Stephanocystis osmundacea
Cystoseira osmundacea, chain bladder kelp
Geographic Range 4
Stephanocystis osmundacea is found along the Pacific coast of North America, from Northern Oregon down to Northern Baja California, Mexico. It is found in the low intertidal zone and subtidally in kelp forests.
Morphology and Identifying Characteristics 4
Stephanocystis osmundacea is a large, lower intertidal to subtidal seaweed. It is usually dark brown on the lower branches, lightening to tan on the upper branches. It has tough, bipinnately branched blades and an almost woody stipe. When it is reproductive, S. osmundacea has conspicuous receptacles resembling air bladders on its upper branches. The receptacles are produced in a chain, with each spherical chamber very apparent and distinct.
This species is often confused with its congener, S. dioica, and it can be difficult to tell them apart, particularly when they are vegetative. It is easiest to tell them apart when they are reproductive and have developed receptacles. The chambers of the receptacles of S. dioica are much less well defined than those of S. osmundacea, and resemble more of a pea-pod shape. The receptacles of S. osmundacea resemble the "peas without the pod".
In addition, the branching pattern of the thallus is different between the two species, at least in the populations of S. osmundacea south of Point Conception. S. osmundacea has bi-pinnate branching that makes it appear more fern-like and dissected, while S. dioica has singly pinnate and more rounded branches that appear more entire.
This species may also be confused with another fucoid genus, Sargassum, but the branches of Sargassum sp. are not nearly as broad as those of Stephanocystis, and the pneumatocysts of Sargassum sp. do not form in chains.
Life History 4
Stephanocystis osmundacea is a dioecious perennial seaweed. Unlike other brown algae, S. osmundacea (order Fucales) does not undergo alternation of generations, but has a diplontic life cycle. It produces sperm and (usually) 1 non-motile egg within the conceptacles (cavities on the receptacle). These gametes unite, forming a zygote, which then begins developing into the adult thallus after ~2 months.
It has more complex tissue than some other phaeophytes, in that it has medullary, cortex, and meristoderm (structural/epidermal) cells. It has trumpet hyphae in its medulla to facilitate transport of photosynthates to the apical meristem.
Ecology 4
Stephanocystis osmundacea is found subtidally in Macrocystis pyrifera forests, comprising a part of the understory community in these ecosystems.
Sources and Credits
- (c) cppmarinebotany1, all rights reserved
- cppmarinebotany1, no known copyright restrictions (public domain)
- (c) intertidalecologist, all rights reserved, uploaded by intertidalecologist
- (c) cppmarinebotany1, some rights reserved (CC BY-SA)
