Mallomonas imperatoria (Chrysophyceae, Synurales)—a new taxon from the tropics

This study investigates the <i>Mallomonas adamas</i> species complex in a tropical region using electron microscopy and molecular phylogeny. Analysis of four algal cultures from Vietnam, supplemented by data from two cultures from Europe and one from Australia, all belonging to the <i>M. adamas</i> morphotype, revealed two distinct clades in phylogenetic trees based on SSU rDNA + <i>rbcL</i> cpDNA and ITS1-5.8S-ITS2 rDNA sequences. Based on these results, a new species, <i>Mallomonas imperatoria</i> <b>sp. nov.</b>, is described. <i>Mallomonas imperatoria</i> was found in 22 localities across nine provinces in Vietnam and is also known from Malaysia. This species generally prefers acidic water bodies, including those that are humic-stained, with low mineralization. Thus, findings of this taxon are not very frequent, but it cannot be classified as rare in the tropical region.