Stichococcus Nägeli.

Veselá, Veronika, Malavasi, Veronica & Škaloud, Pavel, 2024, A synopsis of green-algal lichen symbionts with an emphasis on their free-living lifestyle, Phycologia 63 (3), pp. 317-338 : 326

Stichococcus Nägeli.

Stichococcus is a coccoid alga forming clusters of two cells, or short chains, which readily break into single cylindrical cells with a thin cell wall that may be curved and rounded at the edges ( Fig. 12 ). Chloroplasts are parietal, sometimes with a naked pyrenoid. Stichococcus reproduces by filament disintegration or cell division (Ettl & Gärtner 2013).

The genus was recognized to be polyphyletic ( Handa et al. 2003). However, representatives of this genus have recently been reassigned to several newly described monophyletic genera: Protostichococcus , Deuterostichococcus , Tritostichococcus and Tetratostichococcus ( Pröschold & Darienko 2020) . Since these genera are morphologically not recognizable from each other and from the genus Stichococcus s. str., we are treating them here together.

These algae inhabit both freshwater and terrestrial environments (Ettl & Gärtner 2013) and travel very long distances through the air, yet certain patterns can be traced in their distribution ( Hodač et al. 2016). Moreover, some of them have the potential for biodiesel ( Olivieri et al. 2011), and have been observed many times as photobionts of lichens ( Tschermak-Woess 1988; Thüs et al. 2011). Stichococcus mirabilis is, based on morphology, a likely photobiont of the lichen Staurothele ( Thüs et al. 2011) . Deuterostichococcus allas is a photobiont of the lichen genus Placopsis ( Beck et al. 2019) , while Tritostichococcus coniocybes associates with Chaenotheca, Chaenothecopsis and Coniocybe ( Pröschold & Darienko 2020) . A genetically confirmed record of S. mirabilis comes from a castle wall in Thuringia, Germany ( Hallmann et al. 2013). Its occurrence has also been confirmed in Antarctica soil ( Cavacini 2001), in a granite canyon of the Teteriv River, Ukraine (Mikhailyuk 2008) and in air samples from northern Florida ( Parrando & Davis 1972; North & Davis 1988). Tritostichococcus coniocybes occurs free-living in soil and on rocks ( Pröschold & Darienko 2020).

Figures

Figs 1–18. Lichen photobiont genera (including nonlichenized species) belonging to classes Trebouxiophyceae and Chlorophyceae. Fig. 1. Asterochloris lobophora. Fig. 10. Prasiola crispa. Fig. 2. Myrmecia incisa. Fig. 11. Pseudochlorella pringsheimii. Fig. 3. Trebouxia impressa. Fig. 12. Stichococcus sp. Fig. 4. Vulcanochloris symbiontica. Fig. 13. Auxenochlorella protothecoides. Fig. 5. Chloroidium saccharophilum. Fig. 14. Apatococcus sp. Fig. 6. Jaagichlorella luteoviridis. Fig. 15. Leptosira sp. Fig. 7. Coccomyxa sp. Fig. 16. Symbiochloris tschermakiae. Fig. 8. Elliptochloris subsphaerica. Fig. 17. Uvulifera verrucariae (Lorenz 2016). Fig. 9. Diplosphaera chodatii. Fig. 18. Bracteacoccus. sp. Scale bars: 10 μm (Figs 1-9, 11-18), 200 μm (Fig. 10).