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A multi-gene (SSU, LSU, psbA, and COI) molecular phylogeny of the family Corallinaceae (excluding the subfamilies Lithophylloideae and Corallinoideae) showed a paraphyletic grouping of six monophyletic clades. Pneophyllum and Spongites were reassessed and recircumscribed using DNA sequence data integrated with morpho-anatomical comparisons of type material and recently collected specimens. We propose Chamberlainoideae subfam. nov., including the type genus Chamberlainium gen. nov., with C.tumidum comb. nov. as the generitype, and Pneophyllum. Chamberlainium is established to include several taxa previously ascribed to Spongites, the generitype of which currently resides in Neogoniolithoideae. Additionally we propose two new genera, Dawsoniolithon gen. nov. (Metagoniolithoideae), with D.conicum comb. nov. as the generitype and Parvicellularium gen. nov. (subfamily incertae sedis), with P.leonardi sp. nov. as the generitype. Chamberlainoideae has no diagnostic morpho-anatomical features that enable one to assign specimens to it without DNA sequence data, and it is the first subfamily to possess both Type 1 (Chamberlainium) and Type 2 (Pneophyllum) tetra/bisporangial conceptacle roof development. Two characters distinguish Chamberlainium from Spongites: tetra/biasporangial conceptacle chamber diameter (300m in Spongites) and tetra/bisporangial conceptacle roof thickness (8 cells in Spongites). Two characters also distinguish Pneophyllum from Dawsoniolithon: tetra/bisporangial conceptacle roof thickness (8 cells in Dawsoniolithon) and thallus construction (dimerous in Pneophyllum vs. monomerous in Dawsoniolithon).

A re-examination of the type material of Lithothamnion crispatum Hauck allowed to identify some tetrasporangial empty conceptacles that were overlooked during a previous revision. The macroscopic morphology and plant habit, the microscopic anatomy of the vegetative thallus and the tetrasporangial conceptacles of the type material have been compared with freshly collected Mediterranean plants. The 5-7 rosette cells surrounding each pore of the tetrasporangial conceptacle roof are larger than the normal epithallial cells and the whole structure (pore and rosette cells) lays in a depression below the conceptacle roof surface. The dioecius gametangial plants are described. The comparison of the reproductive anatomy of Lithothamnion superpositum Foslie 1899 and Lithothamnion crispatum Hauck 1878 shows that both species possess tetrasporangial conceptacle roofs that are pitted with depressions as a consequence of disintegration of uppermost cells in filaments surrounding pore canals. The correspondence of vegetative and reproductive characters demonstrates that they are conspecific, and therefore L. superpositum Foslie must be considered a younger heterotypic synonym of L. crispatum Hauck.

Lithophyllum okamurae has been widely reported in the Pacific Ocean with identification based on morpho-anatomical observations. Two infraspecific taxa, L. okamurae f. okamurae and f. angulare, described from Japan, have been recorded in the temperate region of Japan. We assessed branched Lithophyllum samples morphologically referable to L. okamurae using morpho-anatomical data and DNA sequences (psbA, rbcL and partial LSU rDNA) obtained from herbarium specimens, including type material, as well as recently field-collected material in Japan. The molecular analyses showed that these ‘L. okamurae’ samples contained two species: L. okamurae and a cryptic new species which we describe as L. neo-okamurae sp. nov. Because the holotype of L. okamurae f. angulare was conspecific with original material cited in the protologue of L. okamurae, it is a heterotypic synonym of L. okamurae f. okamurae. Lithophyllum okamurae and L. neo-okamurae were morphologically similar in having warty, lumpy and fruticose thalli and in often forming rhodoliths. Lithophyllum okamurae can be morpho-anatomically distinguished from L. neo-okamurae by the thallus with tapering or plate-like protuberances (knobby protuberances in the latter) and by having smaller tetrasporangial conceptacle chambers (167–314 μm; 248–380 μm in L. neo-okamurae). Our LSU rDNA sequence data from L. okamurae f. angulare (=L. okamurae f. okamurae) was identical to that of the type of L. margaritae, which has nomenclatural priority over L. okamurae. However, considering that psbA and rbcL sequences of L. margaritae type material could not be generated in the present study, we refrain, for the moment, from proposing the taxonomic synonymy between these two taxa until the status of L. margaritae and its synonyms from the type locality (Gulf of California) are clarified., This research was mainly supported by Japan Society for the Promotion of Science (JSPS KAKENHI Grant Number 26850123, 17K07908) to AK.

International audience; Species of the genus Lithophyllum are important carbonate producers and bioconstructors. In recent years, molecular studies focusing on this genus have unravelled several striking cases of cryptic and pseudocryptic diversity. Lithophyllum racemus is a common non-geniculate coralline alga-forming rhodoliths in the northeastern Atlantic Ocean and the Mediterranean Sea. Molecular phylogenies (psbA and coxI) reconstructed for some Mediterranean specimens morpho-anatomically assigned to L. racemus revealed two well-supported sister clades. Based on pairwise sequence divergences, we recognised these two clades as separate species, L. racemus and L. pseudoracemus sp. nov. The low number of specimens has not permitted any useful morpho-anatomical comparison between the species, and for now, only DNA sequencing permits separation. The discovery of L. pseudoracemus unravelled a new case of cryptic diversity in Mediterranean coralline algae, highlighting the substantially underestimated diversity of these seaweeds.

International audience; Lithophyllum species in the Mediterranean Sea function as algal bioconstructors, contributing to the formation of biogenic habitats such as coralligenous concretions. In such habitats, thalli of Lithophyllum, consisting of crusts or lamellae with entire or lobed margins, have been variously referred to as either one species, L. stictiforme, or two species, L. stictiforme and L. cabiochiae, in the recent literature. We investigated species diversity and phylogenetic relationships in these algae by sequencing three markers (psbA and rbcL genes, cox2,3 spacer), in conjunction with methods for algorithmic delimitation of species (ABGD and GMYC). Mediterranean subtidal Lithophyllum belong to a well‐supported lineage, hereby called the L. stictiforme complex, which also includes two species described from the Atlantic, L. lobatum and L. searlesii. Our results indicate that the L. stictiforme complex consists of at least 13 species. Among the Mediterranean species, some are widely distributed and span most of the western and central Mediterranean, whereas others appear to be restricted to specific localities. These patterns are interpreted as possibly resulting from allopatric speciation events that took place during the Messinian Salinity Crisis and subsequent glacial periods. A partial rbcL sequence from the lectotype of L. stictiforme unambiguously indicates that this name applies to the most common subtidal Lithophyllum in the central Mediterranean. We agree with recent treatments that considered L. cabiochiae and L. stictiforme conspecific. The diversity of Lithophyllum in Mediterranean coralligenous habitats has been substantially underestimated, and future work on these and other Mediterranean corallines should use identifications based on DNA sequences.

Rhodoliths are important marine carbonate producers that provide habitat for several marine organisms, and are threatened by ongoing global climate change. Meter-sized sedimentary patches rich in living rhodoliths, interspersed among corals, were discovered in the back reef of Ras Ghamila lagoon, Southern Sinai, at less than 1 m water depth. In this shallow and relatively sheltered subtropical environment, rhodoliths were found to be monospecific or oligospecific, spheroidal, 3.5 to 9.4 cm in maximum diameter, with warty/lumpy or fruticose (protuberance degree IV) growth forms, and corresponded to the unattached branches or praline type. They grew in bright light under seasonal, moderate, wind-driven water motion. The dominant rhodolith-forming species recorded were: Lithophyllum kotschyanum, Porolithon onkodes, Hydrolithon sp. and three species of Neogoniolithon: Neogoniolithon fosliei, Neogoniolithon brassica-florida, and an undescribed species noted in the text as Neogoniolithon sp. A total of 38 Alizarin-stained rhodoliths was released in the field and collected after 1 year. They showed different banding patterns (alternating long and short cells) that revealed seasonal growth, with the lowest rates occurring in winter for all species, and an additional summer growth slackening in Neogoniolithon fosliei. Lithophyllum kotschyanum presented evidence of occasional growth cessation, possibly due to temporary burial. The observed annual growth rate of rhodoliths was unrelated to their size. The mean accretion rates were 1.08 mm · year−1 in L. kotschyanum, 0.75 mm · year−1 in P. onkodes, 0.49 mm · year−1 in Hydrolithon sp., 0.85 mm mm · year−1 in N. fosliei, 0.63 mm · year−1 in N. brassica-florida and 0.57 mm · year−1 in Neogoniolithon sp. The annual mean marginal elongation rate for these taxa was respectively 8.74, 13.92, 3.59, 9.40 and 9.25 mm · year−1, with the exception of Neogoniolithon sp., for which this parameter was not recorded. Maximum marginal elongation occurred in P. onkodes pointing out its greater ability as a space competitor in comparison with the other rhodolith species. The highest accretion rate and common presence of L. kotschyanum indicate its importance as carbonate producer in tropical reef.

Recent investigations have shown the potential of red coralline algae as paleoclimatic archive. A previously unexplored subfamily of coralline algae, the Lithophylloideae, was investigated from the Gulf of Aden (Balhaf, Yemen). Seasonal changes in Mg/Ca, Li/Ca and Ba/Ca composition of Lithophyllum kotschyanum f. affine were investigated by Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). For the first time in coralline algae, the Li/Ca composition was analyzed and showed a highly significant and positive correlation with Mg/Ca and SST. Monthly algal Mg/Ca and Li/Ca variations indicate a positive correlation with sea surface temperature (SST), and sea surface salinity (SSS), although low growth rates decrease the resolution of the algal record. Albeit no or weak positive correlation between monthly algal Ba/Ca and local SST was found, fluctuations in Ba/Ca suggest the seasonal influence of nutrient-rich deep waters introduced by upwelling, and record an increase of sedimentation at the sampling site likely due to an intensified land use in the area. The Mg/Ca age model shows an average algal extension rate of 1.15 mm yr −1 , and reveals multiple intra-annual banding (previously unreported in the genus Lithophyllum ) together with carposporangia formation in late February-early March, when temperature begins to increase. The concentration of MgCO 3 in the thallus of L. kotschyanum f. affine is 20 mol% (1 SE), confirming that within the genus, the species sampled in warmer regions contain higher mol% MgCO 3 . The concentrations of LiCO 3 and BaCO 3 are 8 μmol% (0.7 SE) and 0.5 μmol% (0.03 SE), respectively. Despite the limitations from low-growth rate and species-specific vital effect, coralline algae confirm their utility in climate and oceanographic reconstruction.

In Yemen, off the northwestern coast in the Gulf of Aden, the coralline algae Hydrolithon rupestre (Foslie) Penrose 1996 and H. murakoshii Iryu and Matsuda 1996 have been observed to overgrow and kill living Porites lutea Milne-Edwards and Haime, 1860. Similarly, Hydrolithon onkodes (Heydrich) Penrose and Woelkerling 1992 and H. rupestre were observed overgrowing Stylophora pistillata (Esper, 1797). Competitive interactions between P. lutea and H. murakoshii were monitored from 2006 to 2009 at two sites and showed an average linear growth of 8.3 (+/- 1.9 SD) mm year(-1) over the coral. The small polyps of S. pistillata and P. lutea combined with putative chemical compounds produced by Hydrolithon spp. are likely to allow the coralline overgrowth. Although corallines can locally kill coral tissues, the CCA/coral interactions do not seem to affect the overall live coral cover at the study sites.

An innovative technique for the estimation of species and growth-form abundance of coralline algae, including information on their vitality, was adopted on the reef crest of Ras Nosrani and Coral Bay, South Sinai. Data of coralline abundance from visual census and collection of voucher specimens were plotted on a 3-D sketched representation of the horizontal and vertical planes of the reef crest and of its crannies. Coralline dominance at the two investigated sites was not significantly different, with values ranging from 8.55 and 10.06% on the vertical plane and from 5.3 to 7.17% on the horizontal plane. About one-third of total corallines of the South Sinai reef crest was located in crannies, where the algae are completely overlooked by routine field surveys. Pink to violet, healthy corallines with encrusting growth-form, mainly belonging to Hydrolithon onkodes and Neogoniolithon, with subordinate fruticose Lithophyllum kotschyanum dominated the reef crest at both sites. The fruticose growth form, usually associated with L. kotschyanum, was more common in the horizontal than in the vertical plane. Purple, healthy, encrusting Sporolithon uncommonly occurred. Whitish, gray or green unhealthy or dead corallines were more common on the horizontal plane at both sites, possibly resulting from excessive solar radiation.

Based on literature, the genus Lithophyllum was represented in the whole Indian Ocean by 14 taxa, mostly in need of revision in a modern context. Molecular analyses integrated with morpho-anatomical comparisons between the recently revised type material of Lithophyllum kotschyanum Unger, and the related infraspecific taxa, lead to a resumption of L. affine , L. kaiseri , and L. subreduncum, and the description of L. socotraense sp. nov. , L. yemenense sp. nov. , and L. subplicatum comb. et stat. nov. Detailed accounts are provided for each species, including keys, along with information on synonymy, examined collections, distribution, habitat as well as sequence data of the 5’ end of the LSU from the type specimens. The anatomical features of the tetrasporangial conceptacle that were considered collectively diagnostic for species identification are: the mean diameter of the tetrasporangial conceptacles, the length of the pore-canal in the tetrasporangial conceptacles (with the number of cells in roof filaments), the occurrence of a depression at the top of the conceptacle roof in relation to the pore opening, and the number of cells from the floor of the tetrasporangial conceptacle chamber to the thallus surface. This study provides evidence of a previously unsuspected diversity within the Red Sea and NW Indian Ocean species of Lithophyllum.

Tetrasporangial male and female/carposporangial plants of a Mediterranean population of Spongites fruticulosus are described and compared with the type material of S. fruticulosus, Spongites racemosa and Spongites stalactitica. The three species were established by Kutzing on the basis of Mediterranean collections. The type material of S. fruticulosus is a rhodolith composed of a tetrasporangial plant possessing uniporate conceptacles, multistratose noncoaxial hypothallium and ovoid epithallial cells, growing on another unidentified sterile coralline with different vegetative characters. Spongites fruticulosus is lectotypified here with the tetrasporangial plant. The original material of S. racemosa represents a male plant of Neogoniolithon, here identified as Neogoniolithon racemosum (Kutzing) comb. nov. The type material of S. stalactitica is a rhodolith composed of a mixture of two species belonging to different genera: one, here selected as lectotype of S. stalactitica, is a female plant regarded as conspecific with S. fruticulosus. The second is the tetrasporophyte of a Neogoniolithon species. Detailed morphological-anatomical accounts of the species are presented, and their features are documented and discussed. The comparison between the Mediterranean types and new collections and the Australian population of S. fruticulosus revealed that Mediterranean plants have smaller sexual and asexual conceptacles and lack trichocytes. However, overlap in conceptacle dimensions and the rarity of trichocytes in the Australian specimens do not allow us to separate the Mediterranean and the Indo-Pacific populations into different species at this time.

The current diagnosis of the genus Lithophyllum includes absent or rare trichocyte occurrence. After examining holotype material, single trichocytes have been revealed to occur abundantly in Lithophyllum kotschyanum Unger, and in freshly collected specimens of Lithophyllum spp. from the Red Sea, Gulf of Aden and Socotra Island (Yemen). Trichocyte occurrence is not considered a diagnostic character at specific or supraspecific levels in the Lithophylloideae, and the ecological significance of trichocyte formation is discussed. The generitype species, L. incrustans Philippi, does not show trichocytes nor do many other Lithophyllum species from diverse geographic localities, but the presence of abundant trichocytes in other congeneric taxa requires emendation of the genus diagnosis. Therefore, the diagnosis of Lithophyllum is here emended by eliminating the adjective "rare" in the sentence concerning trichocyte occurrence, as follows: "Trichocytes present or absent, if present occurring singly."

After re-examination of the original Hauck's collection, a buried, empty multiporate tetrasporangial conceptacle was detected in the lectotype material of Lithothamnion crispatum. The morphology and anatomy of the type material were compared to freshly collected representative plants from the Mediterranean. In L. crispatum, the five to seven rosette cells surrounding each pore of the tetra/bisporangial conceptacle roof are larger than the normal epithallial cells and undergo degeneration. As a consequence of the disintegration of the outermost cells in filaments surrounding the pore canals, the tetra/bisporangial conceptacle roofs appear pitted with depressions, each one hosting a pore and the surrounding rosette cells. A previous revision of the type material of Lithothamnion superpositum from South Africa showed this same tetra/bisporangial conceptacle roof structure and development, and corresponding vegetative and reproductive characters. These taxa are thus conspecific; therefore, L. superpositum is a younger heterotypic synonym of L. crispatum, the latter having nomenclatural priority. While the type specimen lacked gametangial plants, these are described for representative freshly collected material and found to be dioecious.

Lithothamnion minervae is a crustose coralline alga recognized as a common rhodolith-forming species in the western Mediterranean basin. The species was erected in order to give a correct name and an unequivocal definition to the coralline misidentified for a long time as Lithothamnion fruticulosum. Details of the plant, such as the epithallial cells and the tetrasporangial or bisporangial and uniporate conceptacles are described on recently collected samples. It is shown that the two plants in the original collection of Millepora fasciculata belong to different taxa, and therefore a previous lectotypification (Woelkerling in Woelkerling & Lamy 1998) is superseded. The smaller of the two plants, which belongs to an undescribed species of Clathromorphum, is selected here as the new lectotype of M. fasciculata. The larger plant in the collection belongs to a species of Lithothamnion; it differs from L. minervae in having a smaller range of chamber diameters of multiporate conceptacles. embedded multiporate conceptacles filled with palisade cells and smaller perithallial cells.