Phylogenetic Relationships of Lentinus (Basidiomycotina) Inferred from Molecular and Morphological Characters

Phylogenetic relationships of the basidiomycete Lentinus were investigated using 20 morphological and 133 nucleic acid sequence characters from three regions in the 5' half of the nuclear-encoded large subunit rRNA. Molecular data were obtained from 34 individuals that represent 11 species in Lentinus, nine in the Polyporaceae, eight in the Tricholomataceae, and one in the Corticiaceae. Thanetephorus cucumeris (Tulasnellales) was used as an outgroup for rooting purposes. Most of the sequence variation was in regions that correspond to eukaryote-specific divergent domains DI and D2. Molecular data alone yielded a well-resolved cladogram but morphological data alone were insufficient o resolve phylogenetic relationships. The most resolved cladograms were obtained with a combined analysis of molecular and morphological characters. Bootstrap and decay index measures of branch robustness had a significant positive correlation, but some branches with high bootstrap values were contradicted by near-minimal trees. Monophyly of Lentinus ensu Pegler was not supported. Rather, three monophyletic groups of Lentinus pecies were resolved. These largely correspond to Neolentinus, Panus, and Lentinus . str. The latter appears to be derived from the Polyporaceae, suggesting that lamellae are products of convergent evolution. Fungi are among the most challenging organisms for morphological systematics. At low taxonomic levels many important characters are subtle and preserve poorly in herbarium materials, whereas at higher levels morphological simplicity and a poor fossil record hinder phylogenetic inference. Understandably, increasing numbers of mycological systematists are turning to molecular characters (see reviews by Bruns et al. 1991; Hibbett 1992; Kohn 1992). Here we employ cladistic analyses of ribosomal DNA (rDNA) sequence data and morphological characters to elucidate phylogenetic relationships of Lentinus Fr. Lentinus has been classified in the Tricholomataceae, Agaricales, because it has lamellae and a white spore print (Miller 1972; Miller and Manning 1976). However, it also has anatomical similarities to certain poroid taxa in the Aphyllophorales, and in most modern treatments it is placed in or near the Polyporaceae (Kiihner 1980; Moser 1978; Pegler 1983; Singer 1986). The primary character that supports this placement is the fact that Lentinus pecies are dimitic [the sporocarp is composed of both thin-walled generative hyphae and thick-walled skeletal or ligative hyphae (Corner 1981; Pegler 1983; Pegler and Young 1983)]. Dimiticity is common in the Aphyllophorales, whereas sporocarps of the Agaricales sensu Singer are usually monomitic [composed only of generative hyphae (Corner 1966, 1981; Pegler 1975, 1983; Singer 1986)]. In addition, hyphal pegs, fascicles of sterile hyphae that emerge from the hymenium, are found in certain Lentinus pecies and approximately 10 genera of polypores (Corner 1981; Gilbertson and Ryvarden 1986, 1987; Pegler 1983). Lentinus was monographed by Pegler (1983). Pegler restricted Lentinus to dimitic species, and therefore, transferred the monomitic shiitake fungus, traditionally known as Lentinus edodes (Berk.) Singer, into Lentinula Earle [Collybieae, Tricholomataceae (Pegler 1975)]. Pegler combined Lentinus and Panus Fr. as subgenera. Subgenus Lentinus was restricted to species with ligative hyphae and subg. Panus was restricted to species with skeletal hyphae. Despite Pegler's comprehensive monograph, the delimitation and evolutionary relationships of Lentinus remain controversial. Alternatives to Pegler's treatment have emphasized hyphal anatomy (Corner 1981), the hymenophoral trama (Kiihner 1980; Singer 1986), and wood decay (Redhead and Ginns 1985). Many of the disagreements concern the limits of Lentinus, Panus, and Pleurotus Fr. Redhead and Ginns (1985) created the segregate genera Neolentinus Redhead and Ginns and Heliocybe Redhead and Ginns for nine species of Lentinus ubg. Panus. Pegler hypothesized that "Lentinus represents