The arachiform vacuolar body: an overlooked shared character in the ascospores of a large monophyletic group within Parmeliaceae (Xanthoparmelia clade, Lecanorales)

Sections of apothecia were used to study the internal morphology of ascospores in the largest monophyletic clade within Parmeliaceae composed of Xanthoparmelia and related genera. The results were compared with fertile representative species of most other parmelioid clades. All the Xanthoparmelia species had spores with a single smooth vacuole, which was peanut-shaped, with different degrees of constriction in the equatorial plane. This differs from the ellipsoid vacuole of other parmelioids. In the Xanthoparmelia clade, sexual reproduction seems much more common than in other parmelioids. Thus, we suggest that the presence of this unique spore morphology might contribute to the evolutionary success of this monophyletic group. Further, the discovery of this useful ascospore character demonstrates that detailed ascospore morphological studies significantly enhance molecular phylogenetic analyses. Ascospore features may be more taxonomically significant in Parmeliaceae than hitherto considered.