Aphanomyces phycophilus de Bary 1860

Aphanomyces phycophilus De Bary, Jahrb. Wiss. Bot
2: 179. 1859.
Hyphae larger than in other species of the genus, 7.4— 14 fx thick, growing longitudinally through the cells of Spirogyra or Zygnema and developing numerous, considerably branched haustoria which intermingle with the chromatophores, causing their disorganization and collapse into irregular masses; threads often extending outside the host; asexual reproduction not observed ; oogonia formed in considerable abundance, usually extramatrical but rarely also formed within the host-threads, borne on lateral stalks equal in length to or slightly longer than the diameter of the oogonia; oogonia 40-50 p. in diameter counting the numerous, conspicuous, blunt spines, the spines 6-9.3 y. long, the wall becoming dark-brown upon maturity; eggs single. 30-38 m thick; antheridia of diclinous or androgynous origin, usually one on an oogonium. (Description compiled from Couch, Jour. EHsha Mitchell Soc. 41: 214. 1926.)
Type locality: Germany.
Habitat: Obligate parasite on Spirogyra and Zygnema,
Distribution: New York, Michigan, Indiana, North Carolina, and South Carolina; also in Europe .