A new corticolous species of Mycena sect. Viscipelles (Basidiomycota: Agaricales) from the bark of a Living American elm tree in Texas, U.S.A.

A Mycena species new to science was obtained from moist chamber cultures of trunk bark of a living American elm tree (Ulmus americana) located in the Fort Worth Botanic Garden, Tarrant County, Texas. This discovery was part of an ongoing study of corticolous myxomycetes on larger American elm trees occurring in Fort Worth nature parks. More than 15 American elm trees were sampled for trunk bark but only a single tree yielded Mycena basidiomes. Collections of bark began in the summer of 2017 and continued until the beginning of 2020. Bark samples from the north, south and west side of the tree yielded fruit bodies of the mushroom in moist chamber culture. No fruit bodies were observed in nature nor were early formation stages on the underside of the bark. Crystals previously described in another study were present on the bark surfaces, edges, and undersides. Habit and morphological development were photographed using light microscopy applying multifocal imaging and computer stacking to increase depth of field. Basidiome development was observed and photographed from the earliest primordial beginning stage, the button stage, intermediate stage and the final emerging stalk elongation and mature cap formation stage. Mature mushroom development took from 9 to 21 days after wetting the bark in moist chamber cultures. Scanning electron microscopy was used to illustrate development of the button stage, emerging stalk and pileus stage, and the fully mature pileus, lamellae, and pseudocollarium. Morphological features and DNA sequence data confirmed that this Mycena species was undescribed and distinct from other Mycena taxa. Morphological features suggest placement of the novel taxon in Mycena sect. Viscipelles, distinct from other members based on morphological characters and phylogenetic analysis.