1. Chlorophyta
(i) Green algae are found all over the world. They combine with fungi to form lichens.
(ii) Algae of the class Charales are considered to be close relatives of higher plants.
(iii) Their pigments are chlorophyll a, b and carotenoids.
(iv) Their stored food is starch.
(v) Their cell wall is composed of cellulose and pectin.
(vi) Number of green algae is 7000.
Some green algae- Ulothrix zonata, Chlorella vulgaris, Spirogyra maxima, Volvox globator etc.
2. Diatom algae
(i) Diatom algae are golden-yellow in color. A complete diatom cell is called a frustule.
(ii) Their cell walls are strong, robust, composed of silica and richly ornamented bilayers.
(iii) They are called the ornaments of the sea or the living spectrum stones as they look very beautiful.
(iv) Dinoflagellate algae produce light in the darkness of night. The phenomenon is called bioluminescence (Noctiluca sp.).
(v) They have 10,000 species in 200 genera.
Some diatoms- Fragilaria capucina, Asterionella formosa, Tabellaria fenestrata, Navicula fossa, Noctiluca miliaris etc.
3. Phaeophyta
(i) Brown algae appear brown or yellow-brown in color because they contain fucoxanthin pigment.
(ii) Macrocystis is a large kelp algae. It forms underwater kelp forests. Its length is 60 meters.
(iii) The region of Atlantic Ocean where Sargassum algae grows in abundance is called Sargasso Sea.
(iv) Many brown algae grow on seashore rocks.
(v) Antioxidants in brown algae are anti-cancer and enhance the human immune system.
(vi) Brown algae species number 2000.
Some brown algae- Macrocystis pyrifera, Sargassum muticum, Ascophyllum nodosum, Laminaria digitata, Fucus elastica etc.
4. Rhodophyta
(i) Red algae appear red due to the presence of r-phycoerythrin pigment. These are called marine mosses.
(ii) Red algae that form coral reefs are called coralline algae. They excrete calcium carbonate to form coral reefs.
(iii) Red algae increase the body’s immune system by producing white blood cells.
(iv) Nori in Japan, Jim in Korea and Laver in UK are made from Porphyra algae.
(v) They are a large group of marine algae with over 7000 species.
Some red algae- Corallina elongata, Bangia fuscopurpurea, Stylonema alsidii, Polysiphonia lanosa etc.