Phytomyxea

Phytomyxea
Resting spores of different species
Scientific classification
Domain:	Eukaryota
(unranked):	Rhizaria
Phylum:	Cercozoa
Subphylum:	Endomyxa
Class:	Phytomyxea Cavalier-Smith, 1993
Orders and Genera
Phagomyxida Phagomyxa Plasmodiophorida Cook, 1928 Lignieria Membranosorus Octomyxa Plasmodiophora Polymyxa Sorodiscus Sorosphaera Spongospora Tetramyxa Woronina
Synonyms
Phytomyxini Schröter, 1886:133 Phytomyxinae MacBride 1892:111; 1899:16; Schröter in Engler & Prantl, 1897; Doflein, 1911:672 Phytomyxinea Poche 1913:197 Phytomixida Calkins, 1926:328

The Phytomyxea are a class of protists that are parasites of plants. They are divided into the orders Plasmodiophorida (ICZN, or Plasmodiophoromycota, ICBN) and Phagomyxida. A more common name for them is the plasmodiophorids, but this does not always include Phagomyxa (see taxobox).

Life cycle

They typically develop within plant cells, causing the infected tissue to grow into a gall or scab. Important diseases caused by phytomyxeans include club root in cabbage and its relatives, and powdery scab in potatoes. These are caused by species of Plasmodiophora and Spongospora, respectively.

The vegetative form is a multinucleate cell, called a plasmodium. This ultimately divides to form new spores, which are released when the host's cells burst. Both resting spores and motile zoospores, which generally have two smooth flagella, are produced at different stages. Within the plasmodium, dividing nuclei have a distinctive cross-like appearance.

Classification

Plasmodiophorids are traditionally considered slime moulds, because of the plasmodial stage. Thus they are often classified as fungi, and given names such as the Plasmodiophoromycota. However, genetic and ultrastructural studies indicate they belong to a diverse group of protists called the Cercozoa, or are closely related to them.