Haustoria of microcyclic rust fungi Uromyces ficariae and Puccinia tumida and other gall‐forming species, U. dactylidis (macrocyclic) and P. smyrnii (demicyclic)

Cytological studies involving light and scanning electron microscopy examined the morphology of intracellular hyphae of various gall‐forming species of rust fungi. Uromyces ficariae (microcyclic) and U. dactylidis (macrocyclic, heteroecious) both produced vermiform and largely indeterminate intracellular hyphae typical of M‐haustoria, associated with telial and aecial galls, respectively, on their common host Ranunculus ficaria . Similar M‐haustoria were observed in telial galls of Puccinia tumida (microcyclic) on Conopodium majus , in host tissue affected by nine other microcyclic species and in aecial galls of P. smyrnii (demicyclic, autoecious) on Smyrnium olusatrum . Telia of P. smyrnii , however, infecting photosynthetically active mesophyll without gall formation, produced typical D‐haustoria with determinate growth, a narrow neck region and a bulbous clavate body. Gall formation was associated with hyphal infection of vascular tissue. The relationship between M‐haustoria, vascular infection and gall formation is discussed in relation to the evolution of microcyclic rusts and Tranzschel's law.