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Genera assigned to the Jahnulales are morphologically diverse, especially in ascospores equipped with or without appendages, sheaths or apical caps. They are predominantly freshwater fungi occurring on woody substrata, with Manglicola guatemalensis, Xylomyces chlamydosporus and X. rhizophorae the only species known from marine habitats. The order Jahnulales with 4 teleomorphic genera: Jahnula (15 species), Aliquandostipite (5), Megalohypha (1), Manglicola (2) and the anamorphic genera Brachiosphaera (2), Speiropsis (9), Xylomyces (8), amounting to a total of 42 species, is reviewed and nomenclatural changes are proposed. Twenty species are treated at the molecular level, with 94 sequences, 13 of which are newly generated for this review. Three species are rejected (Speiropsis irregularis, Xylomyces aquaticus, X. elegans) while the phylogenetic placement of 6 Xylomyces, 7 Speiropsis, 1 Brachiosphaera and 1 Manglicola require molecular data to confirm their placement in the order. Sequences are derived from ex-holotype isolates and new collections made in Thailand. Most taxa are included in the family Aliquandostipitaceae and a new family Manglicolaceae is erected for the marine ascomycete Manglicola guatemalensis with its large ascomata (1,100–1,750 × 290–640 μm), wide ostioles and ascospores that are fusiform, unequally one-septate with the apical cell larger than the turbinate basal cell and bear apical gelatinous appendages. The genus Jahnula is polyphyletic grouping in three clades with J. aquatica, J. granulosa, J. rostrata, J. potamophila and Megalohypha aqua-dulces in the Jahnula sensu stricto clade. No taxonomical changes are proposed for Jahnula species not grouping in the Jahnula sensu stricto clade, until further species are isolated and sequenced.

An undescribed ascomycete similar to species in the Aliquandostipitaceae (Jahnulales, Dothideomycetes) was collected from submerged wood in a freshwater swamp in Big Cypress National Preserve, Florida. The characteristic features of the new species are as follows: (i) ascomata are small, sessile, light brown, globose to subglobose, papillate, and anchored to the substrate by wide, brown, septate and subtending hyphae; peridial wall is composed of 1 to 2 layers of large, angular cells with large lumens; (ii) asci are ovoid to broadly clavate, and fissitunicate; (iii) ascospores are one-septate, fusiform, multiguttulate, pale brown, surrounded by a fusiform gelatinous sheath, and equipped with numerous filamentous appendages around the midseptum. The new fungus is most similar to Aliquandostipite crystallinus, from which it differs in overall smaller size and morphology. This new fungus is described and illustrated herein as A. minuta.

A new order is introduced ( Jahnulales ) to accommodate ascomycetes with stalked/sessile and dimorphic ascomata, hyphal stalk cells that are ca 40 μm wide, and ascospores that are unequally 2-celled with or without various types of appendages or sheaths. The order includes a single family, the Aliquandostipitaceae , and has affinities with the Pleosporales within the Dothideomycetes. Studies on freshwater ascomycetes in Egypt and Thailand yielded one new genus Patescospora , and Jahnula siamensiae sp. nov., and the new combination J. sunyatsenii (syn. Aliquandostipite sunyatsenii ) is made based on molecular results.

In two short surveys of lignicolous, fruitbody-forming ascomycetes in Thailand and southern China, six species were found, of which five were new to science. Two fungi with affinity to the Dothideomycetes, one from Thailand and one from China, are described here in the new genus Aliquandostipite and included in the new family Aliquandostipitaceae. Aliquandostipite khaoyaiensiswas found in a tropical rain forest in Thailand and A. sunyatsenii in a small stream in southern China. Both new species are closely related based on morphological and molecular characteristics and with uncertain affinity to other taxa of the Euascomycetes based on phylogenetic analyses of SSU rDNA sequences. The distinguishing features of the new species are the presence of both sessile and stalked ascomata side by side on the substratum and the widest hyphae known from ascomycetes.