Xanthophyceae

Tribonema sp. Photo by:Entwisel et al./ Botanic Gardens Trust.

Classification

Higher order taxa:

Eukaryota; stramenopiles

Genera

Vaucheria, Tribonema, Botrydium

Description and Significance

Commonly called the yellow-green algae. There are about 600 species of Xanthophyceae, all but three (Botrydium, Tribonema and Vaucheria) of the species are very rare. Before 1899 there were so few species known that they were categorized with the Chlorophyta. The two main varieties are found as large green vesicles up to several mm in diameter. They are often confused with green algae because it is pigmented by chlorophyll and lacks the fucoxanthin that is present in other Chyrsophyta.

Genome Structure

There has not been a genome project on Xanthophyceae yet, however there have been some experiments studying how the organism can morph to adapt to frigid waters. There is also evidence from DNA sequence comparison that Xanthophyceae is genetically related to Raphidophyceae (click here for abstract on research.)

Cell Structure and Metabolism

File:Reproduction Vaucheria.gif

Diagram of life cycle. Sexual reproduction on left, asexually on right.
Photo by:Ivy Linginstone/ Biodiac

Xanthophyceae are a photosynthetic group of yellow-green algae. Their photosynthate is stored as oils and the storage polymer chrysolaminarin. Most Xanthophyta are coccoid or filamentous, but some are siphonous, meaning that they are composed of multiple tubular cells with several nuclei. What makes up the cell wall is unknown but inside some there are two silica valves similar to those in diatoms. For the species that are filamentous the interlocking halves are in the shape of a H.

While not much is known about the life cycle of xathnophyta generally their reproduction is asexual, in which the cell divides bilaterally and creates and produces an endogenous cyst. Reproduction has only been observed in two xanothophtyes: in Vaucheria, it was found to be oogamous, and Botrydium reproduces by means of bimastigote zoospores or aplanospores.

Ecology

Xanthophyta are generally found in freshwater, wet soil and tree trunks, but there are several marine species. Most of the species occur singly and are found around other algae, making it difficult to find the same species twice. They do very well at low pH in habitats that are rich in iron. It was also found that Xanthophyceae loses its cytoplasmic streaming ability and organization of other vegetative filaments, when it is in an aluminum-rich environment. Many of them are found in late winter among floating mats in still water.

The species Vaucheria longicaulis has a unique characteristic in that it will send a larvae of Alderua modesta into spontaneous metamorphorosis when the larvae comes in contact with it. The adults can create two kinds of larvae, planktotrophic or lecithotrophic. Lecithotrophic clutches contain a mix of larvae, some which settle spontaneously, and others that need to be exposed to Vaucheria longicaulis.There were other experiments done to test and see if other algae would have the same effect and out of the 17 none did except for Vaucheria longicaulis.

[[Image:Botrydium_bubbles.jpgBotrydium granulatum. Photo by: Bioimages]]