Marine Animal Encyclopedia
Small jelly weed Gelidium foliaceum
There are many species of Gelidium worldwide, and they are difficult to identify because the plants can look very different depending on their habitat and whether they have been grazed by seashore animals such as limpets. Ongoing work on molecular sequencing is gradually resolving some of these problems, and Gelidium foliaceum is one species that has recently been reclassified. It has a flattened, much lobed and curled frond, which grows in dense clumps on rocky seashores. The fronds are tough and cartilaginous, and the seaweed is attached to the rock at frequent intervals by small hairlike structures, or rhizoids, from a creeping stem, or stolon. This creeping habit is probably the main method of spreading, but some species of Gelidium also reproduce sexually. Species of Gelidium are the main source of agar (see Seaweed jelly).
Red seaweeds have long been collected for making jellies, and agar (extracted from species of Gelidium, Gracilaria, and Pterocladia) is used for the preparation of gels on a large scale. Agar gel is used as a medium for growing fungi and bacteria in microbiological investigations, and in the food industry for producing jam and conserving meat and fish.