[5] The asexual stage (anamorph) of the fungus was first described by the German botanist and mycologist Felix von Thümen in 1880 as Ascochyta clematidina.
Based on new scientific insights into the differences in spore formation between species,[6] it was reclassified as Phoma clematidina by the Dutch mycologist Gerhard Boerema in 1978.
[1] Genetic sequencing has suggested that Calophoma clematidina is heterothallic which means that two compatible strains (mating types) of the fungus would need to come together under the right environmental conditions to produce a sexual stage (teleomorph).
[9][10] Unlike Calophoma clematidina, the two closely related Didymella species (and their anamorphs) have not been found on large-flowered Clematis varieties.
[3][4] Within a nursery or garden, the fungus is mainly spread through splash dispersal of its asexual spores (conidia) which are formed in bulbous fruiting bodies called pycnidia.
Movement of infected plant material forms an important method of spread to previously unaffected nurseries or gardens.
In addition, it forms thick-walled resting spores (chlamydospores) which increase its survival in plant debris and soil during unfavourable conditions.
However, although wounding may aid infection, scientific trials have shown that, in susceptible Clematis varieties, the fungus can cause extensive leaf spotting and wilt without any previous damage to plant tissues.
Scientific trials have shown that large-flowered varieties are especially susceptible to disease caused by Calophoma clematidina in line with their vulnerability to wilt observed in practice.
[9] However, further genetic studies of the isolates used in those trials have revealed that the fungus released as biocontrol agent had been misidentified and was not Calophoma clematidina, which thus far has never been found on Clematis vitalba.