The myco-heterotrophic Voyria flavescens (Gentianaceae) and its associated fungus

The myco-heterotrophic Gentianaceae Voyria flavescens from the Peruvian Amazon was investigated morphologically and anatomically. Most attention was paid to the subterranean structures and the mycorrhiza. The architecture of the underground organs and the process of root development in particular indicates neoteny. The stellately arranged roots are lacking a pericycle, an endodermis in the conventional meaning, a rhizodermis and a root-cap. All roots emerge exogenously from a so-called ‘rhizoferous axis’. The root-tips show a capacity of exogenous shoot-regeneration. Further it was found that fungal penetration is restricted to dark banded zones of the root’s surface. These zones are the result of a unique mode of apical growth. The associated fungi colonize the entire cortex intracellularly. In the innermost cortical layers the hyphae are longitudinally spreading, whereas they successively degenerate in the outer cortex. In the final phase of disintegration the hyphal coils almost entirely consist of a highly refractive crystalline substance. The mycorrhizal pattern corresponds to a specialized Paris-type vesicular-arbuscular mycorrhiza, lacking both, arbuscles and vesicles. Due to auxiliary cells, being connected to root invading hyphae, an associated fungus could be identified as most likely being a member of Gigasporaceae (Glomeromycota).