General Characteristics of Xanthophyta
The members of this division are characterized by their yellow-green color. So, the members of this division are called yellow-green algae. The division includes 76 genera and 376 Species which are included in a single class, the Xanthophyceae.
Characteristics of Xanthophyta
- A majority of yellow-green algae are freshwater but some of the species are aerial growing on tree trunks, on damp walls or soil on drying mud. A few species are marine e.g., Halosphaera.
- The members of the class show a wide range in thallus structure. The thalli range from unicell (Chloramoeba, Choromeson) to palmelloid state (Chlorosaccus), and also through the filamentous (Tribonerna, Heterococcus) to the siphonaceous habit (Vauchena, Botrydium).
- The xanthophycean cell has a definite cell wall chiefly composed of pectic substances either pectose or pectic acid. In many genera, the cell walls are in the form of two equal or unequal overlapping halves.
- The cells in motile genera have two unequal flagella attached to the anterior end. One flagellum is tinsel type and the other whiplash type.
- The pigments are located in discoid chromatophores and consists of chlorophyll- a, chlorophyll-e, beta-carotene and xanthophylls. Chlorophyll-b is absent. The dominant pigment is a xanthophyll diadinoxanthin which provides the cells its characteristics yellow-green color. The pyrenoids are absent.
- The chief reserve foods are oil, lipid and leucosin (chrysolaminarin). Many genera have uninucleate cells while others have multinucleate ones.
- The members of the class usually reproduce vegetatively and asexually, but in few genera sexual reproduction is also found.
- The asexual reproduction may be by zoospores, aplanospores and akinetes.
- The sexual reproduction is rare and is generally of isogamous type found among the siphonaceous genera like Vaucheria.