Tricholosporum caraibicum ( Basidiomycota, Tricholomataceae ), a new species from the Dominican Republic

A new species in the genus Tricholosporum, collected in the Dominican Republic, is taxonomically delimited based on morphological data. A detailed description, microscopic drawings and a colour plate of fresh material are presented. The new species is well circumscribed by the small cruciform to stauriform spores and mucronate, fusiform to ampullaceous and pigmented cystidia. A key to the accepted species of Tricholosporum is provided.


Introduction
The genus Tricholosporum was established by G. Guzmán to accommodate Tricholoma goniospermum Bres. and Tricholosporum subporphyrophyllum Guzmán, based on the difference in their spore shape, compared to that of true Tricholoma (Fr.) Staude species (Guzmán 1975). Singer (1986), however, did not recognize Tricholosporum as a distinct genus and placed Tricholoma goniospermum and allied species, such as as Tricholoma porphyrophyllum S. Imai, Tricholosporum subporphyrophyllum and Gymnopus atroviolaceus Murrill in Tricholoma (Fr.) Staude section Iorigida Singer, typified by Tricholoma pseudosordidum Singer, an opinion shared, among others, by Bohus (1985). In Bon's (1991) taxonomic account of the European species of Tricholoma, Tricholosporum is treated as a subgenus of Tricholoma (see also Bon & Braiotta 1989, where the new combination Tricholoma subgen. Tricholosporum is firstly introduced).
In recent years most authors treated Tricholosporum as a genus in its own right (Baroni 1982, Halling & Franco Molano 1996, Reid et al. 1998, Bohus et al. 1999, Contu & Mua 2000, Boisselet & Moreau 2008, Riva 2008, Fernandez Vicente et. al. 2010, Christensen & Heilmann-Clausen 2013 and in the present paper this opinion is followed. Unfortunately no molecular analysis has included species of the genus. Tricholosporum appears to be a widespread genus as members are known from North and South America, Africa, Asia, Canary Islands and Europe (Contu & Mua 2000). Tricholosporum can be distinguished from Tricholoma based on the rhomboid to cruciform spores (Baroni 1982, Guzmán 1975, 1994, Contu & Mua 2000.
During field work in the Dominican Republic in late 2013, basidiomata of a very beautiful agaric were collected; close micromorphological examination revealed the presence of cruciform *Corresponding Author: Alfredo Vizzini -e-mail -alfredo.vizzini@unito.it 430 basidiospores and a lack of siderophilous grana in the basidia, suggesting that the specimens belong to the genus Tricholosporum.
No name being available for this very remarkable agaric, we therefore describe it as a new species, Tricholosporum caraibicum

Materials & Methods
Macroscopic descriptions were based on the study of fresh material by the first author. A total of 6 basidiomes were studied. The microscopic descriptions and the micromorphological data are based on herbarium material reinflated by using water and L4 and coloured with Congo Red and Phloxin B. Cotton Blue was utilized to examine the siderophilous grana in the basidia and to detect gelatinised tissues in the pileal surface. Spore measurements are based on means of 32 spores, originating from three basidiomes. The taxonomy of Baroni (1982) was followed for the description of the new species. The Latin description of the new species was deposited in Mycobank (http://www.mycobank.org/DefaultPage.aspx). Herbarium acronyms follow Thiers (2014). Author citations follow the Index Fungorum, Authors of Fungal Names (www.indexfungorum.org/authorsoffungalnames.htm).  16.XII.2013, leg. C. Angelini (herb. JBSD 125216, holotypus).

Tricholosporum caraibicum
Habit resembling that of Calocybe ionides/Lepista sordida. Pileus 30-40 mm, not very fleshy, not cartilaginous, convex, then plano-convex, widely and obtusely umbonate, the margin involute for a long time, dry, opaque, not hygrophanous, at first fibrillose-felted (due to very thin, white hairs) then finely velvety but smooth towards the centre, deeply violaceous-lilac (but fading yellow to citrine-yellow at the centre on age with the margin remaining violet), with peculiar white or yellowish elongated spots or maculae. Lamellae (with lamellulae) slightly ventricose, normally crowded to crowded, thickish, emarginate-adnexed, violaceous, yellowing when handled, with concolorous and slightly eroded edge. Stipe 40-50 × 6-7 mm, solid, fistulose-hollow, cylindric, sometimes enlarged or tapered downwards, bluishviolaceous, fading to whitish on age, especially toward the base, adpressed fibrillose, covered by an abundant white flocculose pruina which is more abundant and intermixed with flocci at the apex, the base with thin, white rhizomorphous filaments. Context thin, 2-3 mm thick, cream yellowing in the pileus, cream-violaceous and unchanging in the stipe. Smell not peculiar, fungineous, taste at first similar but then rather strongly bitter. Edibility unknown. Spore-print: white.
Habitat and known distribution -Gregarious, on soil in deciduous forest. Autumn. Very rare and so far known only from Dominican Republic.