The Lichen Photobiont: What Can It Tell Us about Lichen Systematics?

Our improved ability to isolate, culture, and identify photobionts has given us new insights into how they can be used in lichen systematics. Identification ofdifferent types ofphotobionts isolated from a wide variety of lichens has shown that there is not a well-defined pattern between the mycobiont and its corresponding photobiont. It is unlikely that taxonomists can find much value in the types of photobionts that occur in lichens, at least at the species level. Although photobionts do not have a determining role in the kinds of thalli produced, they are essentialfor thallus formation. A mycobiont cannot produce a thallus alone. Whateverfactor thephotobiont produces that stimulates thallus morphogenesis must be a general one, i.e., something that can turn on the genes of different