Variation and variability in Cladonia section Perviae

Abstract

The lichenized podetia in the species of Cladonia section Perviae are characterized by variable openings that occur both apically and at axils of branches. The podetia and their openings are variable within species but they are initially formed in distinct patterns. Unique patterns of growth can be distinguished among the species in early ontogeny at the level of the meristematic tissue, which is purely fungal. The morphology of the mature podetium in many Cladoniaceae can be traced to patterns of early ontogeny. While openings in very young growing parts of podetia in species in section Perviae are influenced by the meristem plan, the appearance of mature podetia is strongly influenced by relative growth rates and external factors. The formation of pycnidia from meristematic tissue is similar to the development of branches in certain species, and may provide the morphological basis for determining evolutionary pathways in the genus Cladonia. For example, trichotomous and polytomous branching may have been ancestral to dichotomous branching, which in turn gave rise to other, asymmetrical branching systems.

Key Words:

• Cladoniaceae
• lichens
• podetia
• systematics