Observations on Asexual and Sexual Reproductive Structures of the Choanephoraceae

SUMMARY

Twenty isolates of Choanephora cucurbitarum (Berk. & Rav.) Thaxter and five designated Blakeslea trispora Thaxter were obtained from soil and other sources. Experimental studies were conducted and observations made on the fundamental morphology of “conidia” and sporangioles. The “conidia” of Choanephora are truly monosporous sporangioles and similar, except for the number of spores developed in each, to sporangioles of isolates designated as Blakeslea. Striations have been observed on the walls of all spore types produced by all of the isolates of the Choanephoraceae investigated. This characteristic appears to be of fundamental diagnostic importance for the family.

The formation of zygospores between the tips of twining branches of fertile hyphae is the characteristic method of zygospore development in the Choanephoraceae. This type of zygospore formation and other morphological characteristics, such as spore striations and the production of aerial sporangia and sporangioles on separate sporangiospores, combined, distinguish species belonging to the Choanephoraceae and separate them from other fungi belonging to the Mucorales. Observations reported here substantiate Sinha's proposal that the principal difference between Blakeslea and Choanephora is not of generic significance and, therefore, Blakeslea must be considered a synonym of Choanephora. Choanephora conjuncta is concluded to be a synonym of C. cucurbitarum.