Primary tissue and the structure of the podetium in Cladonia

Abstract

The podetium is an erect, tubular, lichenized structure that constitutes the secondary thallus (thallus verticalis) in the lichen genus Cladonia. The primary tissue, an assemblage of meristematic cells, is present from the inception of the podetium through maturity. Assuming that it is homologous throughout, primary tissue can be compared among species of Cladonia to clarify taxonomic relationships. The current infrageneric classification within the genus is in part artificial because the characters upon which the taxa are based are formed in various ways. Some examples are: 1) Species in the informal Furcatae group are placed within sections Perviae or Cladonia, but they differ from the species in either section on the basis of the configuration and ontogeny of their primary tissue. 2) Certain scyphus-forming species in sections Cladonia and Cocciferae produce proliferations that resemble species in section Perviae. 3) Some scyphusforming species in section Cladonia produce proliferations that resemble species in the Furcatae group.

Key Words:

• Cladonia
• classification
• development
• lichen
• meristem
• morphology
• podetia
• systematics