The systematics of arbuscular mycorrhizal fungi in relation to current approaches to biological classification

Abstract

Summary. During the past 30 years, numerous philosophical and procedural discussions have focused on the principles and methods of biological classification. From this have emerged three schools, phenetics, cladistics, and phyletics, each with its own theory of relationships, and its own set of explicit algorithms. At the same time, numerous studies on the economically important arbuscular mycorrhizal fungi have been completed. Some explicit approaches to classification have been made with higher fungi, and cladistic work has just begun on the vesicular arbuscular mycorrhizal (VAM) fungi. Thus it is now appropriate to examine the current status of the systematics of arbuscular mycorrhizal fungi and make suggestions for future work. The highest priority is to establish more refined circumscription of taxa at the lower levels of the hierarchy and to communicate these data and concepts to practicing physiologists, ecologists, etc., so that more rapid progress can be made in these areas. The limits of diversity of the group worldwide should be sought. A standardized identification manual (or atlas) would be most useful. Macromolecular studies are needed to help determine the close relatives of the VAM fungi as well as their interrelationships at the specific and generic levels. Continued emphasis needs to be placed on ontogenetic studies and their impact on variation in characters and states for taxonomic purposes. New quantitative classification approaches need to be used within the group, including phenetics and phyletics. Biogeographic concerns can then be addressed after the taxonomic issues have been more fully settled.

Systematics and taxonomy of the arbuscular endomycorrhizal fungi (Glomales)- a possible way forward

“…One of the crucial propositions put forward by Steussy (1992) is that 'some agreement in the community' needs to be achieved, and he suggests the establishment of a working group for this purpose. This is a timely proposal but such a group must be fully representative of the few taxonomists active in this area.…”

Phylogenetic analysis of the genus Modicella reveals an independent evolutionary origin of sporocarp-forming fungi in the Mortierellales

“…Some authors have considered Modicella species as putative mycorrhizal symbionts (e.g. Manoharachary et al, 2002;Nemec et al, 1981;Stuessy, 1992;Wu and Chen, 1986) but that trophic mode seems unlikely since fresh specimens were readily cultured under axenic conditions (Walker 1923). Walker (1923) collected fresh specimens of M. malleola in Nebraska and was able to germinate spores and obtain pure cultures on a variety of artificial media types.…”

Generation of RAPD‐PCR primers for the identification of isolates of Glomus mosseae, an arbuscular mycorrhizal fungus

“…In the absence of known sexual stages, their identification relies on the structure of their spores or sporocarps (Morton & Benny 1990;Walker 1992). However, many problems are still open, since descriptions of many, especially earlier, species are inadequate and the same term of 'species' has been-questioned as not appropriate for asexual organisms (Stuessy 1992;Walker 1992).…”