*Once an interaction has taken place between a carposporophytic cell and a vegetative cell, the fruiting body is called a cystocarp rather than a carposporophyte.

*The great diversity of cystocarp types ranging from simple to very complex has traditionally formed the basis for the classification of red algae (Kylin, 1956)

morphological approach

differentiation of morphological structure is described as function of filament ontogeny and cytological modification, and structures seen in different taxa are compared for similarities and differences at eachstate of development

Superficial morphological similarities may mask significant developmental differences that result in taxonomic confusion.

*Special staining & clearing techniques makes it possible to interpret the organization of complex structures & the rather obscure & ephemeral events of the sexual cycle.

*Without exceptions to date, molecular phylogenetic analyses seem to highlight the evolution of the earliest stages in the development of the female apparatus and associated cells.

*The molecular-based phylogenies each provide an independent test of classification to the one based on morphological or ultrastructural evidence.

*Besides elucidating relationships, phylogenetic hypotheses inferred from gene sequence data provide the critical framework for studies of morphological character evolution and life history evolution.

Major groups

*The Rhodophyta contains the monophyletic class Rhodophyceae & usually two subclasses, the paraphyletic Bangiophycidae & monophyletic Florideophycidae.

*The name Bangiophycidae continues to be used to identify the early diverging algae from which the Florideophycidae have evolved.

*The classification at the ordinal level is in a constant flux, & recent DNA sequencing studies have raised serious questions concerning the correctness of present systems of classification among the Rhodophyta & have led to proposals of new & recircumscribed orders.

*The Bangiophycidae are the ancestral pool from which the more morphologically complex taxa in the Florideophycidae have arisen, & they are the sources for the independent origins of the plastids, through secondary endosymbioses, for the Cryptophyta, Haptophyta & Heterokonta as inferred from DNA sequence comparisons (Oliveira & Bhattacharya 2000).

*They range from unicells to multicellular filaments (uniseriate or multiseriate, branched or unbranched) or sheet-like thalli (monostromatic or distromatic).

*Cells typically have a single axial stellate plastid with a large pyrenoid, though some taxa contain a cup-shaped plastid or a complex interconnected plastid lacking a pyrenoid (Gantt et al. 1986, Broadwater & Scott 1994).

*Pit connections are rare and sexual reproduction has not been described in many members of this subclass.

BangiophycidaePorphyra/Conchocelis

- biphasic, heteromorphic alternation of generations-dominant gametophyte: diffuse growth-species either mono-or distromatic. -sporophyte (conchocelis) creeping & small; unipolarspore germination; accompanied by change in plastid morphology & shift from production of xylan to cellulose in cell walls.

“nori”

BangiophycidaePorphyra/Conchocelis

Bangiophycidae Bangia

-uniaxial-pit plugs

Florideophycidae

*Cell walls of red algae consist of fibrillar part that gives wall its strength & amorphous part in which fibrils are embedded (=phycocolloids).

*most abundant of amorphous cell wall matrix that arecommercially exploited are galactans or polymers of galactose which are alternatively -1,3 and -1,4 linked agars & carrageenans

*agar composed of 2 polysacharides: agarose & agaropectin

*these mucilages may constitute up to 70% of dry weight of cell wall.

*phycolloid: insoluble in cold water but readily soluble in hot water with a 1% solution being clear & forming solid & elastic gel on cooling.

*in traditional processing procedure, plants are bleached in sun with several washings in freshwater; material is boiled for several hours & extract is acidified; extract then frozen & thawed.

*On thawing water flows from agar, carrying impurities with it & agar that remains is dried & marketed as flakes or cakes

*more modern method extracts agar under pressure in autoclaves: agar is decolorized & deodorized with activated charcoal, filtered under pressure & evaporated under reduced pressure. Further purification by freezing is then undertaken.

* non-toxic: used in food preparation and in pharmaceutical industry as gelling & thickening agent: canning of meat & fish & for protection against shaking in transit, manufacture of processed cheese, mayonnaise, puddings, creams, jellies

*Japan most important producer of agar, about 3500 tons annually

*used on large scale for preparation of gels: agar-agar: microbiological investigations: agar gels contain nutrients for bacteria & fungi but gel itself is resistant to degradation by these organisms

Florideophycidae Agarophytes Gelidium

Gelidiumuniaxial

Gelidium

Gelidium

Gelidium

cystocarp

AgarophytesGracilariopsis

vegetative structure:cellular medulla

young female reproductive system

earlycarposporophytestages

late carposporophyte stages: cystocarp

-superficial spermatangia-cruciate tetrasporangia

Dudresnaya-auxiliary cells & connecting filaments

CARRAGEENOPHYTE-multiaxial-medulla cellular + filiform-fusion cell type or placenta-zonate tetrasporangia

CarrageenophytesGigartinaceae

cystocarp

*Some taxa are parasitic on other red algal hosts.

*Morphological similarities of many parasites & their hosts have led to the speculation that some groups of red algal parasites may have developed directly from their hosts.

*These parasites, termed adelphoparasites may evolve monophyletically from one host and radiate secondarily to other hosts or, these parasites may arise polyphyletically, each arisingfrom its own host (Goff et al., 1996, 1997).