The evolutionary ecology of myco‐heterotrophy

Summary Nonphotosynthetic mycorrhizal plants have long attracted the curiosity of botanists and mycologists, and they have been a target for unabated controversy and speculation. In fact, these puzzling plants dominated the very beginnings of the field of mycorrhizal biology. However, only recently has the mycorrhizal biology of this diverse group of plants begun to be systematically unravelled, largely following a landmark Tansley review a decade ago and crucial developments in the field of molecular ecology. Here I explore our knowledge of these evolutionarily and ecologically diverse plant–fungal symbioses, highlighting areas where there has been significant progress. The focus is on what is arguably the best understood example, the monotropoid mycorrhizal symbiosis, and the overarching goal is to lay out the questions that remain to be answered about the biology of myco‐heterotrophy and epiparasitism. Contents Summary 335 I. Introduction 335 II. Monotropa : over 180 years of controversy 337 III. Do all epiparasites evolve from photosynthetic mycorrhizal ancestors? 339 IV. What is unique about the monotrope radiation? 342 V. Potential sources of exceptional myco‐heterotrophy 344 VI. What form of carbon moves from fungus to plant? 344 VII. Mycorrhizas vs reproduction? 345 VIII. What fungal signal triggers symbiotic seed germination? 346 IX. Conclusions 348 Acknowledgements 348 References 348

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