In this article we will discuss about the external morphology of polysiphonia.
1. Plant body is bush like (Figs. 47, 48) and red or dark blue-coloured.
2. It is multiaxial in habit and few centimeters to several inches in length.
3. Prostrate part of the thallus is attached to the substratum with the help of many elongated and aseptate rhizoids. These rhizoids sometimes form the attachment disc (Fig. 47).
4. Upright filaments are laterally or dichotomously branched.
5. Upright or erect system consists of a main axis having long and short branches.
6. Plant body is made up of many siphons.
7. Each Long Branch and main axis consists of a central siphon made up of many elongated cells arranged one upon the other.
8. Central siphon is surrounded by many (4 to 20) pericentral siphons (Fig. 49).
9. Cells of the central and pericentral siphons are connected with each other by cytoplasmic connections or pit connections.
10. Short branches consist of cells arranged in a single row and so are unisiphonous. These are called trichoblasts.
11. Trichoblasts are present on main axis and long branches, and are dichotomously branched.
12. Each cell is uninucleate with many discoid chromatophores arranged peripherally in the cytoplasm. Cell wall is thick and each cell contains a large central vacuole. Cells lack pyrenoids (Fig. 49).