Milesina thailandica, a second rust fungus on an early diverged leptosporangiate fern genus, Lygodium, found in Thailand

Abstract

A new rust fungus was found on Lygodium flexuosum at Doi Suthep-Pui National Park in Chiang Mai Province, Thailand. Puccinia lygodii was the only rust fungus currently known on Lygodium spp. (Lygodioideae, Schizaeaceae, Schizaeales) from southern North America through northern South America. The new fungus produced uredinia linearly between veins, causing yellowish streaks, on the abaxial frond surface. The sori were covered with a layer of thin-walled fungal cells beneath the host epidermis and surrounded by thin-walled paraphyses. The sori did not have a distinct central aperture with ostiolar cells but ruptured irregularly to release urediniospores. Urediniospores were obovoid, obovoid-ellipsoid, or pyriform. The wall was thin, colorless, and completely echinulate. Neither amphispores nor teliospores were observed. The sorus and spore morphology indicated the taxonomic affinity of the fungus to the fern rust genera Hyalopsora and Milesina. A molecular phylogenetic analysis using nuclear large subunit ribosomal DNA sequence revealed that the Lygodium rust fungus was grouped in a paraphyletic Milesina clade. From the putative host preference, morphology, and estimated phylogenetic relationships, it was concluded that the fungus was a new species of Milesina.