Chlorophyta on Land

Familiar examples of green algae (Chlorophyta) on land include those that participate in symbiotic associations with fungi, forming lichens (e.g., Coccomyxa, Myrmecia, Stichococcus, Trebouxia, Ahmadjian, 1958; Friedl, 1997), and taxa that grow richly on natural and man-made surfaces or on leaves of citrus and magnolia trees (e.g., Prasiola, Trentepohlia, Cephaleuros, Rindi and Guiry, 2004; Rindi et al., 2005). Besides these examples, green algae can occur in rock (endolithic), or at the surface (epidaphic), or just below the surface (endedaphic) of soil (Friedmann et al., 1967; Bell, 1993). Green algae are components of desert soil communities known as biological soil crusts or cryptogamic crusts (Evans and Johansen, 1999; Belnap and Lange, 2001). Crust communities are found on all continents on Earth, in arid and semi-arid habitats, where soil moisture is limiting and vascular plant cover is sparse (e.g., Johansen, 1993; Evans and Johansen, 1999; Green and Broady, 2001). Along with cyanobacteria, fungi, lichens, diatoms, and bryophytes, desert green algae form water-stable soil aggregates that have important ecological roles in nutrient cycling, water retention, and stabilization of soils (Evans and Johansen, 1999). The fragile nature of desert crust communities makes them highly susceptible to disturbance by trampling and fire, and has lead to numerous studies on the recovery of crusts after disturbance (Belnap and Eldridge, 2001; Nagy et al., 2005). Reviews of the ecology of crusts can be found in West (1990), Eldridge and Greene (1994), Evans and Johansen (1999), and Belnap and Lange (2001). This paper provides background information about the taxonomy of green algae from arid soil communities, and highlights recent studies that address the fine scale distribution, evolutionary relationships, diversification, and origins of Chlorophyta on land.