Taxonomy is often problematic and somewhat arbitrary; it does not always reflect evolutionary relationships and clades are often paraphyletic. It can, however, be a useful way to discuss shared features among organisms, and current work is helping to more accurately assign groupings. Click on the links to find out why Polysiphonia has been placed in each taxonomic group:
Perhaps the most problematic part of Polysiphonia’s taxonomy is at the kingdom level. Polysiphonia, and all algae, are traditionally placed within the kingdom Protista. This group is catch-all for all eukaryotes (having larger cells with a nucleus, organelles and a cytoskeleton) which are not plants, animals or fungi, but is not a monophyletic group (having one common ancestor). Others argue that the kingdom Protista should only include single-celled organisms, and that macroscopic algae should be placed in the kingdom Plantae. As a result of this confusion, many have abandoned the use of kingdoms altogether; in this case, Polysiphonia and all algae are placed within the domain Eukarya, which includes everything with eukaryotic cells.
Polysiphonia is included in the division Rhodophyta because it contains the photosynthetic pigment phycoerythrin (shown right), a type of phycobilin. Phycoerythrin gives it its red color and allows it to photosynthesize in deeper water. Like all reds, Polysiphonia has floridean starch as a storage product. Aspects of the life history of Polysiphonia also helps place it in the Rhodophyta; its oogamous sexual reproduction involving non-motile female carpogonium and non-flagellated male spermatia is typical of the reds. In fact, there are no flagellated stages in any part of the life cycles of the Rhodophyta.
Polysiphonia is a member of the subclass Florideophycidae because all of its cells (except for apical and reproductive cells) are multinucleated and numerous discoid chloroplasts are found in the cell peripheries. Florideophycidae (and Polysiphonia) are multicellular and have apical cell division, unlike Bangiophycidae, the other subclass within the Rhodophyceae. Also, Polysiphonia has prominent pit connections between adjacent cells, a characteristics common to the Florideophycidae.
The Order Ceramiales, which includes Polysiphonia, is defined by certain aspects of its reproduction and life history. All females of the order Ceramiales have 4-celled carpogonial branches, one carpogonial branch produced per supporting cell. In Polysiphonia (and Ceramiales) the carposporophyte develops from the auxiliary cell. Ceramiales have isomorphic sporophytes and gametophytes, and the gametophytes are dioecious. Ceramiales tetrosporangia can be cruciate or tetrahedral; Polysiphonia’s are tetrahedral.
The Family Rhodomelaceae contains 100 genera, including Polysiphonia, making it the largest family of reds. Much of this family is defined by its morphology. This family has polysiphonous construction. Members have four to 24 pericentral cells which form so that the last one to cut off from the axial cell is opposite the first one formed. Pericentral cells are equal in length to the axial cells. In Polysiphonia and all of Rhodomelaceae, branching is monopodial and mostly exogenous. Trichoblasts are exogenous and bear the sexual organs. During fertilization, the carpogonium fuses directly with the auxiliary cell.
There are more than 150 species of Polyisphonia. Features which define the group are found through out this website; here are just a few of their prominent characteristics. All members of the genus Polysiphonia have erect thalli (bodies), are reddish-brown to reddish-black in color and have radial branching. Trichoblasts are often deciduous and leave persistent scar cells at attachment points. Apical cells cut off proximal segments; these elongate and cut off pericentral cells of the same length as the central axial cell, creating one “tier,” or segment. Tetrasporangia are formed one per segment on the tetrsporophyte.
Specimens in this study were collected at various locations in Monterey Bay, including Hopkins Marine Life Refuge, Monterey Bay Harbor Marina, and Pebble Beach. It is difficult to distinguish between Polysiphonia species, however, a list of possible species of the specimens used and pictured in this study was compiled. The list consists of species explicitely listed as occuring in Monterey Bay, as well as species whose listed range along the California coast includes the bay. Thus, this list probably errs on the side of being too inclusive.
four pericentral cells:
More than 4 pericentral cells:
One quick way to narrow the number of possible species for a particular specimen is to look at the pericentral cells. If only two complete, or perhaps one and two halves, pericentral cells per segment are visible from one side, the Polysiphonia probably only has four pericentral cells total.