The enigma of the Diporotheca palynomorph

In the Quaternary palynological literature, the name Diporotheca rhizophila has come to be applied for fungal spores labelled in the Hugo de Vries-Laboratory (HdV) in Amsterdam (The Netherlands) as Type HdV-143. The widespread occurrence of this taxon in palynological preparations was difficult to understand as the species is definitely known only from Solanum species in Washington State in the USA. Comparison of spores found in palaeoecological and forensic samples with those of the original material (holotype) of D. rhizophila established that the name had been misapplied. Type HdV-143 is distinguished from the holotype by the shape, size, and ornamentation of the ascospores. The spores in the palaeoecological material are navicular to fusiform, and not oval when mature. They develop robust, dark brown, anastomosed ridges from an early stage, and are much longer, measuring 44–59 μm and not 25–37 μm in length. Similarities in spore structure and development indicate that both can be accommodated in the same genus, but as different species. The specimens from palynological preparations are described here as D. webbiae sp. nov. Circumstantial evidence, gained from palaeoecological analysis, suggests that the new species may be associated with the fern genus Thelypteris, and today occurs most commonly in wet Alnus carr. Similar spores have been reported from the pre-Quaternary fossil record under the generic name Striadiporites