Karling, J. S.

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A Key to the Subgenera of SynchytriumJohn S. Karling, Purdue UniversitySy?ichytrium is the largest and most commonly known of the chytridia-ceous genera and includes at present nearly 200 reported species which areobligate parasites of algae, mosses, ferns and flowering plants. On thebasis of differences in life cycle and type of development the known speciesmay be grouped into seven subgenera as follows:A. Life cycle including sporangial sori and resting spores.1. Mature thallus functioning as a prosorus; contents emergingfrom initial cell of thallus to form a thin-walled sorus whichcleaves into sporangia.a. Resting spore functioning as a prosorus in germination;contents emerging to form a thin-walled sorus which cleavesinto sporangia.Subgenus Microsynchytriumb. Resting spore functioning as a sporangium in germinationand giving rise directly to zoospores.Subgenus Mesochytrium2. Mature thallus functioning directly as a sorus of thin-walledsporangia; sporangia delimited by cleavage within the soruswall and freed by its rupture.a. Resting spore functioning as a sporangium in germinationand giving rise directly to zoospores.Subgenus Eusynchytriumb. Resting spore functioning as a prosorus in germination;content emerging to form a thin-walled sorus which cleavesinto sporangia.Subgenus ExosynchytriumB. Life cycle including only sporangial sori, or resting spores.1. Only sporangial sori known.a. Mature thallus functioning directly as a sorus of thin-walled sporangia; sporangia delimited by cleavage withinthe sorus wall; freed by its rupture, and appearing aspowdery masses in open aecidium-like pustules.Subgenus Woroninella2. Only resting spores known.a. Resting spore functioning as a prosorus in germination.Subgenus Pycnochytriumb. Resting spore functioning directly as a sorus in germi-nation.Subgenus EndosynchytriumThis key varies to some extent from the one proposed by the authorin 1953, in that the subgenera of species with the long and more complexlife cycles are placed first. This position is based on the working hypoth-248Taxonomy 249esis, proposed by the author (1954), that the complex aquatic speciesmight be the most primitive, and that as species began to parasitize ter-restrial plants the life cycles became less complex and shorter. It isequally plausible, on the other hand, that the short-cycled species mightbe the most primitive, and through them have evolved the most complexspecies of Synchytrium.Literature CitedKarling, J. S. 1953. Micromyces and Synchytrium. Mycologia 45 : 276-287.——. 1954. Possible Relationships and Phylogeny of Synchytrium. Bull.Torrey Bot. Club 81 : 353-362.

A key to the subgenera of Synchytrium

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A key to the subgenera of Synchytrium

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