Gelidium vagum is a red alga, often with a treelike appearance, in which one, or several vertical trunk-like axes arise from a basal axis, with widely spaced short branchlet/. The trunks can reach 100 mm tall, but are usually shorter. The color ranges from yellowish red through brighter red to brownish red. This plant has an alternating life cycle with asexual tetrasporophytic plants and sexual gametophytic plants. This seaweed is native to the Northwest Pacific, from Pacific Russia to the Yellow Sea. on China. In 1984, it was collected on Denman island. in British Columbia, in areas where the Pacific Oyster (Magallana = Crassostrea gigas) was cultured. In 1996, it was collected in US waters, in the San Juan Islands and Bellingham Bay. It was also found in Tomales Bay, California Bay, where it was probably transferred with Pacific Oysters from British Columbia or Washington.