The lichenized green microalga Trebouxia lynnae Barreno has been recently described and
is considered a model organism for studying lichen chlorobionts. Its cellular ultrastructure has already
been studied in detail by light, electron, and confocal microscopy, and its nuclear, chloroplast
and mitochondrial genomes have been sequenced and annotated. Here, we investigated in detail
the ultrastructure of in vitro grown cultures of T. lynnae observed by Low Temperature Scanning
Electron Microscopy (LTSEM) applying a protocol with minimum intervention over the biological
samples. This methodology allowed for the discovery of ultrastructural features previously unseen
in Trebouxiophyceae microalgae. In addition, original Transmission Electron Microscopy (TEM) images
of T. lynnae were reinterpreted based on the new information provided by LTSEM. The nucleolar
vacuole, dictyosomes, and endoplasmic reticulum were investigated and reported for the first
time in T. lynnae and most likely in other Trebouxia lineages.
