In the past decade, there has been a large increase in the number of descriptions of species in the Glomales (Morton and Benny, 1990) and an enormous amount of research into the effects some of these fungi have on plant growth. The proliferation of species and the variation in the standards of description has inevitably caused much uncertainty in the mind of the scientist who may simply desire to have a name to attach to an experimental organism but who does not desire to become involved with taxonomy (Walker, 1985). Unfortunately, identification of this group of fungi is difficult. VAM fungi are obligate symbionts and can not yet be cultured on artificial media common in microbiology and phytopathology. Their classification is basedon morphology of their resting spores. This implies that, for identificationpurposes, the fungi must have sporulated and that spores must be separated from the substrate or soil in which they started their reproductive phase on a host plant (Sieverding, 1991). In this session, main features of the genera in Glomales and the techniques how to increase these species are introduced and illustrated.

Besides, two more new genera in Glomales have (will) be proposed, i.e., Glomites (Taylor, et al., 1995), and Jimtrappea (Wu and Lin, 1997).

Acaulospora Gerdemann & Trappe emend. Berch

Etymology: Greek, a-(without), caulos (stem), and spora (spore), referring to the sessile spores.

Spores produced in soil or in sporocarps that may attain several cm in length; spores globose, subglobose, ellipsoid, or broadly fusiform, with oily contents; borne laterally on the sbutending hypha of large, terminal relatively thin-walled, sporogenous saccule. Terminal sporogenous saccule may be up to twice the size of spore; contents transferred to developing spore. Spore composed of essentially two distinct, separable wall groups; at least part of outer is continuous with wall of subtending stalk, may be pigmented, laminated or composed of distinct walls, and variously ornamented; inner is composed of one or more walls that are usually membranous, hyaline, may be laminated, ornamented, and stalk that subtends spore is occluded by part og the outer spore wall group. go back to the top

Entrophospora Ames & Schneider

Etymology: Greek, en (within), trophos (nourished or reared), and spora (spore), referring to the spore being reared within the vesicular stalk.

Azygospores produced singly in soil by expansion within the stalk of the mother vesicle. Mother vesicle thin walled, dense white, becoming empty as contents are transferred to developing spore. Walls of vesicular stalk expand to accommodate spore, forming a clear outer membrane tightly appressed to the spore. Spore wall continuous except for funnel-shaped protion which extends into the mother vesicle and is closed by a thickened plug.

Entrophospora Ames & Schneider emend. Wu

Spores produced singly in soil. Sporogenesis started inside the stalk of a sporiferous saccule by the formation of a septum in the lower channel of the stalk. The cytoplasm within the saccule seemed the major source for the spore formation. When the cytoplasm flowed downward, the central part of stalk swelled and tiny vacuoles were formed at the periphery of saccule. As the primordial spore was differentiated inside the stalk, another septum was formed right below the saccule. After spores mature, the terminal vesicles of saccules and the lower hyphal stalks degenerate and leave two scars. go back to the top

Gigaspora Gerdemann & Trappe emend. Walker & Sanders

Etymology: Greek, giga-(giant) and -spora (spore), referring to the exceptionally large spores typically produced by members of the genus.

Spores produced singly in soil, large variable in shape, usually globose or subglobose but often ovoid, pyriform or irregular, especially when constrained during formation, borne on a bulbous suspensor-like cell, usually with a narrow hypha extending from one or more peg-like projections towards the spore. Spore wall structure of a single wall group, lacking flexible (membranous or coriaceous) walls. One or more germ tubes produced directly through the spore wall near the base. Thin-walled, echinulate or finely papillate auxiliary cells borne in osil, on straight or coiled hyphae, formed singly or in clusters. Forming endomycorrhizae with arbuscules and hyphal coils, but without vesicles. go back to the top

Glomus Tulasne & Tulasne

Etymology: Latin, glomus (a ball of yarn), possibly in reference to the sometimes rounded and cottony appearance of the species for which the Tulasnes erected the genus.

Chlamydospores borne terminally on single (rarely two) undifferentiated, nongametangial hyphae in sporocarps or individually in soil. Spore contents at maturity separated from attached hyphae by a septum or occluded by spore wall thickening. go back to the top

Sclerocystis Berkeley & Broome

Etymology: Greek, sclero- (hard) and -kystis (bladder), referring to the small, very hard, rounded sporocarps of the type species.

Chlamydospores arranged side by side in a single layer, elongated, radiating out from a central plexus of hyphae.

Sclerocystis Berkeley & Broome emend. Wu

Sporocarps globose or subglobose or hemispherical, enclosed by a peridium or naked, with a multihyphal stipe or monohyphal stalks; Chlamydospores arranged side by side in a single layer, radiating out from a central plexus of hyphae; Central plexus composed of a broad, stellate thick-walled cell or interwoven hyphae; Development of chlamydospores within sporocarps synchronous or asynchronous; Sidephores frequently producing from the base of chlamydospores, becoming spores or intersporal hyphae.  go back to the top

Scutellospora Walker & Sanders

Etymology: Latin, scutellum- (small shield) and spora, (spore), referring to the production of germination shields in spores of members of the genus.

Spores produced singly in soil (or rarely in cortical cells of roots), large, variable in shape, usually globose or subglobose, but often ovoid, obovoid, pyriform or irregular especially when constrained during formation; borne on a bulbous suspensor-like cell, usually with a narrow hypha extending from one or more peg-like peg-like projections towards the spore. Spore wall structure of at least two wall groups, with one or more flexible membranous or coriaceous walls in the inner group or groups. Germination by means of one or more germ tubes produced near the spore base from a germination shield formed upon or within a flexible inner wall. Thin-walled, knobby or broadly papilate auxiliary cells borned in soil, on straight or coiled hyphae, formed singly or in clusters. Forming endomycorrhizas with arbuscules and hyphal coils, but without vesicles. go back to the top

Glomites Taylor, Remy, Hass et Kerp

Glomites rhyniensis Taylor, Remy, Hass et Kerp

Etymology: The generic name Glomites underscores the similarity to the extant genus Glomus; the ending ites is used to designate a fossil taxon, as discussed by Pirozynski and Weresub (1979). The specific epithet rhyniensis denotes the Rhynie chert collecting locality.

Extraradical, aseptate hyphae up to 25 ƒÝm in diam, occasionally occurring in bundles, hyphal wall two-parted, rarely branched; intraradical hyphae of two types, one consisting of aseptate hyphae 8-14 mm in diam, thin-walled, extensively branched in hypodermis, branches produced in acute angles of 30-60¢X, occasionally with slight projections representing former site of deteriorated hyphae; other narrower hyphal branches produced at more right angles, narrow (5 mm) and giving rise to solitary, occasionally multiple, terminal globose-elongate spores ranging from 50-80mm; spore wall multilayered with inner layer continuous with subtending hypha, basal septum absent; other narrow hyphal branches penetrate cortical cell wall to form highly branched arbuscules, arbuscule with basal stalk approximately 2 mm in diam, and forming fine distal tips, sometimes slightly swollen; arbuscules confined to narrow (one to four cells wide) outer cortical zone beneath hypodermis. go back to the top

Jimtrappea Wu & Lin

Etymology: Latin, Jimtrappea (Jim Trappe), in honor of Dr. J. Trappe, Oregon State University, in recognition of his contribution to our knowledge of mycorrhizal fungi.

Sporocarps unknown. Spores produced singly in the soil and formed directly within the sporiferous saccules. Sporiferous saccules formed at terminal or intercalary part of hypha. Walls of hypha expanded to accomodate spore, forming a clear outer layer tightly appressed to the spore. Stalk of sporiferous saccule degenerated, leaving circular attachment(s). Spore germination by growing germ tube through spore wall and producing vesicular structures in the end of germinating hyphae.  go back to the top

The spore morphology of Jimtrappea is close to Entrophospora and Acaulospora, because spores of Jimtrappea are ornamented by a large circular attachment, 17.5-42.5 mm diam and sometimes are accompanied with up to 12 smaller scars, if sporiferous saccules are generated intercalarily and connected with many slender hyphal branches. Based on our observation that germination pore is 5-12 mm diam, about the size of smaller scars, these smaller attachments could be the residual trace of germinating hyphae and multiple germination seems possible in this genus. However, the spores of Jimtrappea are very much distinguished from Acaulospora and Entrophospora, especially by their unique type of spore ontogeny and germination (Fig. 1).

Sporogenesis is initiated by the formation of sporiferous sacccule which is filled up with dense cytoplasm and later, septa are formed in the lower part of the hyphal stalk of the saccule and other slender branches. Septal formation is an important stage in the sporogenesis of Entrophospora, Acaulospora (Wu, et. al., 1995a) as well as in Jimtrappea. After the formation of septum, most of the cytoplasm within the sporiferous saccule is provided as the source for spore differentiation (Fig. 7). In the case of Jimtrappea, the septum is frequently formed in the very end of the hyphal stalk which is up to 350 ƒÝm long, therefore it is not easy to find.

Because the spores of Jimtrappea are produced directly inside the sporiferous saccule, the spores are very often attached by a broad and thin-walled, tapering hyphal stalk of sporifeous saccule (Figs. 1-3) and might be confused as Glomus species. At this stage, the spore looks like an egg laid in a sac. The sporogenesis of Jimtrappea is obviously different from Glomus. In contrast, the spores of Entrophospora are usually connected with an empty hyphal terminus by an interconnecting hypha, having a dumbbell-shaped configuration.

Besides, the types of spore germination of Entrophospora and Acaulospora are different from that of Jimtrappea. The former genera produce spiral germ shields; however, the latter forms a germ tube directly throuhg spore wall.

Strictly speaking, the ephemeral outer wall of Jimtrappea macrospora could not be counted as a part of spore wall, based on spore ontogeny. A real outer spore wall, should be wall 2. In Entrophospora kentinensis, wall 2 in early ontogeny stage, is very elastic and extends downward the septum in the lower part of the saccule stalk (Wu, et. al., 1995a, Fig. 2). Nevertheless, in the case of Jimtrappea macrospora, the wall 2 after differentiation, did not extend into the hyphal stalk, in stead staying inside the saccule. Consequently, an ¡§acaulospore¡¨ is generated within the saccule. In rare case, part of spore wall may be expelled into the space of hyphal stalk for a very short distance, but it could not be an attachment hypha as in Glomus (Fig. ).

Based on our observation, i.e. (i) ¡§acaulospores¡¨ are ornamented with a large double-circled attachment up to 42.5 mm diam, (ii) sporogenesis is initiated by a sporiferous saccule and the cytoplasm inside the saccule is delimited by a septum formed in the lower position of saccule stalk, (iii) a ¡§bump¡¨ swelling in the lower part of saccule stalk looks like the early stage of spore development in Acaulospora, we suspect that Jimtrappea is very much related to Acaulospora and Entrophospora, although the germination type is different from both genera. Jimtrappea may origin from Acaulospora, since the ¡§bump¡¨ is the intial stage for the spore formaion of the latter genus. Normally, the cytoplasm in the sporiferous saccule will flow toward the saccule stalk from the lateral side of which a spore is blown out. We give a hypothesis that gene(s) mutation occurs, which mediate the transfer of cytoplasm and causes the cytoplasm retained in the saccule. This mass of cytoplasm is finally differentiated into an ¡§acaulospore¡¨ directly within the saccule.

Since sporogenesis of Jimtrappea is similar to Acaulospora and Entrophospora, they all produce spores without attachment hyphae and spores are ornamented with cicatrices. Therefore, Jimtrappea is treated under the family Acaulosporaceae. go back to the top

Harley, J. L. and S. E. Smith. 1983. Mycorrhizal symbiosis. Academic Press, London.

Morton, Joseph B. and G. L. Benny. 1990. Revised classification of arbuscular mycorrhizal fungi (Zygomycetes): A new order, Glomales, two new suborders, Glomineae and Gigsporineae, and two new families, Acaulosporaceae and Gigasporaceae, with an emendation of Glomaceae. Mycotaxon 37:471-491.

Pirozynski, K. A. and L. K. Weresub. 1979. The classification and nomenclature of fossil fungi. Pp. 653-688. In: The whole fungus, the sexual-asexual synthesis. Vol.2. Ed. B. Kendrick, Proc. 2^nd Int. Mycol. Conf., Univ. Calgary, Kananaski, Alberta. Natl. Mus. Nat. Sci., Natl. Mus. Canada and Kananaskis Foundation, Ottawa, Canada.

Schenck, N. C. and Y. Perez (eds.) 1990. Mannual for the identification of VA mycorrhizal fungi. Synergistic Publications, Gainesville.

Sieverding, E. 1991. Vesicular-arbuscular mycorrhiza management in tropical agrosystem, Deutsche Gesellschaft fur Technische Zusammenarbeit (GTZ) GmbH, Germany.

Taylor, T. N., W. Remy, H. Hass, and H. Kerp. 1995. Fossil arbuscular mycorrhizae from the early Devonian. Mycologia 87: 560-573.

Trappe, J. M. 1987. Phylogenetic and ecologic aspects of mycotrophy in the angiosperms from an evolutionary standpoint. In: Safir, G. R. (ed.) Ecophysiology of VA Mycorrhizal plants, p 5-25. CRC Press, Boca Raton.

Walker, C. 1985. Taxonomy of Endogonaceae. In: Randy Molina (ed.) Proceedings of the 6^th North American Conference on Mycorrhizae, P 193-198. Forestry Resarch Laboratory.

Wu, Chi-Guang and Suh-Jen Lin. 1997. Glomales of Taiwan: VII. Jimtrappea and J. macrospora, new taxa of Acaulosporaceae (Glomaceae). Mycotaxon (in press). go back to the top