Growth dynamics in Cladonia grayi

Abstract

The erect secondary thallus (podetium) of the lichen Cladonia grayi develops in distinct stages that can be traced to the development of its fungal meristem tissue. In early ontogeny, while the contiguous meristem grows unilaterally both outward and vertically, the gross morphology of the podetium resembles other cup-forming species. In later ontogeny, when the divided meristem grows vertically, the podetium forms a subtly articulated spiral. The spiral growth form is most apparent in branching proliferations that grow along the cup margin. The meristem tissue at the apex of these proliferations is curved, maturing sequentially in a spiral pattern. The proliferations curve in a spiral around the vertical axis of the podetium. Apothecia at the apex of proliferations curve in a similar manner. Evidence for spiral growth along the cup margin can also be inferred from the sequential development of pycnidia that emerge from it. Similar to early land plants, the growth dynamics of C. grayi may represent an evolutionary advance from an orthotropous growth pattern to a branched, photosynthetic thallus.

Key Words:

• developmental morphology
• lichen architecture
• thallus morphogenesis
• evolution