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.
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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.
1. Ectocarpales:
Branched heterotrichous filamentous body; trichothallic growth; reproductive bodies terminal or intercalary, single or in chain; the sporophyte produces zoospores or neutral spors (2n); isogamy.
2. Sphacelariales:
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.
3. Tilopteridales:
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.
4. Cutleriales:
Thallus flattened, blade-like or disc-like, dichotomously branched, trichothallic growth; the sporophyte produces unilocular sporangia only; anisogamy.
5. Dictyotales:
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.
1. Chordariales:
Branched filamentous sporophyte; isogamous.
2. Sporochanles:
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.
3. Desmarestiales:
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.
1. Punctariales:
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.
2. Dictyosiphonales:
Profusely branched cylindrical thallus, growth by single apical cells; sporophyte produces unilocular sporangia only; isogamy, gametophyte microscopic.
3. Laminariales:
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.
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.