Flies of the Colocasiomyia toshiokai species group depend exclusively on inflorescences/infructescences of the aroid tribe Homalomeneae. The taxonomy and reproductive biology of this group is reviewed on the basis of data and samples collected from Southeast Asia. The species boundaries are determined by combining morphological analyses and molecular species delimitation based on sequences of the mitochondrial COI (cytochrome c oxidase subunit I) gene. For the phylogenetic classification within this species group, a cladistic analysis of all the member species is conducted based on 29 parsimony-informative, morphological characters. As a result, six species are recognised within the toshiokai group, including one new species, viz. C. toshiokai, C. xanthogaster, C. nigricauda, C. erythrocephala, C. heterodonta and C. rostrata sp. n. Various host plants are utilised by these species in different combinations at different localities: Some host plants are monopolized by a single species, while others are shared by two or three species. C. xanthogaster and C. heterodonta cohabit on the same host plant in West Java, breeding on spatially different parts of the spadix. There is a close synchrony between flower-visiting behaviour of flies and flowering events of host plants, which indicate an intimate pollination mutualism.
The fourth part of a revision of linear-leaved species of the genus Potamogeton in the Czech Republic is given, dealing with P. pusillus s.l. and P. trichoides. The appropriate taxonomic concept and species delimitation within P. pusillus s.l. are discussed. Because of still unresolved taxonomic difficulties and high percentage of specimens that cannot be assigned to one of the two traditionally distinguished species, P. pusillus s. str. (syn. P. panormitanus) and P. berchtoldii, the broader concept of P. pusillus s.l. has tentatively been adopted in this revision. This species complex is widespread in the Czech Republic, absent only in relatively small areas of the highest elevations and the driest areas without suitable biotopes. P. pusillus s.l. is the commonest taxon of Potamogeton in standing waters. P. trichoides, a well defined species distinguished by several morphological characters, occurs scattered mainly in S, C and E Bohemia and S and C Moravia, with most localities concentrated in S Bohemia. It is considered as strongly threatened species of the Czech flora. Species descriptions, relevant synonyms, illustrations, a list of specimens examined and distribution maps are provided for both species. P. rutilus was once reported from the Czech Republic in error. No specimen from this country has been found in herbaria.