Omphalotus mexicanus is a rare large conspicuous well known mushroom endemic to southwestern Mexico. Its is associated to big old Quercus trees. Even while its EOO is large, its suitable habitat within area is severely fragmented and declining. Its estimated population is based on extensive search resulted in just 25 records in 35 years, so its rarity is a rubust assumption.
Assessed as Vulnerable (EN) under criterion C2a(i) as the number of estimated localities is not more than 150, population estimate below 50 mature individuals in each subpopulation, and with ongoing and projected habitat loss and fragmentation due to change in land use and logging of 20%-40% in the next 50 years.
Omphalotus mexicanus has a pileus 15-100 mm in diameter, convex to depressed, glabrous, blackish blue to black. Lamellae decurrent, light blue to blackish. Stipe 70-140 x 5-15 mm, central or eccentric, smooth to slightly scaley, color lighter than pileus, yellow-orange to orange-reddish at base. Context fleshy purple-blue and more leathery then stipe. Spore print white. Basidiospores 6.5-8.4 x (4.5-) 5.2-6.5 µm, globose to subglobose, smooth, hyaline in KOH, inamyloid. This species differs from O. olearius (DC. ex Fr.) Sing. and O. olivascens H.E. Bigelow, O.K. Mill. & Thiers because of its blue-blackish sporocarp color versus yellow-orange, and olivaceus sporocarp color, respectively. Also, O. mexicanus has amyloid pseudocystidia and smaller cheilocystidia (Mora & Guzmán, 1983).
Many of the Omphalotus mexicanus is an uncommon endemic to Mexico where it associates exclisively to mature oak forests. Most records before 1995 are located in forestlands that now are transformed into agricultural or grazing fields. These forests are also endangered because Quercus species are used as timber. This species should be protected because of its limited distribution and because of the destruction of its natural habitat and historical populations.
Restricted to southwestern Mexican temperate and subtropoical Quercus forests. Recorded from Tapalpa, Mazamitla, Tequila volcano and Sierra de Manantlan in Jalisco state; Oaxaca Sierra; Michoacan state, near Morelia state, and the State of Mexico (GBIF, 2018). Omphalotus mexicanus was also reported by Kirchmair et al. (2002, 2004) from Guatemala.
All subpopulations of this species have been recorded from southwest Mexico, plus one unconfirmed record from Guatemala. There are several subpopulations recorded from Jalisco state growing in oak-pine forests, including the type collection in Tapalpa. Other records from Jalisco include one each from Mazamitla, 2.5 km S from La Manzanilla, 7.5 km SW from San Miguel Cuyutlán, three locations near crater of Tequila volcano, 1 km SW from Chilacayote, Cerro las Capillas at Sierra de Manantlán, 7 km SW from El Nogal, and one 5 km E from Los García. There are four subpopulations recorded from the Oaxaca mountains: 4.7 km SW from San Bartolo Soyaltepec, 2.5 km NE from La Estancia, 7.5 km NE from San Juan Bautista Atlahuca, and 2.3 km W from San Francisco Teopam. Four subpopulations are recorded from Michoacan state: near Contepec, 5.5 km SE from Morelia; Senguio, and Cerro Grande at 2 km from Tanque de Peña (GBIF, 2018). It is included in a species list from Guatemala but no location data was provided and this record (Kirchmair et al. 2004) was not considered in this assessment.
Many of these historical locations have been lost.
Based on current data, there are 8 subpopilations in Jalisco, 4 in Michoacan, 3 in Oaxaca; with a total 15 known subpopulations in Mexico and one unconfirmed subpopulation in Guatemala.
Considering its EOO of 102,000 km2, we estimate that there are up to 150 potential subpopulations. Given that the mature Quercus forests they inhabit are severely fragmented, and that the size of the fragments are small we assume each population to contain a maximum of 50 mature individuals.
Population Trend: Deteriorating
Saprotrophic and gregarious. It is reported only with hardwood trees, mostly oaks, restricted to old forests. Also growing in soil at base near dead Quercus. The forest composition can vary from pure Quercus, Quercus-Pinus mixed forests, and cloud mountain forest where old Quercus are important components of the community.
Many of the sites where the species is recorded are close to human populations. Four records (probably the same subpopulation) from Senguio, Michoacan from 2008, 2010, 2011 and 2012 disappeared because the site was converted into an agricultural field. Another two populations, 5.5 km SW and 5.5 km NW from La Venta del Astillero (1982, 1986), disappeared due to habitat destruction.
Mature Quercus forests are dissapearing rapidly from Mexico due to logging and changes in land cover to agricultural lands or avocado orchards. Consequently this habitat is declining and severely fragmented.
The habitat of this species are old oak forests or old oak dominated forests. These forests are often surround by large urban areas and are subjected to high anthropogenic pressure. As some subpopulations have disapered due to changes in land cover, protection of known populations is needed. Additionally, logging of large old oaks should be halted in these forests.
Increase sampling effort to confirm distribution. Most collection records of O. mexicanus state “associated with Quercus sp.” without identifying the oak species so better data on association would be informative. A better understanding of the ecology and biology is needed in order to propose more specific conservation plan.
Omphalotus mexicanus is considered to be a toxic species so it is not harvested for culinary or other uses.
Leopoldo Galicia and Leticia Gomez-Mendoza (2010). Temperate Forests and Climate Change in Mexico: from Modelling to Adaptation Strategies, Climate Change and Variability, Suzanne Simard (Ed.), ISBN: 978-953-307-144-2,
Mora VM, Guzmán ,1984. Agaricales poco conocidos en el Estado de Morelos [Agaricales little known in the state of Morelos Mexico]. Boletín de la Sociedad Mexicana de Micología 18: 115–39.
Kirchmair M, Poder R, Huber CG, Miller OK., 2002. Chemotaxonomical and morphological observations in the genus Omphalotus (Omphalotaceae). Persoonia 17 (4): 583–600.
Kirchmair M, Morandell S, Stolz D, Poder R, Christian Sturmbauer C, 2004. Phylogeny of the genus Omphalotus based on nuclear ribosomal DNA-sequences. Mycologia, 96(6), 2004, pp. 1253–1260.
Petersen, RH.; Hughes, KW, 1997. Mating systems in Omphalotus (Paxillaceae, Agaricales). Plant Systematics and Evolution 211(3-4): 217–29.
Luna-Vega I, Alcántara Ayala O, Contreras-Medina RL, Ponce-Vargas A, 2006. Biogeography, current knowledge and conservation of threatened vascular plants characteristic of Mexican temperate forests. Biodiversity and Conservation 15:3773–3799 DOI 10.1007/s10531-005-5401-1