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Description
The typical feather-like branched filament lacks normal cross-walls and is essentially unicellular. Thus, a typical plant represents one cell up to 15 cm (6 in) long and is branched. These giant cells could “bleed” to death if they broke. Bryopsis overcomes this problem by taking protein bodies from throughout the cell and moving them quickly to the point of break in order to seal the rupture. Scientists have exploited these giant cells by conducting unique hybridization experiments. The pro-cedure is to squeeze the protoplasm from each of two differ-ent morphological forms and mix them together. The resulting plant (a hybrid) contains nuclei representing the different morphologies in the same cell. The form taken by this engineered plant will reveal which morphology is gen-etically dominant, or if neither is dominant, which would result in an intermediate morphology.
Habitat & Distribution
Plants are found on rocks, shells and wood in the lower intertidal region from BC to Mexico.
Bryopsis sp.
Bryopsis corticulans and detail of a large cell (left).
60 | Blades
Pacific Seaweeds
Blades
The blade morphology is common among the major seaweed groups. In the green seaweeds, the blades are usually one or two cells thick. The blade’s thickness as well as its other dimensions are determined by the pattern of cell division. A game biologists play is to arrange species on the basis of morphological criteria. For example, one could establish a simple-to-complex lineage for some of the common green seaweeds. Imagine the green seaweed cell as being a cube. In an unbranched filament, this cube can divide in one plane only, resulting in a longer filament (Rhizoclonium, p. 52). In branched forms, the cube can occasionally divide in a second plane, giving rise to branches (Cladophora, p. 56). More or less equal cell divisions in two planes would result in a blade one cell thick (Prasiola, p. 61). Cell division limited to once in one plane, accompanied by equal and many cell divisions in two planes, would result in a blade two cells thick (bladed Ulva, p. 62). In some forms the two cell layers become disconnected, resulting in a hollow tube or sac (cylindrical Ulva, p. 66). Finally, the sac may tear, producing a blade one cell thick (Ulvaria, p. 64). Such an exercise may not contribute to our understanding of evolution, but it is instructive in appreciating how various forms come about.
Green blades of Ulva sp. in the high intertidal zone of Asilomar Beach, CA.
Green Seaweeds | 61
Identifying Pacific Seaweeds
Prasiola (short sea lettuce) p. 61
Ulva (sea lettuce) p. 62
Ulvaria / Kornmannia / Monostroma (dark sea lettuce) p. 64
Prasiola Short sea lettuce
Class Trebouxiophyceae Order Prasiolales Family Prasiolaceae
Number of Species
More than 30 species of Prasiola (Greek=green) are found worldwide, 5 locally: P. linearis, P. crispa, P. borealis, P. delicata and P. meridionalis.
Description
Prasiola is a very small bladed seaweed, at most a few centimetres in length and usually one cell thick. Tufts of these blades resemble little cabbages.
Prasiola can tolerate and exploit high-nitrogen conditions that most plants would find toxic. Mike Guiry (University College, Galway, Ireland) described the distribution of this group in Galway as being associated with telephone poles
Prasiola sp. and a convenient source of nitrogen, in Santa Cruz, CA.
62 | Blades
Pacific Seaweeds
employed by the local canine population, and in one case with a pole behind a pub. Check your neighbourhood watering holes for this telltale species.
Habitat & Distribution
Species of Prasiola in our area are found growing on wood or rock above the high tide level or along freshwater streams. A unique aspect of their distribu-tion is their association with guano of marine birds. Locally, these plants are distributed from Alaska to central California.
Ulva Sea lettuce
Class Ulvophyceae Order Ulvales Family Ulvaceae
Number of Species
Ulva (Latin=marsh plant) contains a stunning 128 species and forms world-wide. Locally, it is represented by about 15 species, of which at least 8 develop into flat blades. Common species in our area include U. californica, U. “lactuca,” U. lobata, U. rigida, U. stenophylla and U. taeniata.
Description
In 2003, molecular studies collapsed Ulva and Enteromorpha into one genus: Ulva. We retain two entries for the genus here; see p. 66 for discussion of cylindrical forms.
Bladed
