Monterey Bay Aquarium Research Institute
Marine Botany

Ceramium: Morphology

Cortex
One of the first things you might notice when first looking at Ceramium in the field is that it usually appears striped. This is due to a special pattern of cortication found in Ceramium and related genera. The main branches of the plant are composed of large axial cells stacked on top of each other. Where these cells meet is called a node. At each of the nodes, additional cells are created, called periaxial cells. Each of the periaxial cells divides to form more cells, called cortical cells. Eventually, a cortex forms around each node of the plant. In some species, these cortical cells extend all the way up and down to the next node, fully covering the plant with cortex. In other species, the cortex may only be located directly around each of the nodes.

Drawing of C. californicum showing cortication Cortex of C. codicola close-up

Drawing of partially corticated C. californicum and close-up photo of fully corticated C. codicola.

Drawing of cross-section through node "Photo of cross-section through node"

Cross section through node, drawing and photo.

Ceramium is distinguished from the closely related genera Corallophila and Centroceras by the cortex cells: if the cortex cells are randomly arranged the alga is Ceramium. In both Corallophila and Centroceras, cortical cells are aligned in neat rows.

Cortex of Corallophila eatonianaCortex of Ceramium codicola

Cortication in Corallophila eatoniana (left) and Ceramium codicola (right).

Maggs et al. (2002) found that when cultured in a lab, the amount of cortication varied between plants of the same species, showing that degree of cortication might not be as useful a technique for determining species relationships as previously thought.


Filament apices
One of the other initial observations you might have after finding a piece of Ceramium in the field is the alga’s curved filament apices. In some species they lo

247>ok like crab claws (“forcipate” to the algal taxonomer) while in others they may look like little loops, and in others still apices might not be curved. Additionally, small branches coming off the main, larger branches of the plant (“adventitious branches”) may not show this forcipate structure. Apices of the plant are uniaxial, meaning topped with only one cell, and contain the meristematic regions where growth occurs.

Forcipate apices of C. codicolaForcipate apices of C. codicola

Forcipate apices in C. codicola with yellow-brown colored diatoms.


Rhyzoids
At the base of the alga, rhyzoids bind the plant to the substrate. In epiphytic species (algae that live on other algae), such as Ceramium codicola, these rhyzoids penetrate the anchor species, Codium, ensuring that the Ceramium will not be ripped from the anchor species in heavy wave action. In C. codicola, rhyzoids are bulbous at the tips, with thin strands of pigment in them.

Rhyzoids of C. codicola

Lightly pigmented rhyzoids of C. codicola, embedded in its anchor, Codium fragile.

© 2005 Lynn Asbeck

Last updated: Feb. 05, 2009