The following points highlight the nine main characteristics of Xanthophyceae.
1. Members of Xanthophyceae are commonly fresh water (Tribonema) and most of them are free floating. [Few members are found to grow on mud (Botrydium) and also on walls or tree trunks (Characiopsis, Ophiocytium etc.). A few members like Halosphaera are marine.
2. Plant body is unicellular (Heterochloris) or multicellular. [The multicellular bodies also exhibit various forms like palmelloid (Chlorogloea), dendroid (Mischococcus), coccoid (Chlorobotrys), rhizopodial (Stipitococcus), filamentous (Heterococcus) and siphona- ceous (Botrydium).
3. The cell wall is often absent, but when present it contains more pectic compounds than the members of Chlorophyceae. Occasionally cellulose is also present. [In some non- motile forms the cell wall is silicified and made up of two halves, those overlap each other.
4. The motile forms bear usually two flagella but rarely one. They are unequal and inserted at the anterior end. The flagella are of two types. The larger one is tinsel (or pantonematic or pleuronematic i.e., bearing halr-like appendages) and the shorter one is whiplash (or acronematic i.e., without hairs and their surface is smooth) type.
5. The chromatophores are discoid in shape and are numerous in each cell.
6. The pyrenoides are absent or rarely present.
7. The plastids are yellow-green in colour. The photosynthetic pigments are chlorophyll a, chlorophyll e (very little), P-carotene (fairly high concentration) and xanthophylls. The chief xanthophyll is diadinoxanthin. The other xanthophylis are violaxanthin, lutein, neoxanthin, flavoxanthin and flavacin. The carotenoides are normally present in excess amount than chlorophyll. Chlorophyll b is absent.
8. The reserve food is oil, lipid and lucosin. Starch is not formed.
9. Plants reproduce commonly by vegetative and asexual means. Vegetative reproduction takes place by cell division. Asexual reproduction by zoospores, aplanospores or akinetes. Sexual reproduction, though rare, may be isogamous, anisogamous or oogamous. Isogamy is common. Both iso- and anisogamy are found in Botrydium.
