Advances in the knowledge of South African Riella (Sphaerocarpales) and a new endemic species, Riella trigonospora

Cultures of soil sediments collected in June 2012 from saltpans and vleis from five South African localities have revealed two new, geographically distant, populations of the endemic Riella alatospora, confirmed the presence of Riella purpureospora from Blouvlei in the Cape Town area and uncovered a new endemic species, Riella trigonospora. The new species obtained from cultures from five sampled localities is described and illustrated. It is dioicous and characterised by acuminate to rostrate, papillose involucres and by a unique spore morphology. The spores are dark purple, as in R. purpureospora, and have an irregular discontinuous wing at the equatorial plane, which suggests a morphological affinity to R. alatospora. The spores possess a combination of characters that are unique among extant species of Riella, including the triangular spore body with concave sides, a discontinuous equatorial wing, and short blunt spines on the distal face and the expanded parts of the wing at the spore angles. Such peculiar spore morphology is to some extent similar to Heerisporites variabilis, a sporomorph from Upper Miocene deposits of Switzerland and suggests links to Riellaceae from the Mediterranean basin. A lectotype is designated for R. purpureospora and a new description and illustration, incorporating additional characters derived from the cultured plants, are also presented, together with an identification key to the South African species of Riella.