Acaulospora alpina, a new arbuscular mycorrhizal fungal species characteristic for high mountainous and alpine regions of the Swiss Alps Fritz Oehl Zuzana Sy ´korova ´ Dirk Redecker Andres Wiemken Zurich-Basel Plant Science Center, Institute of Botany, University of Basel, Hebelstrasse 1, CH-4056 Basel, Switzerland Ewald Sieverding 1 Institute of Plant Production and Agroecology in the Tropics and Subtropics, University of Hohenheim, Garbenstrasse 13, D-70593 Stuttgart, Germany Abstract: Acaulospora alpina sp. nov. forms small (65–85 mm diam), dark yellow to orange-brown spores laterally on the neck of hyaline to subhyaline sporiferous saccules. The spores have a three-layered outer spore wall, a bi-layered middle wall and a three- layered inner wall. The surface of the second layer of the outer spore wall is ornamented, having regular, circular pits (1.5–2 mm diam) that are as deep as wide and truncated conical. A ‘‘beaded’’ wall layer as found in most other Acaulospora spp. is lacking. The spore morphology of A. alpina resembles that of A. paulinae but can be differentiated easily by the unique ornamentation with the characteristic pits and by the spore color. A key is presented summariz- ing the morphological differences among Acaulospora species with an ornamented outer spore wall. Partial DNA sequences of the ITS1, 5.8S subunit and ITS2 regions of ribosomal DNA show that A. alpina and A. paulinae are not closely related. Acaulospora lacunosa, which has similar color but has generally bigger spores, also has distinct rDNA sequences. Acaulospora alpina is a characteristic member of the arbuscular mycorrhizal fungal communities in soils with pH 3.5– 6.5 in grasslands of the Swiss Alps at altitudes between 1800 and 2700 m above sea level. It is less frequent at 1300–1800 m above sea level, and it so far has not been found in the Alps below 1300 m or in the lowlands of Switzerland. Key words: Alps, Acaulosporaceae, Acaulospora paulinae, Acaulospora lacunosa, Glomeromycetes, key, molecular identification, mycorrhiza, spore morphology, phylogeny, taxonomy INTRODUCTION At high altitudes, in the mountainous and alpine regions of the Swiss Alps extending from 1000– 3000 m above sea level (a.s.l.), we have observed an astonishingly high diversity of arbuscular mycorrhizal (AM) fungal species (Oehl unpubl). Spores of about 60 known species of the Glomeromycota (Schu ¨ ssler et al 2001) could be identified from different grasslands growing on soils that had developed on siliceous and calcareous bedrocks. Some of the species were new and recently have been described (Oehl and Sieverd- ing 2004, Oehl et al 2005a). Among the AM fungi, species belonging to the genus Acaulospora were particularly prominent and relatively much more abundant than in the lowlands of Switzerland. Here we describe a new Acaulospora species under the epithet A. alpina that was found exclusively in the Alps at altitudes .1300 m a.s.l. The genus Acaulospora was described by Gerde- mann and Trappe (1974) who also presented the first key for the two species known at that time. The key differentiated a species known to produce spores with a smooth surface (A. laevis) from another one with an ornamented surface (A. elegans). Today we know 18 Acaulospora spp. with smooth spore surfaces and 15 Acaulospora spp. (including A. alpina) with ornamen- tation of the outer spore wall. Schenck et al (1984) presented the latest key to the ornamented species of Acaulospora. They used spines, tubercles, ridges, folds, pits or cracks as differentiating features for the spore wall ornamentations. We use similar characteristics and we present an updated key for Acaulospora spp. with ornamented spore walls. In recent years molecular biological tools have been applied to identify AM fungi (Clapp et al 1995, Redecker 2000, Oehl et al 2005a). Environmental rDNA sequences are rapidly increasing in number in the public databases. However only a few DNA sequences of Acaulospora originating from morpho- logically characterized spores are available. This is also true for the highly variable rDNA internal transcribed spacer (ITS) region, which is a useful tool to distinguish many species-level AM fungal taxa (Redecker et al 2003). Some of these database sequences show strong similarity to fungal groups other than the Glomeromycota and are more likely to originate from contaminant organisms (Millner et al 2001). Therefore there is a clear need for rDNA sequences from described Acaulospora species. Accepted for publication 6 Jan 2006. 1 Corresponding author. E-mail: sieverdinge@aol.com Mycologia, 98(2), 2006, pp. 286–294. # 2006 by The Mycological Society of America, Lawrence, KS 66044-8897 286