Sporolithales Le Gall et G.W.Saunders Le Gall et al.， 2010
　　See family Sporolithaceae for detail. Tetrasporangia are singly located in calci.ed compartments and cruciately divided. A central fusion cell is absent in the carposporangial conceptacles. Thalli possess one-to two-celled short .laments bearing terminal carposporangium with oblong carposporangia (Modi.ed from Bahia et al. 2015).
　　Sporolithaceae Verheij Verheij， 1993
　　Thalli non-geniculate， mostly calci.ed， crustose to warty， lumpy or fruticose; epiphytic and partially to completely attached to substrate， or unattached and free living; structure pseudoparenchymatous， dorsiventral in crustose portions but radial in protuberant branches; construction monomerous. Cells of adjacent .laments usually joined by cell fusions or secondary pit-connections.
　　Life history with isomorphic gametophyte and tetrasporophyte generations and a heteromorphic carposporophyte generation. Vegetative reproduction by thallus fragmentation. Gametangia and carposporangia borne in uniporate conceptacles; tetrasporangia borne in the calci.ed compartments which are formed in solitary or aggregated into sori， and may have developed from the cell walls of tetrasporangial initials; cruciately divided， bisporangia unknown (Modi.ed from Womersley 1996).
　　Type genus: Sporolithon Heydrich.
　　Sporolithon Heydrich Heydrich， 1897a
　　Thalli encrusting to warty， lumpy or fruticose; attached or free living; construction monomerous， .laments curved toward thallus surface (plumose anatomy). The outermost cell wall of epithallial cells usually .attened and .ared. Cells of adjacent .laments often fused， sometimes with secondary pit-connections， but not common. Heterocysts or trichocytes lacking. Gametangia and carposporangia borne in uniporate conceptacles; tetrasporangia borne in calci.ed compartments that may be solitary or aggregated into sori， each tetrasporangia or bisporangia produced an apical plug; tetrasporangia cruciately divided， bisporangia rare (Modi.ed from Womersley 1996).
　　Type species: Sporolithon ptychoides Heydrich.
　　1. Sporolithon erythraeum (Rothpletz) Kylin Figs. 1-2
　　Sporolithon erythraeum (Rothpletz) Kylin 1956， p. 205; Dawson 1960， p. 41; Cabioch 1972， p. 217， text-.g. 29a， p1. 1X， .g. 2; Womersley and Bailey 1970， p. 308; Silva et al. 1996， p. 276; Xia et al. 2013， p. 2.
　　Lithothamnion erythraeum Rothpletz 1893， p. 5.
　　Lithothamnium erythraeum (Rothpletz) Foslie 1900a， p. 8; 1904 (in Weber-van Bosse and Foslie)， p. 38， p1s. V-VI; 1909， p. 4; Lemoine 1911， p. 67， text-.gs. 28–29， p1. 1， .g. 1; Johnson 1963， p. 178， 179， 181， 184， 192， 205， 206， p1. 28. .gures 1–10.
　　Archaeolithothamnion erythraeum (Rothpletz) Foslie 1900c， p. 8; Zhou and Zhang 1987， p. 115， p1. I， .g. 1–6.
　　Sporolithon ptychoides Heydrich 1897a， p. 67， .gs. 2–3; Denizot 1968， p. 207， .gs. 170–171.
　　Fig. 1 Sporolithon erythraeum (Rothpletz) Kylin (AST75-837) 1. Longitudinal section of partial perithallium; 2. Cells of adjacent .laments showing cell fusions; 3. Longitudinal section of partial hypothallial cells; 4. Longitudinal section of partial epithallial cells; 5. Longitudinal section of part of a frond， showing the sporangial sori; 6. Tetrasporangia.
　　Fig. 2 Sporolithon erythraeum (Rothpletz) Kylin (AST75-837)
　　1. Longitudinal section of part of a frond， showing the sporangial sori; 2. Longitudinal section of partial epithallial and perithallial cells; 3. Longitudinal section of a tetrasporangial compartment; 4. Cells of adjacent .laments showing cell fusions.
　　Type locality: Red Sea.
　　Thalli crustose， greenish yellow， slightly yellowish purple， gray-purplish red or cement color on drying; the color of living fronds often varied as to the degree of exposure to sunlight， usually dark purple or reddish brown in shaded areas. Thalli up to 12 cm in diameter or larger， with rather dense protuberances or round protruding branches， usually simple， or occasionally 1–2 times branched， protruding branches 3–8(–11) mm high， 2–8(–11) mm in diameter， mature crustose parts usually with protruding branches， surface smooth.
　　In longitudinal section of thallus， basal hypothallium composed of ca. 10 layers of rectangular cells， 13–36 μm long， 6–11 μm in diameter. Perithallial cells arranged more compactly， mostly subsquarish， 7–8 μm in diameter， or rectangular， (10–) 13–18(-20) μm high， and 5–8(–10) μm wide; adjacent .laments joined by cell fusions. Epithallium unistratose， cells 6–9 μm wide， 3–5 μm high.
　　Sporangial sori arranged in layers within thallus， (65–)75–90 μm high， 20–40 μm in diameter， sporangia tetrad， mostly cruciately divided and rarely zonately divided， (42–) 52–72 μm high， (18–)20–36 μm wide. Gametangial conceptacles not found.
　　Habitat: Growing on the rocks or corallites in the mid-low intertidal zones， often in calm areas with less wave exposures and with shades afforded by large algae or other substances.
　　Distribution in China: Hainan Province (Hainan Is