A family of brown seaweeds, which includes a single genus, Himanthalia. The plant lives for 2 years. During the first year a stalked, disc-like thallus is formed: this measures several centimetres across. In the second year 1–4 long, strap-like branches grow from the disc, and these bear the conceptacles within which gametes are formed. There is 1 British species, H. elongata (sea thong), found at or near the low-water mark on exposed shores.
Subjects: Plant Sciences and Forestry.