoral, rock pools.