Monterey Bay Aquarium Research Institute
Marine Botany

Plocamium Physical Characteristics

The thalli is erect with sympodial branching, and cross-sections of the thalli are elliptical. The ramuli (or branchlets) are unilateral and branch pectinately with between two and five (usually between 3 and 4) ramuli per pectination. The branches are compressed to strongly flattened, and show apical cell division with cells becoming progressively larger toward the interior. Each cell of the axial filaments has two lateral filaments. Above the last axial filament, the cells get progressively smaller toward the terminus eventually ending in a cortex with the apical cell at the tip.

New Zealand species show a possible seasonal alteration between tetrasporophyte and gametophyte generations (South, 1979). However, the author has observed both phases simultaneously during February and March, 1996, around the Monterey Peninsula, California.

The Californian species (which the author knows best) are dominated by P. cartilageneum, and include P. oregonum, and P. violaceum. Also associated with the Californian Plocamium species is the closely related (same family), Plocamiocolax pulvinata, which grows as an epiphyte on P. cartilageneum, and the genus Microcladia, which can be mistaken for Plocamium but is actually in the Ceramiales. In California, the total percentage cover probably varies little throughout the year, but Plocamium biomass (like the biomass of most of the Rhodophyta) hits a minimum in winter, both subtidally and intertidally (Cole, 1990).

Pigments of Plocamium include: r-Phycocyanin, Allophycocyanin, c-Phycorythrin, alpha- and beta-carotene, Chlorophyll a, and the cryptic Chlorophyll d. The genus Plocamium stores photosynthate as Floridean starch. The maximum elongation rate for Plocamium cartilageneum is 0.55 mm/day (Kain, 1987a, p. 469).

Taxonomy of the genus Plocamium is Class Rhodophyta, Subclass Florideophycidae, Order Plocamiales, and Family Plocamiaceae.

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