The traditional classification of picoas (Picoa Vittad.) was based on the original descriptions of its two historic species: Vittadini defined Picoa juniperi by its warted surface, while Patouillard described Phaeangium lefebvrei —later combined as Picoa lefebvrei— by a hairy, wartless peridium. To this was later added a criterion widely assumed in the popular literature, namely that spores would be smooth in P. juniperi and warty in P. lefebvrei. However, recent phylogenetic studies have shown that these classic morphological characters do not reliably distinguish the species within the genus.
The first such study, based on ribosomal DNA sequencing —ITS and LSU— and the RPB2 gene from 70 specimens collected across the Mediterranean basin (Zitouni-Haouar et al., 2015, PLOS ONE 10(9): e0138513), revealed that the genus comprises at least six well-differentiated genetic lineages. This study further showed that spore ornamentation is not a reliable diagnostic character, since it may depend, at least in some lineages, on the maturity of the specimen. A second, more recent study (Alvarado, Paz, Lavoise & Van Vooren, 2026, Journal of Fungi 12(2): 84) has considerably expanded the genetic and morphological study of the genus and has proposed recognising at least 19 species within Picoa, 17 of them new to science, grouped into five sections, while also pointing out the existence of further lineages not yet formally described that probably represent additional species.
Thanks to genetic sequencing of our own material, we have been able to identify several of these lineages among the specimens we have collected over the years. However, we do not intend to provide a formal taxonomic description of these species here, since the number of specimens available to us is not sufficient to precisely delimit their morphological variability, especially in relation to the degree of maturity of each specimen. A further, no less important difficulty is that several Picoa species of very similar outward appearance can coexist at the same collecting site —in our case, up to three different species collected together at a single point, which we were unable to tell apart in the field. For this reason, we do not consider any specific determination based solely on morphological characters, whether macroscopic or microscopic, to be reliable, and we believe that only genetic sequencing allows each specimen to be confidently assigned to its corresponding species.
In our experience, characters such as the degree of truncation, flattening or umbonation of the peridial warts show considerable variability and do not allow the species of Picoa to be reliably separated. These features can be useful for describing the appearance of a particular specimen, but should not be interpreted as reliable diagnostic characters unless supported by molecular data.
Something similar happens with spore ornamentation. In our material, observed under the light microscope, the ascospores appear hyaline, spherical to subglobose or slightly ellipsoidal in outline, with an apparently smooth surface or, at most, finely granulose. Although some recent authors have described more varied spore ornamentation in Picoa, we believe this character should be interpreted with great caution, especially under the light microscope, since it can be affected by the degree of maturity, focus, mounting technique and the perisporium itself. For this reason, we likewise do not regard it as a reliable criterion for species separation when it is not supported by genetic sequencing.
Below we present some of these picoas, all identified from our own sequenced material, together with photographs and locality data. These data correspond to our own collections and are not intended to formally replace or extend the published distribution of each species; readers wishing to learn more about their taxonomy are referred to the two scientific papers cited above.
Overall, picoas have a peridium ranging from brown to black, and a white gleba that remains so even in fully mature specimens. In young specimens, reddish-brown or ochre mycelial hairs are frequently observed. The asci, quickly evanescent, are subglobose and pedicellate, containing 4-8 globose to broadly ellipsoidal, hyaline ascospores, apparently smooth or weakly ornamented under the light microscope.
In our own collections, and in the mycorrhizae we have studied, picoas always appear associated with the roots of Helianthemum spp. Although some papers cite collections made under or in the presence of Cistus, Tuberaria, Quercus, Pinus or other plants, the presence of these species in the habitat should not be confused with a confirmed mycorrhizal association. Annual Helianthemum plants are often very small and can easily go unnoticed.
Preliminary observations from ongoing studies on the mycorrhizal colonisation of Helianthemum by Picoa species suggest that this genus may have a notably high mycorrhization capacity, which would help explain its frequent occurrence even in areas where no Terfezia fruiting bodies have been detected.
Picoa vazqueziae
Ascoma subglobose, fairly regular, 1-3 cm in diameter. Peridium black, covered with polygonal, flattened and frequently umbonate warts, which in some specimens can reach up to 4 mm in width (see detail of the warts). Externally, these picoas closely resemble summer truffles. Gleba white, with white veins enclosing the fertile tissue. Smell sweetish, of coconut. Pleasant taste. Microscopy: asci subglobose, with 6-8 hyaline ascospores, globose to broadly ellipsoidal, with a large guttule, measuring 22-28 (32) x 22-25 (28) µm (Q=1.00-1.16). These ascospores are smooth, and only when mature do they appear finely granulose under the light microscope.
Localities: Casas de Lázaro and Alcaraz (Albacete)
Picoa truncata
Ascoma subglobose, 1-3 cm in diameter. Peridium verrucose, brown when young and covered with a felt of ochre hairs; at maturity it turns black, with more pronounced warts. Gleba white. These two picoas, apparently so different, were sequenced precisely to confirm that they belonged to the same species. Collecting several picoas at the same site does not imply that they belong to the same species: on occasion we have even collected up to three different Picoa species coinciding in time and place within the same site. Only sequencing allows us to ensure the exact identification of each species.
Localities: Balazote, Chinchilla de Monte-Aragón, Pozuelo (Albacete). Espinardo, Corvera, Águilas (Murcia)
Picoa rodensis
Ascoma subglobose, 2-3 cm in diameter. Peridium black or very dark brown, with strongly pronounced warts. Gleba white.
Localities: La Roda (Albacete). Zarzadilla (Murcia)
Picoa microspora
Ascoma subglobose to irregularly lobed, 2-3 cm in diameter. Peridium brown to dark brown, with low warts, 1-1.5 mm wide. Young specimens covered with a hairy-looking ochre tomentum, which tends to disappear with maturation or through friction with the substrate. Gleba white. Asci mostly with eight spores. Ascospores not measured. Growing in association with H. canariense. Our Canary Island specimens represent, as far as we know, the first molecular record of this species outside the eastern Mediterranean and North Africa, where it had so far only been known from Egypt, Cyprus and Tunisia.
Localities: Teguise (Lanzarote). Tenerife.
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Antonio Rodríguez trufamania@gmail.com antonio@trufamania.com ORCID iD: 0000-0002-0708-7773 |