Important orders in the Phaeophyceae class as formulated by Dr. F.E. Fritsch are as follows:
According to Dr. F.E. Fritsch, there are nine orders in this class:
1. Ectocarpales, 2. Tilopteridales 3. Cutleriales, 4. Sporochnales, 5. Desmarestiales, 6. Laminariales 7. Sphacelariales, 8. Dictyotales, 9. Fucales.
The outline of Taylor’s system is as follows. About 12 orders are included in this sytstem. The whole class is divided into three sub-classes.
Three sub-classes are:
I. Isogeneratae. Isomorphic alternation of generations.
II. Heterogeneratae. Heteromorphic alternation of genemaions.
III. Cylosporeae. Diplontic type of life cycle.
The sub-class Isogeneratae includes 5 orders.
Branched heterotrichous filamentous body; trichothallic growth; reproductive bodies terminal or intercalary, single or in chain; the sporophyte produces zoospores or neutral spors (2n); isogamy.
Growth by single large apical cell segments formed which frequently divide lengthwise in a regular polysiphonous manner; sporophyte may produce haploid or diploid zoospores; iso or anisogamy.
Thallus freely branched showing trichothallic growth, upper portion monosiphonous; lower portion polysiphonous; sporophytes produce unilocular sporangia only, each containing a single quadrinucleate aplanospore; gametangia are intercalary; doubtful oogamy.
Thallus flattened, blade-like or disc-like, dichotomously branched, trichothallic growth; the sporophyte produces unilocular sporangia only; anisogamy.
Erect flattened dichotomously branched parenchymatous thallus; growth by a single apical cell or a marginal row of special cells; the unicellular sporangia of sporophyte each produces 4 or 8 aplanospores; oogamy.
The sub-class Heterogeneratae includes two series and six orders.
Series 1. Haplostichineae. Growth trichothallic; thallus consists of one or more filaments.
Series 2. Polystichineae. Trichothallic growth absent; longitudinal and transverse intercalary cells form a parenchyma.
Three orders are included in Series Haplostichineae.
Branched filamentous sporophyte; isogamous.
Each branch of the sporophyte terminates in a tuft of hairs; growth is trichothallic due to intercalary cell division at the base of each hair; the unicellular sporangia are borne terminally in dense clusters; plurilocular sporangia absent; oogamy.
The thallus has a single filament of each growing apex posterior to which there is pseudoparenchymatous cortication, the thallus is macroscopic; oogamy, gametophyte microscopic.
Three orders are included in Series Polystichineae.
Parenchymatous, sporophyte of medium size; reproductive organs may or may not be borne in sori; the sporophyte reproduces by zoospores; iso or Anisogamy. gametophyte microscopic.
Profusely branched cylindrical thallus, growth by single apical cells; sporophyte produces unilocular sporangia only; isogamy, gametophyte microscopic.
Sporophyte differentiated into a holdfast stipe, and blades; growth by intercalary meristem; internal structure of thallus is differentiated into epidermis, cortex and medulla, the medulla shows ‘trumpet hyphae’ with callus pads; oogamy, gametophyte microscopic; the sporophyte bears only unicellular sporangia in sori.
The sub-class Cyclosporeae includes a single order Fucales.
Life cycle is diplontic; growth by single apical cell, thallus parenchymatous; unilocular sporangia borne in conceptacles; the egg is liberated in the water prior to fusion.