Nancy S. Weber

Phylogenetic relationships among ascomycetous truffles and the true and false morels inferred from 18S and 28S ribosomal DNA sequence analysis

Phylogenetic relationships among asco- mycetous truffles and the true and false morels were examined by using sequences from two nuclear en- coded ribosomal DNA genes. The data consist of 18S rDNA and partial 28S rDNA sequences for 29 taxa. Individual and combined data sets were analyzed by maximum parsimony (MP), neighbor-joining (NJ) and maximum likelihood (ML) methods. Parsimony analysis of the combined data set, which contained 3 published 18S sequences and consisted of 2358 nu- cleotide characters, yielded a single most parsimoni- ous tree of 1728 steps. The results indicate that the hypogeous ascomycetous truffle and trufflelike taxa studied represent at least 5 independent lineages within the Pezizales. Results also suggest that several epigeous and most hypogeous taxa have been mis- placed taxonomically. Bootstrap analyses show strong support for a Tuberaceae-Helvellaceae clade which is a monophyletic sister group of a Morchellaceae-Dis- cinaceae clade. Rhizina is a sister group to both of these clades in the MP and ML trees while in the NJ tree it is a sister of the Morchellaceae-Discinaceae clade. MP, ML, and NJ tree topologies indicate that Rhizina should be removed from the Helvellaceae and classified in a monotypic family, the Rhizinaceae. A phylogenetically-based classification for these fungi is proposed together with emendations of 4 families.

Phylogeny and historical biogeography of true morels (Morchella) reveals an early Cretaceous origin and high continental endemism and provincialism in the Holarctic.

True morels (Morchella, Ascomycota) are arguably the most highly-prized of the estimated 1.5 million fungi that inhabit our planet. Field guides treat these epicurean macrofungi as belonging to a few species with cosmopolitan distributions, but this hypothesis has not been tested. Prompted by the results of a growing number of molecular studies, which have shown many microbes exhibit strong biogeographic structure and cryptic speciation, we constructed a 4-gene dataset for 177 members of the Morchellaceae to elucidate their origin, evolutionary diversification and historical biogeography. Diversification time estimates place the origin of the Morchellaceae in the middle Triassic 243.63 (95% highest posterior density [HPD] interval: 169.35-319.89) million years ago (Mya) and the divergence of Morchella from its closest relatives in the early Cretaceous 129.61 (95% HPD interval: 90.26-173.16) Mya, both within western North America. Phylogenetic analyses identified three lineages within Morchella: a basal monotypic lineage represented by Morchella rufobrunnea, and two sister clades comprising the black morels (Elata Clade, 26 species) and yellow morels (Esculenta Clade, 16 species). Morchella possesses a Laurasian distribution with 37/41 species restricted to the Holarctic. All 33 Holarctic species represented by multiple collections exhibited continental endemism. Moreover, 16/18 North American and 13/15 Eurasian species appeared to exhibit provincialism. Although morel fruit bodies produce thousands of explosively discharged spores that are well suited to aerial dispersal, our results suggest that they are poorly adapted at invading novel niches. Morels also appear to have retained the ancestral fruit body plan, which has remained remarkably static since the Cretaceous.

Isotopic evidence indicates saprotrophy in post-fire Morchella in Oregon and Alaska.

We assessed the nutritional strategy of true morels (genus Morchella) collected in 2003 and 2004 in Oregon and Alaska, 1 or 2 y after forest fires. We hypothesized that the patterns of stable isotopes (δ13C and δ15N) in the sporocarps would match those of saprotrophic fungi and that radiocarbon (Δ14C) analyses would indicate that Morchella was assimilating old carbon not current-year photosynthate. We compared radiocarbon and stable isotopes in Morchella with values from concurrently collected foliage, the ectomycorrhizal Geopyxis carbonaria (Alb. & Schwein.) Sacc., the saprotrophic Plicaria endocarpoides (Berk.) Rifai, and with literature to determine isotopic values for ectomycorrhizal or saprotrophic fungi. Geopyxis, Plicaria and Morchella, respectively, were 3‰, 5‰ and 6‰ higher in 13C than foliage and 5‰, 7‰ and 7‰ higher in 15N. High 15N enrichment in Morchella indicated that recent litter was not the primary source for Morchella nitrogen, and similar 13C and 15N enrichments to Plicaria suggest that Morchella assimilates its carbon and nitrogen from the same source pool as this saprotrophic fungus. From radiocarbon analyses Morchella averaged 11 ± 6 y old (n = 19), Plicaria averaged 17 ± 5 y old (n = 3), foliage averaged 1 ± 2 y old (n = 8) and Geopyxis (n = 1) resembled foliage in Δ14C. We conclude that morels fruiting in post-fire environments in our study assimilated old carbon and were saprotrophic.

Ecology and Distribution of Desert Truffles in Western North America

The four major deserts of North America are situated in the western USA and northern Mexico: the Great Basin Desert, Mojave Desert, Sonoran Desert, and Chihuahuan Desert. Together they cover about 1,244,000 km2. Two genera of North American desert truffles, Carbomyces with three species and Stouffera with one, are endemics. A third genus, Mattirolomyces with one endemic species in North America, occurs in both northern and southern hemispheres from mesic forests to semiarid and arid habitats in three other continents. The largest and also the coldest of the North American deserts, the Great Basin Desert, and the smallest and hottest Mojave have each produced only one desert truffle collection so far. The Sonoran, also relatively hot, accounts for only two. In contrast, the relatively cold Chihuahuan, which extends from southern New Mexico south into Mexico’s central plateau, has produced 17 truffle collections from New Mexico and about 30 from Chihuahua. Too little data are available on habitat requirements of the North American desert truffles to explain this skewed distribution. However, it likely reflects a concentration of early collecting efforts around the Jornada Basin Long-Term Ecological Research Site, originally established in 1912, that has attracted desert researchers for a century. Ten of the 17 collections in the Jornada vicinity were found by mycologist W. H. Long and his students and associates in 1941. More recently, active collecting in the Chihuahuan Desert of Chihuahua, Mexico, has added about 30 desert truffle collections. Both seem to reflect a convergence of the right people at the right place in a good truffle year.