The phylogenetic placement of <i>Temnogametum</i> (Zygnemataceae) and description of <i>Temnogametum iztacalense</i> sp. nov., from a tropical high mountain lake in Mexico

A new species <i>Temnogametum iztacalense</i> sp. nov. (Zygnemataceae) was described using an integrative taxonomic approach. Material was collected between 2014–2019 from purple mats at the bottom of La Luna Lake, which is a shallow, well-oxygenated, acidic and ultraoligotrophic high mountain lake exposed to high levels of ultraviolet radiation. Morphological analysis revealed that the material belonged to the Zygnemataceae and contained mature zygospores of oblate-sphaeroidal shape; smooth and yellow exospores, finely punctate and brown mesospores, and thin hyaline endospores. Transmission electron microscopy showed vacuolization, wavy thylakoids and a large number of starch granules and plastoglobules. The topology of the concatenated 18S-<i>rbc</i>L tree using the Bayesian method separated <i>T. iztacalense</i> into an independent branch within the Zygnematales. The chromatographic profile of <i>T. iztacalense</i> revealed 20 compounds, the major ones being lutein (596.9 ± 20.9 mg g^–1 algae) and β-carotene (171.4 ± 3.3 mg g^–1 algae). This is the first reported phylogeny of <i>Temnogametum</i> isolated from this kind of lake based on 18S-<i>rbc</i>L sequences.