Cytological and cytochemical aspects in selected carrageenophytes (Gigartinales , Rhodophyta)

Red algae (Rhodophyta) are a widespread group of uni- to multicellular aquatic photoautotrophic plants. They exhibit a broad range of morphologies, simple anatomy and display a wide array of life cycles. About 98% of the species are marine, 2% freshwater and a few rare terrestrial/sub-aerial representatives (Gurgel and Lopez 2007). Red algae are true plants in the phylogenetic sense since they share, with the green lineage (green alga e and higher plants), a single common ancestor (Adl et al. 2005). However, the phylum Rhodophyta is easily distinguished from other groups of eukaryotic algae due to a number of features listed below (Woelkerling 1990; Grossman et al. 1993; Gurgel and Lopez 2007):

(i) Total absence of centrioles and any fl agellate phase.

(ii) Presence of chlorophyll s a and d , and accessory pigments (light-harvest) called phycobilin s (phycoerythrin and phycocyanin).

(iii) Plastid s with unstacked thylakoid s, and no external endoplasmic reticulum.

(iv) Absence of parenchyma and presence of pit-connection s between cells (i.e. incomplete cytokinesis).

(v) Floridean starch as storage product.

Traditionally, red algae can be morphologically separated in three major groups: (1) a unicellular group with reproduction by binary cell division only, (2) a multicellular group where a carpogonial branch is absent or incipient (Bangiophyceae sensu lato) and (3) a multicellular group with well developed carpogonial branches (Florideophyceae).