Classification of Rhodophyta | Algae

In this article we will discuss about the classification of rhodophyta.

The presently accepted classification of the Rhodophyta having the single class Rhodophyceae is the system first devised by Schmitz (1883) and refined through years of painstaking work by Kylin (1932) and others to a form finally adopted and presented by Kylin in his monograph of 1956.

Modifications have been made in this system in recent years and continue to be made as life histories are worked out and new relation­ships of the reproductive phases are recognized. On the other hand, some authors consider the system inadequate, unstable, and in need of complete revi­sion.

The following is an outline of the distinctive characters of the classification of the class Rhodophyceae presently recognized by a majority of phycologists:

1. Cells with cytoplasmic connections; cell division rarely intercalary; carpo- spores produced in carposporangia borne on gonimoblast ilaments…3 Subclass: Florideophycidae

3. Life history usually without a free-living tetrasporophyte, or, if such pre­sent, then sexual and sporophytic generations usually heteromorphic

Order Nemalionale:

3. Life history usually with free-living tetrasporophyte; sexual and sporo­phytic generations isomorphic… 4

4. Gonimoblasts growing directly from a carpogonium fusion cell Order Gelidiales

4. Gonimoblasts growing mostly from an auxiliary cell… 5

5. Auxiliary cell an intercalary vegetative cell Order Gigartinales

5. Auxiliary cell not an intercalary vegetative cell

6. The auxiliary cell formed before fertilizatio… 7

6. The auxiliary cell formed after fertilization and cut off directly supporting cell of carpogonial filament Order Ceramiales

7. Auxiliary cell in a special filament and usually not borne on the supporting cell of the carpogonial filament Order Cryptonemiales

7. Auxiliary cell the terminal cell of a usually two-celled filament borne on the supporting cell of the carpogonial filament

Order Rhodymeniales:

1. Cells usually without cytoplasmic connections; cell division intercalary; carpospores formed by direct division of the zygote

Subclass Bangiophycidae

2. Spore formation usually preceded by cell division; sexual reproduction present in most genera

Order Bangiales

2. Asexual reproduction only by monospores without cell division; sexual reproduction unknown

Order Goniotrichales

The Glass Rhodophyceae is also conveniently divided as follows:

Subclass Florideae:

Well-developed thalli of filamentous branched to pseudo­parenchymatous forms; growth of the thallus by apical cell; pit-connections invariably present between the cells; sex organs highly differentiated; carposporangia developing on filamentous gonimoblasts derived directly or indirectly from the zygote; meiosis immediately after the formation of diploid nucleus or delayed; chiefly marine. Include six orders.

Order Nemalionales:

Plant body heterotrichous with uni- or multi-axial cons­truction; cells with a single chromatophore; asexual reproduction by monospores or tetraspores; male and female gametophytes present; sporophyte represented by zygote (fertilized carpogonial nucleus); zygotic meiosis; the fertilized carpogonium giving rise to branches which form the gonimoblasts; carposporangia are haploid and bear hap­loid carpospores; usually marine, but a few forms are fresh-water.

Family: Batrachospermaceae:

Soft, thick, gelatinous branched thallus being differentiated into structures resembling nodes and internodes; branches arise in whorls from the nodes; reproduction by monospores, carpogonia and spermatangia; fertilized carpogonial nucleus divides reductionally producing short gonimoblast filaments from which carposporangia and haploid carpospores are developed.

Genus:

Batrachospermum

Order Gelidiales:

Small order with only a few genera in two families, but some of the species common and very widely distributed, some of considerable economic importance; show an alternation of portion of sporophyte and gametophyte plants; sexual plants dioecious and distinguishable only when fertile; most members of the order plants of moderate size, of firm, cartilaginous consistency, of uniaxial construc­tion, and of monopodial branching, carpogonial filaments single-celled and deeply embedded in the cortex of very young thallus parts; gonimoblasts developing directly from a multinucleate fusion cell formed from the carpogonium alone or as a result of the fusion of the carpogonium and certain neighbouring cells.

Order Gigartinales:

Diversified having an assemblage of algae as the Grypto- nemiales, but, with few exceptions, the members being fleshy and non-calcarious forms; plants of monoaxial or multiaxial construction and of cylindrical to foliaceous forms; only a few prostrate or crustose, and none filamentous or microscopic.

According to Kylin’s system, the order is technically distinguished by the auxiliary cell being an intercalary vegetative cell and not a cell borne in a special filament. It should be pointed out, however, that in some Gigartinales the supporting cell may function as an auxiliary cell and that this presents a seeming contradiction. A parallel situation obtains in the Cryptonemiales and makes these ordinal distinctions extremely obscure.

Order Ceramiales:

Uni- to multi-axial construction of thallus; male and female gametophytes alternating with sporophyte; sporophyte producing tetrasporangia and tetraspores; carpogonial branch with procarp; presence of auxiliary cells being cut off from the basal cell of the carpogonial branch after fertilization; diploid carpospores; meiosis during tetraspore development.

Family: Ceramiaceae:

Thallus formed of monosiphonous filaments, naked or corticated by secondary filaments developed at the nodes and adhering to the main axis; pro-carp exterior to the thallus; cystocarp often formed of gonimoblast; tetrasporangia usually tetrahedral and exterior. Genera: Ceramium, Callithamnion.

Family: Rhodomelaceae:

Polysiphonous thallus with basal filaments attached to the substrate by small flattened disks; laterally or dichotomously, branched thallus; spermatangia and procarps developed exterior to the main axis; cystocarps urn-shaped with a pore, usually shortly pedi­cellate; tetrasporangia with tetra-spores.

Genus:

Polysiphonia.

Order Cryptonemiales:

Diversified in forms, structure, and substance than any other group; gelatinous, fleshy, cartilaginous, and calcareous types in remarkable array; all of these having the auxiliary cell formed before fertilization and borne on a special filament of the gametophyte, the auxiliary cell filament usually resembling the carpogonial filament in its dense cytoplasm and may be distinguished before ferti­lization, it may be borne far removed from the carpogonial filament, or both may arise from a common cell.

Order Rhodymeniales:

Characteristic multiaxial growth of thallus; a three- or four-celled carpogonial branch; the presence of a procarp with one or occasionally two auxiliary cells not part of the vegetative system; auxiliary cell branch (produced by the supporting cell usually composed of two cells) initiated before fertilization; the mature tetrasporangia either cruciately or tetrahedrally divided; the life cycle almost always diplobiontic.

Family: Champiaceae:

Most of the thallus, or at least the reproductive part hollow and with longitudinal filaments bordering the cavity; tetra­sporangia generally tetrahedrally divided, but some genera with poly- sporangia.

Family: Rhodymeniaceae:

Thallus solid or hollow, but if hollow, longitudinal filaments lacking; tetrasporangia generally cruciate divided.

Subclass Bangioideae:

Simple thallus with diffuse growth never exhibiting aggregation of filaments; pit-connections between cells of the thallus lacking; plants either entirely asexual or consisting of monoecious or dioecious gametophytes; the zygote representing the sporophyte; sex organs little specialized; carposporangia formed by direct division of the zygote; terrestrial, fresh-water, and marine. Include one order.

Order Bangiales:

Cells forming the thallus isolated or united into filamentous or membranous colonies, of one or two cell layers; cells usually similar in form, with intercalary growth, obvious cytoplasmic continuity never established; red, violet, yellowish or occasionally bluish-green; plastids usually stellate.

Vegetative reproduc­tion by cell division in unicellular forms, by fragmentation in multicellular forms; asexual reproduction by non-motile spores, produced in an undivided vegetative cell or in a portion cut off by a curved wall; sexual reproduction by spermatangia and carpogonia, formed in the cells of the thallus; monoecious or dioecious, fertilization resulting in the producing of carpospores.

Family: Erythrotrichiaceae:

Plant body filamentous branched or un-branched or laminate to cylindrical thalloid structure; reproduction by the deve­lopment of large and small spores formed by the division of vegetative cells.

Genus:

Compsopogon.

Order Goniotrichales:

Microscopic, epiphytic representative of this order common; it occurs on a wide variety of hosts and almost cosmopolitan; readily recog­nizable by its branched filaments of seriate cells with very thick, gelatinous walls; only the simplest kind of asexual reproduction known; the vegetative cells directly transformed into monospores freed by dissolution or rupture of the adjoining gelati­nous walls.