CLASS ULVOPHYCEAE

Most are marine, but some occur in abundance in freshwater habitats. These range from uninucleate to multinucleate filaments to siphonaceous forms to giant unicells. The green seaweeds, most of which are diploid in the vegetative state, belong to this class. Basal bodies are cruciate and occur in a counterclockwise displacement. However, there seem to be no real synapomorphies for this class. Thus, van den Hoek (1995) advocated raising the subgroups to class status. I have taken a more conservative stance. This class has 6 orders.

• ORDER ULOTRICHALES (contains taxa of orders Ulotrichales and Codiolales from older systems).
  • Filaments of uninucleate to multinucleate cells. Some a sheet of a single layer of uninucleate cells. Commonly, members of this order have a stage of their life history that is unicellular, club-shaped, attached and stalked (this usually is assumed to be the zygote).
  • Ulothrix, Urospora, Spongomorpha, Acrosiphonia, Monostroma, Geminella, Stichococcus, Cylindrocapsa.

• ORDER ULVALES
  • Parenchymatous; often a flat expanded sheet, hollow tube or solid cylinder; asexual reproduction by flagellated zoospores; sexual life history isomorphic alternation of generation with biflagellate gametes.
  • Ulva, Enteromorpha, Percursaria, Ulvaria, Trichosarcina, Prasiola.

• ORDER TRENTEPOHLIALES = CHROOLEPIDACEAE
  • These branching filaments differ from the CHAETOPHORALES because the TRENTEPOHLIALES produce specialized gametangia and zoosporangia. Terrestrial or parasites of plants. Some are the phycobionts of lichens.
  • Trentepohlia, Cephaleuros.

• ORDER SIPHONOCLADALES = CLADOPHORALES
  • Branched filaments, pseudoparenchymatous blades, nets or spherical vessicles; always of multinucleate cells; reproduction by flagellated zoospores and gametes; alternation of haploid gametophyte and diploid sporophyte generations; cell walls thick and rough.
  • Cladophora, Rhizoclonium, Chaetomorpha, Pithophora, Basicladia, Anadiomene, Siphonocladus, Dictyosphaeria, Valonia, Sphaeroplea.

• ORDER CAULERPALES = BRYOPSIALES
  • Branched siphonaceous organization, some multiaxial or pseudoparenchymatous; diploid with alternation of haploid and diploid generations with flagellated gametes or diploid with gametic meiosis and oogamy.
  • Bryopsis, Pseudobryopsis, Derbesia, Caulerpa, Udotea, Codium, Halimeda, Penicillus, Dichotomosiphon.

• ORDER ACETABULARIALES = DASYCLADALES
  • Thallus complex with radial symmetry, sometimes bladder-like or umbrella-like; cell wall of cellulose but may become calcified; diploid with gametic meiosis.
  • Acetabularia, Batophora, Cymopolia.

CLASS CHLOROPHYCEAE

There are two subgroups of this class known as the DO (directly opposed basal bodies) clade and the CW (clockwise arrangement of basal bodies) clade. Flagella non-scaly; flagellar roots run in periphery of cell; usually haploid, but alternation of haploid and diploid generations in some; morphology varied. This class has 5 orders.

• ORDER SPHAEROPLEALES (DO Clade)
  • These range from unicells to coenobial colonies to multinucleate filaments (Sphaeroplea). Some do not produce motile cells (and therefore cannot be confirmed as DO) but are related to other taxa as confirmed by molecular phylogeny.
  • Ankistrodesmus, Bracteacoccus, Pediastrum, Hydrodictyon, Scenedesmus, Coelastrum, Tetraedron, Sphaeroplea

• ORDER VOLVOCALES (CW Clade)
  • This is a large, diverse group that seems to have 3 well-defined clades:
  • 1. The volvocine clade: Vegetative stages flagellated or coenobia; some non-flagellated pallemloid colonial forms whose vegetative cells have pseudocilia (9+1); gametes and zoospores normally biflagellate. (formerly the orders Volvocales and Tetrasporales)
  • Volvox, Chlamydomonas (some), Dysmorphococcus, Carteria, Chlorogonium, Polytoma, Haematococcus, Phacotus, Pteromonas, Gonium, Pandorina, Platydorina, Pleodorina, Eudorina;: Tetraspora, Gloeococcus, Palmella, Gloeocystis, Hormotila, Paulschulzia, Apiocystis.
  • 2. The tetracystis clade: This group includes some unicellular non-motile forms formerly in the order Chlorococcales.
  • Chlorococcum (some), Tetracystis.
  • 3. The dunaliella clade: This contains some of the Chlamydomonas species (now recognized as a paraphyletic genus), some nonmotile coccoid taxa (some species of Chlorococcum), and some coenocytic taxa.
  • Haematococcus, Chlamydomonas (some), Stephanosphaera, Dunaliella, Chlorococcum (some), Botryococcus, Oocystis, Planktosphaeria, Micractinium, Kirchneriella, Sphaerocystis, Dictyosphaerium, Dimorphococcus, Selenastrum, Protosiphon, Characiosiphon.

• ORDER CHLOROSARCINALES
  • Unicellular green algae which can undergo vegetative cell division (as well as the production of zoospores); soil algae.
  • Chlorosarcina, Pseudotetracystis, Borodinellopsis, Borodinella, Axilosphaera, Planophila.

• ORDER CHAETOPHORALES
  • Branched filaments; long hairs or setae at the ends of some cells; biflagellate zoospores and gametes.
  • Chaetophora, Uronema, Microspora, Stigeoclonium, Draparnaldia, Draparnaldiopsis, Fritschiella, Microthamnion, Protoderma, Gongrosira, Aphanothece.

• ORDER OEDOGONIALES
  • Filamentous; cells uninucleate and have complex method of cell division (cell cap formation); haploid with zygotic meiosis; oogamous; flagellated zoospores and sperm bear ring of numerous flagella.
  • Oedogonium, Bulbochaete, Oedocladium.

CLASS TREBUXIOPHYCEAE = PLEURASTROPHYCEAE

Centrioles position themselves at the sides of the spindle in these taxa. This is called metacentric mitosis and is considered to be a derived state from mitosis with polar centrioles. These range from unicells to small filaments and sheets of cells. Many of these occur as the phycobionts in lichens. Sexual reproduction is equally varied. Basal bodies in a counterclockwise displacement. (from Friedl 1995; Graham and Wilcox 2000; and Van den Hoek et al. 1995).

• ORDER TREBUXIALES.
  • Myrmecia, Trebouxia, Dictyochloropsis, Chlorella, Nanochlorum, Prototheca, Stichococcus, Golenkinia, Eremosphaera, Microthamnion.