Lactarius acatlanensis should be listed as Endangered under the criteria B2ab(ii,iii). This is an ectomycorrhizal species associated with Fagus grandifolia var. mexicana forests, which has been extremely reduced due to anthropogenic impacts. The known area of occupancy is less than 1.275 km2, with a maximum potential area of occupancy 4.25 km2 that corresponds to the actual remaining patches of its host. There are only two known populations and the maximum number of populations is less than ten. The remaining forests of the Mexican Fagus grandifolia var. mexicana are isolated and fragmented, covering areas smaller than 42 ha each. All the surrounding areas of these forests have been changed entirely to cropping and urban lands and L. acatlanensis populations will decline due to deforestation, pollution, and edge effects.

Lactarius acatlanensis has a centrally depressed pileus, plane to infundibuliform, loosely fibrillose to strigose at the center and margin, hygrophanous, zonate, and the pileus surface is cream-yellowish. The lamellae are decurrent and pale ochraceous-cream to yellow colored. The latex is milky to whey-like, staining white paper yellow. Lactarius pseudodelicatus is a similar species but has pale yellow coloration and faintly zonate pileus, a stipe with large, pale honey-colored spots, burning taste, and latex that does not change in color. Also similar is L. luteocanus which has a latex that stains white paper yellow, is azonate to faintly zonate, viscid, dull white to pinkish-buff or cinnamon-buff pileus. Other species sharing pubescent pileus surfaces that should be compared with L. acatlanensis are L. tesquorum and L. mairei (Bandala et al., 2016).

Lactarius acatlanensis is an ectomycorrhizal species only known to develop in Acatlan Volcano and Xalapa, both localities in Veracruz state (eastern Mexico). Besides these localities, there has been reported from nowhere else. Lactarius acatlanensis grows in relicts of subtropical cloud forests dominated by its host Fagus grandifolia var. mexicana, an endemic species of Mexico and very threatened due to agriculture, cattle raising, deforestation and other changes in land use. Lactarius acatlanensis should be protected because of the limited distribution of its ectomycorrhizal host and the pressures of its habitat.

Lactarius acatlanensis is limited to Veracruz state in Southeast Mexico. There are only two known subpopulations: one subpopulation in Acatlan Volcano, in the eastern Sierra Madre Oriental, Veracruz; and another one located 2 km southwest of Xalapa city, near the Coapexpan River (Bandala et al., 2016). Lactarius acatlanensis is ectomycorrhizal limited to its host Fagus grandifolia var. mexicana distribution, an endemic tree from Mexico, whose populations have been dramatically reduced due to land use changes to introduce cropping and cattle. According to Rodríguez-Ramírez et al. (2013) of 14 original stands dominated by F. grandifolia var. mexicana over the states of Nuevo Leon and Tamaulipas in Northeastern Mexico, Hidalgo and in center Veracruz in the East of Mexico, only 11 currently persist with a total area of 4.25 km2.

Known subpopulations of L. acatlanensis are limited to Veracruz, Mexico exclusively. There is only one population in Acatlan Volcano, where it has been found 23 times in the course of eight years since 2004. The remaining data of the presence of this species (4 observations) come from a patch of approximately 2 ha, part of private property located 2 km southwest of the city of Xalapa (Bandala et al., 2016). Lactarius acatlanensis is restricted to Fagus grandifolia var. mexicana forests, whose populations have been dramatically reduced due to land use changes to introduce cropping and cattle. According to Rodríguez-Ramírez et al. (2013) of 14 original stands dominated by F. grandifolia var. mexicana over the states of Nuevo Leon and Tamaulipas in Northeastern Mexico, Hidalgo and in center Veracruz in the East of Mexico, only 11 currently persist, with a total area of 144 ha. Lactarius acatlanensis has been reported only in one of these sites, the Acatlan Volcano. The other locality of this species is a small patch immersed in Xalapa city under extremely anthropogenic pressures due to the urban surrounding lands.
The known distribution of the species is robust since we have tested the DNA barcode of the type specimen against a soil fungi database from Mexico (unpublished data). Thanks to this, we discarded the association of L. acatlanensis with other Fagaceae forests (Quercus spp); so it’s highly probable that L. acatlanensis distributes exclusively in F. grandifolia var. mexicana forests.

Lactarius acatlanensis is gregarious. It has been collected only in Fagus grandifolia var. mexicana dominated forests (Williams-Linera et al., 2000), with some other tree elements like Quercus laurina and Quercus sp. in Acatlan Volcano according to Bandala et al. (2016). This species is ectomycorrhizal with F. grandifolia var. mexicana (Montoya et al., 2017). Testing against a soil fungi database from Mexico (unpublished data) we have discarded the distribution of L. acatlanensis in other Fagaceae forests (Quercus for example); so it’s highly probable that L. acatlanensis form ectomycorrhizal associations exclusively with F. grandifolia var. mexicana.

The subtropical cloud forests, particularly those dominated by Fagus grandifolia var. mexicana, have suffered fragmentation and are being greatly reduced due to different types of disturbances including climatic change, illegal timber extraction, and land use changes. Also, local residents collect the seeds of the Mexican Fagus to eat and/or sell locally, which could decrease the natural regeneration of these trees (Rodríguez-Ramirez et al., 2013). Nowadays, according to Rodríguez-Ramirez et al. (2013) the Mexican Fagus persists only in patches. For example, all lands that surround Acatlan Volcano has been dramatically changed to cropping and cattle, increasing the isolation of F. grandifolia var. mexicana forests, which is the only known viable population of Lactarius acatlanensis; the other locality where this species has been recorded is a relict forest garden immersed among urban territories, with pollution and edge effects as the main threats additional to the previously referred.

By now Acatlan Volcano territory is not protected by any law. It would be necessary to formally protect it in order to preserve one of the scarce patches of relict stands of Fagus grandifolia var. mexicana at this latitude (Bandala et al., 2016), which represents a refuge for fungi like L. acatlanensis. Fagus grandifolia var. mexicana is currently classified as in risk of extinction by “Norma Oficial Mexicana NOM-059-Semarnat-2010”, which lists the Mexican species of animals, plants and fungi under protection, due to mainly uncontrolled human activity such as changes in land use and illegal logging. According to Rodríguez-Ramírez et al. (2013) there is only one population of Fagus grandifolia var. mexicana considered in National Park territories (in El Cielo, Biosphere Reserve, Tamaulipas, Mexico).

One of the main needs is to increase the sampling effort, particularly in other patches of Fagus grandifolia var. mexicana to elucidate if L. acatlanensis known distribution is constrained by the absence of records, or if it represents the natural species distribution range. Some studies regarding the actual distribution of Fagus grandifolia var. mexicana populations indicate that most of them are currently isolated from each other, and some others already have disappeared (Rodríguez-Ramírez et al., 2013), so to investigate the genetic structure of Lactarius acatlanensis populations in those areas is needed, to detect any geographical isolation due to habitat fragmentation.

There are not reports about edibility or use of this species.

Bandala, V. M., Montoya, L., & Ramos, A. (2016). Two new Lactarius species from a subtropical cloud forest in eastern Mexico. Mycologia, 108(5), 967-980.

Montoya, L., Bandala, V. M., Ramos, A., & Garay-Serrano, E. (2017). The ectomycorrhizae of Lactarius rimosellus and Lactarius acatlanensis with the endangered Fagus grandifolia var. mexicana. Symbiosis, 73(2), 135-144.

Rodríguez-Ramírez, E. C., Sánchez-González, A., & Ángeles-Pérez, G. (2013). Current distribution and coverage of Mexican beech forests Fagus grandifolia subsp. mexicana in Mexico. Endangered Species Research, 20(3), 205-216.

Williams‐Linera, G., Devall, M. S., & Alvarez‐Aquino, C. (2000). A relict population of Fagus grandifolia var. mexicana at the Acatlan Volcano, Mexico: structure, litterfall, phenology and dendroecology. Journal of Biogeography, 27(6), 1297-1309.