Rhizines occasionally occur in the genus Hypogymnia (Parmeliaceae, Ascomycota)

The genus Hypogymnia is morphologically characterized by swollen lobes, a hollow medulla, perforations in the lower surface, and the absence of rhizines. In our studies on Hypogymnia spp. we found rhizines and hapters were occasionally present on the lower surface of 35 species. Morphology and anatomy of the appendage-organs were studied using dissecting, compound, and scanning electron microscopy and compared with rhizines found in the related genus Arctoparmelia. Two types of rhizinelike structures were found in Hypogymnia: slender and elongated rhizines, and thick and short hapters, both of which were few in number and sparsely distributed on the lower surface. There are no obvious differences in the morphology of rhizines between Arctoparmelia and Hypogymnia, except that rhizines are abundant in Arctoparmelia. Within Parmeliaceae, Hypogymnia belongs to the hypogymnioid clade together with the genera Arctoparmelia, Brodoa, and Pseudevernia, most of which are considered to lack rhizines. The occurrence of rhizines in Hypogymnia is consistent with the placement of Arctoparmelia in the hypogymnioid clade based on molecular data.