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 partially corticated C. californicum and
close-up photo of fully corticated C. codicola.
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.
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.
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 in C. codicola with
yellow-brown colored diatoms.
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.