Stephanocystis dioica
Halidrys dioica
Geographic Range 3
Stephanocystis dioica is found from Redondo Beach, California to northern Baja California Sur. It is found in the lower intertidal zone and subtidally.
Morphology and Identifying Characteristics 3
Stephanocystis dioica is a large, lower intertidal to subtidal seaweed. It is usually brown on the lower branches, lightening to tan on the upper branches. It has tough, pinnately branched blades and an almost woody lower stipe. When it is reproductive, S. dioica has conspicuous receptacles resembling air bladders on its upper branches. The receptacles are produced in a chain, the whole receptacle resembling a flattened pea-pod.
This species is often confused with its congener, S. osmundacea, 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. dioica has singly pinnate and more rounded branches that appear more entire, while S. osmundacea has bi-pinnate branching that makes it appear more fern-like and dissected. 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 receptacles of Sargassum sp. do not form in chains.
Life History 3
Stephanocystis dioica is a dioecious perennial seaweed. Unlike other brown algae, S. dioica (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.
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- cppmarinebotany1, no known copyright restrictions (public domain)
- (c) cppmarinebotany1, some rights reserved (CC BY-SA)
