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Polysiphonia subtilissima

The filamentous Rhodophytes can be very frustrating to identify definitively. This individual happens to be growing epiphytically on another Rhodophyte, the invasive Grateloupia doryphora. This alga is a member of the genus Polysiphonia. "Poly-" means many, an "siphon" means tube. So, members of this genus are composed of many tubes. This particular species has four tubes, so that when viewing a cross section, we see four pericentral cells (peri = around). This species also has trichoblasts or hairs that grow from the tips of branches as seen here. This particular specimen is a female gametophyte on which is growing another generation called the carposporophyte, also seen here.

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