A new species of Tetradesmus (Chlorophyceae, Chlorophyta) isolated from desert soil crust habitats in southwestern North America Elizaveta F. Terlova 1* & Louise A. Lewis 1 Abstract. A new species of Tetradesmus (Tetradesmus adustus) is described from desert soils of southwestern North America. The identifcation is based on phylogenetic analysis of data from nuclear (ITS2 rDNA) and plastid (rbcL, tufA) barcode markers. This newly described species represents the ffth cryptic species of arid-adapted algae in Scenedes- maceae. A re-analysis of published sequences attributed to desert Tetradesmus in the context of our newly obtained data reiterates the importance of robust phylogenetic analysis in identifcation of cryptic taxa, such as species of Tetradesmus. Key words: DNA barcoding, rbcL, ITS, tufA, desert algae, green algae Introduction Microbiotic crusts are complex communities of soil microorganisms and cryptogams that occur in arid and semi-arid habitats. Prokaryotic and eukaryotic members of microbiotic crusts act as important “ecosystem engi- neers” by powering nutrient cycles, preventing erosion and enhancing water holding capacity in desert soils, as well as infuencing the composition of plant communities (Evans & Johansen 1999; Belnap & Lange 2001; Song et al. 2017). Early surveys of algae species composition in desert crusts revealed only a small number of species, owing to the simple morphology of many soil algae and identifcation methods that only focused on vegetative phases (e.g. Cameron 1960; Cameron 1964; Ocampo-Paus & Friedmann 1966; Lange et al. 1992). More recently, Fletchtner et al. (1998) integrating morphological and life history stages in their identifcation were able to distin- guish almost 40 species collected from a small number of desert crust samples in Baja California (Mexico). Sub- sequent examinations (e.g., Lewis & Lewis 2005; Büdel et al. 2009) relied on the analysis of DNA sequence data, which has revealed a high level of biodiversity in soils of arid regions, including desert algae. Knowledge of biodi- versity of this region was further enhanced by discovery that desert-dwelling green algae belong to multiple clades in Streptophyta and Chlorophyta (Lewis & Lewis 2005). Phylogenetics-based taxonomy is key to uncov- ering novel species, enhancing knowledge of species distributions and revealing overall biodiversity from dif- ferent habitats. Phylogenetics-based taxonomy is espe- cially relevant for groups of microscopic organisms and those, that do not possess multiple charismatic morpho- logical traits. With the dramatic increase in the number of algal surveys using environmental sampling and DNA barcoding, a growing number of sequences now in public databases are taxonomically unattributed or may have incorrect attributions. We therefore, test species desig- nation of existing sequences in light of our updated tax- onomy of Tetradesmus. In Chlorophyta, desert algae are members of two classes. Trebouxiophyceae, a class known for its many lichenized and free-living terrestrial species, includes members from 12 major lineages (Fučíková et al. 2014). Chlorophyceae, on the other hand, is often considered largely aquatic, but also contains multiple lineages of terrestrial algae, including species isolated from deserts (Lewis & Lewis 2005). Thus, in Chlorophyta, desert algae are not associated with a single taxon, nor do they tend to be members of predominantly terrestrial lineages; instead desert algae are embedded in clades of aquatic species, as exemplifed by the focus genus of this study Tetradesmus (Scenedesmaceae, Sphaeropleales, Chloro- phyta). Tetradesmus includes multiple arid-adapted spe- cies, which belong to two separate clades, each containing aquatic as well as terrestrial species (Lewis & Flechtner 2004; Sciuto et al. 2015; Mikhailyuk et al. 2018; Lewis & Flechtner 2019). Here we present evidence for a new terrestrial species in the mainly freshwater planktonic family 1 Department of Ecology and Evolutionary Biology, University of Con- necticut, 75 North Eagleville Rd., Storrs, CT 06269-3043, USA * Corresponding author e-mail: elizaveta.terlova@uconn.edu ISSN 2544-7459 (print) ISSN 2657-5000 (online) Plant and Fungal Systematics 64(1): 25–32, 2019 DOI: 10.2478/pfs-2019-0004 © 2019 W. Szafer Institute of Botany Polish Academy of Sciences Article info Received: 12 Feb. 2019 Revision received: 18 Apr. 2019 Accepted: 28 Apr. 2019 Published: 30 Jul. 2019 Associate Editor Judita Koreiviene This work is licensed under the Creative Commons BY-NC-ND 4.0 License Dedicated to the late Professor Jadwiga Siemińska