Phaeophyceae

Phaeophyceae are brown colour algae that live mostly in cooler seas.

Characteristics of phaeophyceae are following

(i) Mostly marine, only a few are fresh water.

(ii) All species are multicellular; the plants may exhibit complex morphology with highly differentiated tissue.

(iii) Flagella laterally inserted, heterokont with one anterior longer tinsel and another posterior shorter, whiplash, flagellate cells are always reproductive, no free living flagellate.

(iv) Flagellate cells have typical heterokont photoreceptors at the base of smooth flagellum and have adjoining eyespot inside the cells within the chloroplasts.

(v) Transition region of flagellum is lack of transition helix.

(vi) Chloroplasts are may be discoid.

(vii) Chloroplasts are having two membranes of chloroplast endoplasmic reticulum, thylakoid grouped into stacks of three, girdle lamella present.

(viii) Photosynthetic pigments are chlorophyll a, chlorophyll c1, chlorophyll c2, fucoxanthine.

(ix) Additional xanthophylls: violaxanthin, antheraxthine, neo xanthine, diadioxanthin, diatoxanthine, beta carotenes may be present.

(x) Mitosis are of semi closed.

(xi) Cell wall composed of felt like network of cellulose microfibrils, calcium alginate, amorphous fucoxanthine and mucilaginous alginate causes stiffening of the cell wall.

(xii) Sexual reproduction iso, aniso, to oogamous.

(xiii) Gametes are produced in plurilocular gametangia.

(xiv)Meiospores are produced in until ocular sporangia.

(xv) Life cycle diplobiontic or haplobiontic diploid type.

(xvi) In case of later meiosis is gametic.

(xvii) Sex hormone in Phaeophyceae - sex hormone in phaeophyceae are pheromones like diffusible substances (sirenine). This substances cause explosive discharge of male gametes from antheridia. Sex hormones of phaeophyceae are unsaturated hydrocarbons which are highly volatile in nature and hydrophobic by its nature. So, they help female gametes to attract male gametes towards female gametes. Examples of some sex hormones are – lamoxirene from Laminaria etc.

Laminaria, Sargassum are edible algae.

Phaeophyceae can be divided into different order. They are following-

1. Ectocarpales

2. Sphacelariales

3. Cutleriales

4. Laminariales

5. Fucales

6. Dictyotales

Questions and answers on Phaeophyceae:

1. What is photosynthetic reserve in phaeophyceae?

Laminarin.

2. How are brown algae related to ozone hole?

Like man made halogenated compounds, CFC (chlorophyll fluro carbon), brown algae are known to release large quantities of volatile brominated methanes into the environment. It is suspected to be responsible for ozone destruction in the atmosphere above the Arctic as the annual global input of the algal organobromides has been estimated at ca 10000 tonnes per year. Arctic is dominated by gigantic seaweed.

3. What do you mean by sirenine?

Sex hormones of phaeophyceae are called sirenine.

4. Name a member of phaeophyceae where encrustation of calcium carbonate is observed.

Padina.

5. What do you know about kelps?

Members of Laminariales are called kelps. The term is also applied to burn ash of Laminariales. Kelps are characterised by large sporophytic thallus differentiated into holdfasts, stipe, blade regions with an intercalary meristem located at the junction of the stipe and blade.

6. Where do you find phase change in Phaeophyceae?

Phase change is an unusual phenomenon noticed in certain Phaeophyceae where two morphologically different thallus types occur in the same number not always associated with sexual reproduction or change in chromosomal level. E.g. the same taxon known under two generic names Feldmannia and Acinetospora actually represents different ecological manifestations under different climatic conditions. Acinetospora forms in cold season where as Feldmannia occurs in warm season.

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