4-HUNDRED-MILLION-YEAR-OLD VESICULAR-ARBUSCULAR MYCORRHIZAE

The discovery of arbuscules in Aglaophyton major, an Early Devonian la nd plant, provides unequivocal evidence that mycorrhizae were establis hed >400 million years ago. Nonseptate hyphae and arbuscules occur in a specialized meristematic region of the cortex that continually provi ded new cells for fungal infection. Arbuscules are morphologically ide ntical to those of living arbuscular mycorrhizae in consisting of a ba sal trunk and repeatedly branched bush-like tuft within the plant cell . Although interpretations of the evolution of mycorrhizal mutualisms continue to be speculative, the existence of arbuscules in the Early D evonian indicates that nutrient transfer mutualism may have been in ex istence when plants invaded the land.