Salient features of Rhodophyta

Division - Rhodophyta:-

Salient Features:-

> Red Algae are an ancient group of algae with over 5,000 living species.

> Majority of them are marine. A few (example- Batrachospermum, Lemnaea) are freshwater aquatic or subaquatic terrestrial (example- Porphyridium).

> Their size varies from unicellular microscopic forms to half a metre in length. Several species of red algae are graceful and lace-like plants. Some red algae secrete CaCO3 on their walls and form coralline algae.

> They are red in colour due to phycoerythrin and phycocyanin pigments. They have chlorophyll a molecule to capture the blue-green sunlight.

> These are photo-autotrophic, but some others are colourless, lack photosynthetic pigments and live as parasites on other photosynthetic red algae (Example- Harveyella).

> Reserve food is in the form of floridean starch and a soluble starch, floridoside.

> Flagellate forms and stages are completely absent.

> Cell Wall consists of cellulose and pectic compounds. Sulphated geloses or phycocolloids occur in most red algae. The important ones are agar, carrageenin and funori.

> Vegetative reproduction occurs by fragmentation, gemmae and regeneration of holdfast.

> Reproduction occurs by both sexual and asexual methods. The spores are non-motile. Sexual reproduction is highly specialised. Male gametes are non-motile and called spermatia. Spermatia are carried by water currents to elongated tip trichogyne of female sex organ carpogonium. Following fertilisation, the zygote may produce carpospores. Example- Poryphyra by division directly or indirectly from zygote as in Batrachospermum and Polysiphonia.

> The life cycle of many red algae like Polysiphonia has an alternation of haploid and diploid multicellular generations.

Classification:-

Class:- Rhodophyceae

3 Sub-classes:-

a. Porphyridae:-

Order:- Porphyridales

Eg.- Porphyridium

b. Bangidae:-

Order:- Bangiales

Eg.- Bangia, Porphyra

c. Floridae:-

i. Order:- Nemaliales

Eg.- Nemalion

ii. Order:- Ceramiales

Eg.- Ceramium, Polysiphonia, Batrachospermum