Russula section Ingratae subsections Foetentinae and Pectinatae - introduction

Anna Bazzicalupo and RBGE's Dr Stephan Helfer introduce Anna's revision of this aromatic group of Russulas:

The species of Russula subsection Foetentinae in Britain have been revised by Anna Bazzicalupo in 2011 during her MSc project at the Royal Botanic Garden Edinburgh. Based on spore ornamentation and a preliminary molecular analysis, six species and one variety are recognised. A key to the species of the section Ingratae and subsections Foetentinae and Pectinatae is given. The type specimens of the species in Foetentinae are discussed and diagnostic characters for the species are reported. Some of the field characters (e.g. odour or taste) used for identification have been used inconsistently in the past.

The genus Russula, first described by Persoon, is a group of obligate ectomycorrhizal fungi. Ectomycorrhizal fungi play key roles in ecosystem functions including the cycling of carbon, nutrients and minerals and linking forest trees in a common mycorrhizal network. Their important role as ectomycorrhizal symbionts has been documented not only in arctic alpine regions but also in the tropics. The number of species in the genus is unknown and estimates vary according to the source consulted, for example Singer (1975) recognises 275 species. Numbers of species have been given regionally, such as 85 species for the Pacific Northwest or 135 for Switzerland (Kränzlin, 2005). A rough estimate of the total number of species worldwide is 750 (Rinaldi et al., 2008). Russula as a genus is easily identified, but identification problems arise when trying to distinguish the species within the genus.

The present key considers the section Ingratae, which was first described by Quélét in 1888 and has been revised recurrently. Among the characteristics of this section are the fragrant nature (from foetid to almonds and marzipan) and the light-coloured spore print, which varies from pure white to cream.

The instability of the classification of Russula and its sections is possibly an indication of the difficulty in finding morphological characters that are consistent and work well throughout the group. In 1930, Crawshay examined spore ornamentation in Russula by staining spores with Melzer’s iodine solution; he suggested that the infrageneric relationships could be clarified by using spore ornamentation. Even though this character has not been helpful in classifying the entire genus, it is useful and widely used in the literature when dealing with taxa inside smaller sections. Researchers have used Scanning Electron Microscopy (SEM) techniques to investigate in more depth the spore ornamentation of Russula.

Molecular analyses can provide additional sets of data on which to base classifications and have become a powerful tool to solve taxonomic problems such as those encountered in Russula. A new concept of the Ingratae and the Foetentinae, which is similar to Bon’s (1989), is presented. The systematic amendments to these taxa reflect the findings of both morphological and molecular investigations.