Morphological evaluation of peridial wall, ascus and ascospore characteristics in the delineation of genera with unfurling ascospore appendages (halosphaeriaceae)

Abstract

In the Halosphaeriaceae, taxa with unfurling ascospore appendages and related species constitute 61 species (in 21 genera). Recent phylogenetic analyses of the rRNA genes have advanced our knowledge on the relationships between genera in the family, especially the group with unfurling ascospore appendages. However, many new genera resulting from these studies lack distinctive morphological characteristics from closely related taxa. In this chapter, peridial wall layers of the ascomata and morphology of asci and ascospores are re-examined to determine if these structures offer useful information for the delineation of genera. In particular, shape parameters (aspect ratio, convexity, elongation, shape factor, sphericity, area, perimeter, diameter max, diameter mean and diameter min) of ascospores were calculated to determine if these parameters can provide extra characters for the delineation of taxa. Results suggest that peridial wall structure alone is insufficient to separate genera in the Halosphaeriaceae. Shape parameters of ascospores can provide additional characters but more taxa are required to test their efficacy. Ascus shape and length of stalk are further characters that should be calculated for taxonomical consideration. Morphology of the ascomatal wall and shape of asci and ascospores in genera with unfurling ascospore appendages in the Halosphaeriaceae are partially concordant with their phylogeny, suggesting a more thorough examination of these characters for the delineation of taxa in the family.