Looks can be deceiving: the deceptive milkcaps (Lactifluus, Russulaceae) exhibit low morphological variance but harbour high genetic diversity

Abstract

The ectomycorrhizal genus Lactifluus is known to contain many species complexes, consisting of morphologically very similar species, which can be considered cryptic or pseudocryptic. In this paper, a thorough molecular study is performed of the clade around Lactifluus deceptivus (originally described by Peck from North America) or the deceptive milkcaps. Even though most collections were identified as L. deceptivus, the clade is shown to contain at least 15 species, distributed across Asia and America, indicating that the L. deceptivus clade represents a species complex. These species are morphologically very similar and are characterized by a tomentose pileus with thinwalled hyphae and a velvety stipe with thick-walled hyphae. An ITS1 sequence was obtained through Illumina sequencing for the lectotype of L. deceptivus, dating from 1885, revealing which clade represents the true L. deceptivus. In addition, it is shown that three other described species also belong to the L. deceptivus clade: L. arcuatus, L. caeruleitinctus and L. mordax, and molecularly confirmed that L. tomentoso-marginatus represents a synonym of L. deceptivus. Furthermore, two new Neotropical species are described: Lactifluus hallingii and L. domingensis.

Lactifluus (Russulaceae) diversity in Central America and the Caribbean: melting pot between realms

“…Albati , but occurs in Central America, L. domingensis has slightly higher spore ornamentation (up to 1.7 μm), somewhat shorter basidia ((42–)43– 53 –63.5 × 9.5– 12.5 –15.5 μm), somewhat differently shaped macrocystidia (i.e., more often a mucronate or moniliform apex, more rarely with a rounded or tapering apex) and a loosely arranged cutis to trichoderm as a pileipellis. In addition, L. hallingii is associated with Quercus , while L. domingensis is associated with Pinus occidentalis ( Delgat et al 2019 ).…”

“…5 -12.5 -15.5 µm), somewhat differently shaped macrocystidia (i.e., more often a mucronate or moniliform apex, more rarely with a rounded or tapering apex) and a loosely arranged cutis to trichoderm as a pileipellis. In addition, L. hallingii is associated with Quercus, while L. domingensis is associated with Pinus occidentalis (Delgat et al 2019). Delgat & De Wilde,IMA Fungus 10 (14): 10.…”

“…However, these species are in need of a thorough molecular study. Other areas in Central America and the Caribbean have been studied less intensively, yielding only three species of Lactifluus described from the Greater Antilles, one Lactifluus species from Central America and four species from southern Mexico ( Singer 1973 , Montoya et al 1996 , Montoya et al 2012 , Miller et al 2000 , Montoya & Bandala 2004 , Crous et al 2019 , Delgat et al 2019 ).…”

From White to Black, from Darkness to Light: Species Delimitation and UNITE Species Hypothesis Testing in the Russula Albonigra Species Complex.

“…This is a phenomenon that is widely distributed within the Russulaceae family, especially in the genus Lacti uus (Pers.) Roussel (Stubbe et al 2010, Van de Putte et al 2010, Van de Putte 2012, De Crop et al 2014, Van de Putte et al 2016, Delgat et al 2017, De Lange et al 2018, Delgat et al 2019, but also within the genus Russula (Adamčík et al 2016a, Adamčík et al 2016b. A multi-locus phylogeny resulting in a strong support of the European species within the R. albonigra complex, stimulated the detailed search for morphological differences between the species.…”

“…Due to the low morphological variability we could consider the species within the R. albonigra complex pseudocryptic species (i.e. species with a morphological resemblance that seem indistinguishable at rst, but can be distinguished when using the appropriate characters (Delgat et al 2019)). This is a phenomenon that is widely distributed within the Russulaceae family, especially in the genus Lacti uus (Pers.)…”