Lichen Photobionts

Photobionts in a lichen get a raw deal in the naming department. The algal or cyanobacterial partner in the relationship may do all the hard work of using light to make glucose but lichens are named after their fungal component This might seem an unfair outcome until one considers that there are c. 15, 000 fungal species described for lichens but only c. 100 photobiont species (1). So its not taxonomic snobbery, its a case of the fungal partner being the more distinguishing of the two. However, although they may not be distinguishing, I do feel that they are rather distinguished. Below are examples of genera of two of the more common photobionts isolated from their respective partners:- Trebouxia (an algae and termed a phycobiont) and Nostoc (a cyanobacteria and termed a cyanobiont). While many lichens have both phyco- and cyanobionts, one dominates and is termed the primary photobiont (2). 90% of lichens contain phycobionts, the remaining 10% having cyanobionts (1).

Trebouxia sp. (centre) isolated from Ramilia fraxinea

Nostoc sp. (chain of cells in centre) isolated from Collema cristatum

References:

1. Lücking et al., 2009. American Journal of Botany 96 pp. 1409-1418
2. Whelan, 2011. Lichens of Ireland pp. 4-5