The phylogenetic and taxonomic implications of flagellar rootlet morphology among zoosporic fungi.

Rootlet morphology shows that the Oomycetes excluding the Thraustochytriales, the Thraustochytriales independently, and the Hyphochytriomycetes probably evolved as three distinctive lines from chrysophycean ancestors. The Plasmodiophoromycetes rootlet system does not show any similarity to rootlet systems in other zoosporic fungi, and this class may have arisen from the Protozoa. The varied rootlet systems present in the Chytridiomycetes show that this class has a very primitive origin and long evolutionary history. The composition of the rootlet systems in different Chytridiomycete taxa indicate that the Monoblepharidiales evolved from the Chytridiales, and the Blastocladiales from the Spizellomycetales.