A monograph of the genus Gigaspora, incorporating developmental patterns of morphological characters

Abstract

Species concepts within the order Glomales, Zygomycetes, still are in their formative stages and require input from different character sets. Morphological and developmental characters in the genus Gigaspora were compared among nine isolates of five species. To test plasticity of these characters, replicate cultures of the fungi were grown on Sorghum bicolor and Asparagus officinalis under controlled conditions. Sequences of spore wall development were divided into three discrete stages that were identical in all Gigaspora isolates. Neither development nor adult spore morphology of isolates varied significantly between the two host plant species, suggesting strong constraints on plasticity. Gross morphological characteristics of mycorrhizae and extramatrical auxiliary cells did not differ among the various isolates. However, spore size and color varied significantly among species, validating current morphological species concepts within Gigaspora. Comparisons of spore wall development in this study provide a biological rationale for character concepts because characters now can be rooted in a process (development) rather than from static observation. These developmental characters provide the basis for a model of diversity in Gigaspora and its sister genus Scutellospora. In this monograph, the genus Gigaspora is redescribed, along with each species. Three species are rejected as synonyms of other species and a dichotomous key to the remaining species of Gigaspora is presented.

Key Words:

• arbuscular mycorrhizal fungi
• fungal taxonomy
• Glomales
• Zygomycetes