Leptosira A. Borzì.

The thallus of the photobiont genus Leptosira is composed of cushion-shaped clusters of filaments with short lateral branches (Fig. 15). A parietal chloroplast with or without a pyrenoid (Bakker et al. 1997) is located inside spherical cells with a single nucleus. Leptosira reproduces asexually by zoospores and aplanospores. However, in the lichenized state, the appearance of the thallus changes dramatically – as a photobiont it forms ellipsoidal or spherical single cells (Tschermak-Woess 1988).

This genus closely resembles the genus Pleurastrum (Guiry & Guiry 2022). In the past, several species of Pleurastrum were reassigned to Leptosira based on examination of morphology and later molecular data (Friedl 1996). Li et al. (2021) places this genus close to Xylochloris and Dictyochloropsis. However, this placement remains uncertain (Sanders & Masumoto 2021).

The genus currently includes seven taxonomically accepted species (Guiry & Guiry 2022), two of which, L. obovata and L. thrombii, enter lichen symbiotic associations (Tschermak-Woess 1988; Roldán et al. 2004). A record of L. obovata comes from a cavity in limestone in the Garraf Mountains (Spain), where the species occurred both free-living and as a photobiont of the lichen Macentina stigonemoides (Roldán et al. 2004).