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Orchidaceae is one of the most species-rich angiosperm families, and all orchids are fully dependent on fungi for their seed germination and their life cycle. The level of specificity of the association between orchid species and fungi can be related to the number of co-occurring orchid species. To investigate orchid mycorrhizal associations in adult-photosynthetic orchids, 16 Mediterranean orchid species belonging to 4 genera (Anacamptis, Ophrys, Orchis, and Serapias) at 11 different sites were subjected to DNA-based analysis. Eighteen operational taxonomic units representing two fungal families, Tulasnellaceae and Ceratobasidiaceae, were identified. All examined orchid species associated with different mycorrhizal fungi. Interestingly, there was a positive correlation between number of orchid species and number of mycorrhizal. Monospecific populations showed a lower number of fungi, while sympatric populations had a higher number of mycorrhizal fungi. Our results showed that Mediterranean orchid...

A new genus, Heterorepetobasidium, is proposed to accommodate two new species, H. subglobosum and H. ellipsoideum, recently collected in Taiwan. These species have apically, partially septate basidia, strongly swollen sterigmata, and repetobasidia. The systematics of the new taxa and related ones, inclusive of Ceratobasidium and the Ceratobasidiaceae, are reinterpreted.

The phylogenetic relationships of anasto- mosis groups (AG) of Rhizoctonia associated with Cer- atobasidium and Thanatephorus teleomorphs were de- termined by cladistic analyses of internal transcribed spacer (ITS) and 28S large subunit (LSU) regions of nuclear-encoded ribosomal DNA (rDNA). Combined analyses of ITS and LSU rDNA sequences from 41 isolates representing 28 AG of Ceratobasidium and Thanatephorus supported at least 12 monophyletic groupings within Ceratobasidium and Thanatephorus. There was strong support for separation of Cerato- basidium and Thanatephorus, however, six sequences representing different AG of Ceratobasidium grouped with certain sequences within the Thanatephorus clade. Phylogenetic analysis of ITS sequence data from 122 isolates revealed 31 genetically distinct groups from Thanatephorus (21 groups) and Cerato- basidium (10 groups) that corresponded well with previously recognized AG or AG subgroups. Al- though phylogenetic analysis of ITS sequences pro- vided evidence that several AG of Ceratobasidium may be more closely related with some AG from Thana- tephorus, these relationships were not as strongly sup- ported by bootstrap analysis.

The only tremellaceous fungus previously described in which the basidium is characterized by the formation of incomplete septa is Metabourdotia, found by Olive (1957) in Tahiti. During a collecting tour in Guatemala in the summer of 1963, the writer found the fungus to be described in this paper as a new genus. It is at once apparent that the new fungus and Metabourdotia are related by virtue of the incomplete septation of their basidia, but whereas Metabourdotia forms sterigmata 2 that show a close affinity with similar structures of the Tremellaceae or of the Ceratobasidiaceae, the basidia of the Guatemalan fungus produce sterigmata that are diagnostic of those found in the Tulasnellaceae. The Guatemalan collection is therefore closely identified with this family but is distinguished from all other members thereof by its partially septate basidia. A new genus is therefore proposed to accommodate it.