Family Description:
Macroscopic plants are tubular, saccate, or foliose. This phase represents the gameto-phyte, which bears only plurilocular reproductive structures. In some species, this phase alternates with a crustose phase that resembles Ralfsia and bears the unilocular reproductive structures. Such crusts are assumed to represent the sporophytic phase in the life history of such species. Cells contain only a single chloroplast, which contains a prominent pyrenoid.

Species description:
The thallus is globular in shape and can grow to at least 7 cm (almost 3 in) in diameter. It is attached rather more narrowly at the base than are other species of this genus. Like other species of Colpomenia it is solid when young and then becomes hollow with age and at that time is rather thin-walled and smooth. It has clusters of colorless hairs on the surface, and when the reproductive organs appear, they are at first located near these hair tufts, but later spread to other areas. The thallus becomes greenish if it has time to dry at low tide.

This species grows either directly on rocks or epiphytically on other algae (such as articulated corallines) which, in turn, grow on rocks. In southern California, in places where rocky habitats are subjected to frequent sand scour, Bulb Seaweed cannot grow directly on rocks but only epiphytically. C. peregrina is an invasive species and was introduced to Europe in the first quarter of the twentieth century, where it spread rapidly. This invasive habit is indicated by the specific name, peregrina, which means "wandering."

As in other species of saccate algae, the seawater that is retained within the tissues during low tide greatly reduces desiccation. This alga lacks a cuticle, and loses water rapidly for fifteen minutes when first emersed but not thereafter. When reimmersed, water can enter the tissues through microscopic pits that are scattered over the surface.

Source:  North Pacific Seaweeds

Synonyms and Alternate Names:
Colpomenia sinuosa var. peregrina