Developmental biology of lichens.

Lichen-forming fungi are a large, taxonomically diverse group of nutritional specialists which acquire fixed carbon from a population of minute green algal or cyanobacterial cells. Mycobionts of foliose or fruticose lichens differ from the rest of the fungi by expressing morphologically and anatomically complex symbiotic phenotypes. The extracellularly located photobiont cell population of these macrolichens is housed and controlled by the quantitatively predominant fungal partner which competes for space above ground, secures adequate illumination and facilitates gas exchange. This review summarizes data on the ontogeny, functional morphology, growth patterns and internal thalline differentiation of macrolichens. Contents Summary 659 I. Introduction 659 II. Establishment of the lichen symbiosis 662 III. Growth and cell turnover 669 IV. Outlook 674 Acknowledgements 674 References 674.