Studies on the Genus Phycomyces

Phycomyces belongs in the family Mucoraceae and asexually is more closely related to Mucor than to any other genus. It has globose sporangia containing many sporangiospores and typically Mucor-like columellae. The extremely long sporangiophores are similar to those of Mucor, except that they rarely branch. Phycomyces clearly differs from Mucor, however, in its mode of production of zygospores. These, rather than being supported above the substratum by suspensors attached to special zygophores as is the case in Mucor, are formed at the surface of the substratum between tong-shaped suspensors. From the suspensors are produced numerous dichotomously-branched, darkened spines or protuberances which might indicate a resemblance to Absidia. However, Absidia has its zygospores scattered through the aerial portion of the colony and never shows tong-shaped suspensors. In having such suspensors Phycomyces resembles members of the family Pilobolaceae. In that family the suspensors are directly in contact with each other at the surface of the substratum and the zygospore wall is smooth or nearly so, just as in Phycomyces. In these respects there is a resemblance also to the zygospores of Piptocephalis and Syncephalis. However, in neither of these genera nor in the Pilobolaceae are there ornamentations on the suspensors. According to Cutter (1942), the nuclear pattern in Phycomyces blakesleeanus and P. microsporus is different from that of any of the other genera of the Mucorales which he studied. Recent cytological studies have also been made by Robinow (1957) and Harm (1957) on Phycomyces blakesleeanus. It is our opinion that Phycomyces is a genus without any known close relatives in the family Mucoraceae.