Phylogenetic relationships of corallinaceae (Corallinales, Rhodophyta): taxonomic implications for reef-building corallines

A multiscale analysis of coralline algae Lithophylloideae (Corallinophycidae, Rhodophyta) shedding new light on understanding cryptic diversity

Cryptic diversity abounds in many biological species, posing challenges to our understanding of biological diversity, conservation and management. Taking the common coralline algae, the subfamily Lithophylloideae as an illustration, this study delved into the implications of cryptic diversity through global-level phylogenetic and geographical analysis based upon Lithophylloideae molecular data worldwide, as well as a multi-locus time-calibrated phylogeny to elucidate their possible evolutionary process. The multiscale analysis revealed the polyphyly in current concept of the genus Lithophyllum. Geographic isolation resulting from the Tethys terminal event (TTE) has led to two distinct distribution regions for this so-called cosmopolitan genus: one regionally distributed along European coasts/Mediterranean that should include the taxonomical Lithophyllum; others widely distributed, particularly among pan-tropic waters, suggesting at least five groups to be rediscovered within the subfamily Lithophylloideae. Meanwhile, the cryptic genus Titanoderma, lacking morphological identification features with Lithophyllum, exhibited differences in distribution and evolutionary patterns consistent with their ecological habits, thus supporting their separation. This study provided useful hints for cryptic diversity, which advocated an integrative thinking to investigating global cryptic diversity and exploring the broad linkages between phylogenetic relationships and evolutionary origin, biogeography, morphological and ecological traits to achieve a more comprehensive understanding of biodiversity.

"Pink power"-the importance of coralline algal beds in the oceanic carbon cycle

Current evidence suggests that macroalgal-dominated habitats are important contributors to the oceanic carbon cycle, though the role of those formed by calcifiers remains controversial. Globally distributed coralline algal beds, built by pink coloured rhodoliths and maerl, cover extensive coastal shelf areas of the planet, but scarce information on their productivity, net carbon flux dynamics and carbonate deposits hampers assessing their contribution to the overall oceanic carbon cycle. Here, our data, covering large bathymetrical (2-51 m) and geographical ranges (53°N-27°S), show that coralline algal beds are highly productive habitats that can express substantial carbon uptake rates (28-1347 g C m-2 day-1), which vary in function of light availability and species composition and exceed reported estimates for other major macroalgal habitats. This high productivity, together with their substantial carbonate deposits (0.4-38 kilotons), renders coralline algal beds as highly relevant contributors to the present and future oceanic carbon cycle.

Marine Flora of French Polynesia: An Updated List Using DNA Barcoding and Traditional Approaches

Located in the heart of the South Pacific Ocean, the French Polynesian islands represent a remarkable setting for biological colonization and diversification, because of their isolation. Our knowledge of this region's biodiversity is nevertheless still incomplete for many groups of organisms. In the late 1990s and 2000s, a series of publications provided the first checklists of French Polynesian marine algae, including the Chlorophyta, Rhodophyta, Ochrophyta, and Cyanobacteria, established mostly on traditional morphology-based taxonomy. We initiated a project to systematically DNA barcode the marine flora of French Polynesia. Based on a large collection of ~2452 specimens, made between 2014 and 2023, across the five French Polynesian archipelagos, we re-assessed the marine floral species diversity (Alismatales, Cyanobacteria, Rhodophyta, Ochrophyta, Chlorophyta) using DNA barcoding in concert with morphology-based classification. We provide here a major revision of French Polynesian marine flora, with an updated listing of 702 species including 119 Chlorophyta, 169 Cyanobacteria, 92 Ochrophyta, 320 Rhodophyta, and 2 seagrass species-nearly a two-fold increase from previous estimates. This study significantly improves our knowledge of French Polynesian marine diversity and provides a valuable DNA barcode reference library for identification purposes and future taxonomic and conservation studies. A significant part of the diversity uncovered from French Polynesia corresponds to unidentified lineages, which will require careful future taxonomic investigation.

Taxonomic contributions to Hapalidiales (Corallinophycidae, Rhodophyta): Boreolithothamnion gen. nov., Lithothamnion redefined and with three new species and Roseolithon with new combinations

Phylogenetic analyses of rbcL gene sequences and of concatenated rbcL, psbA, and nuclear SSU rRNA gene sequences resolved the generitype of Lithothamnion, L. muelleri, in a clade with three other southern Australian species, L. kraftii sp. nov., L. saundersii sp. nov., and L. woelkerlingii sp. nov. Cold water boreal species currently classified in Lithothamnion and whose type specimens have been sequenced are transferred to Boreolithothamnion gen. nov., with B. glaciale comb. nov. as the generitype. The other species are B. giganteum comb. nov., B. phymatodeum comb. nov., and B. sonderi comb. nov., whose type specimens are newly sequenced, and B. lemoineae comb. nov., B. soriferum comb. nov., and B. tophiforme comb. nov., whose type specimens were already sequenced. Based on rbcL sequences from the type specimens of Lithothamnion crispatum, L. indicum, and L. superpositum, each is recognized as a distinct species and transferred to the recently described Roseolithon as R. crispatum comb. nov., R. indicum comb. nov., and R. superpositum com. nov., respectively. To correctly assign species to these three genera based only on morpho-anatomy, specimens must have multiporate conceptacles and some epithallial cells with flared walls. The discussion provides examples demonstrating that only with phylogenetic analyses of DNA sequences can the evolution of morpho-anatomical characters of non-geniculate corallines be understood and applied at the correct taxonomic rank. Finally, phylogenetic analyses of DNA sequences support recognition of the Hapalidiales as a distinct order characterized by having multiporate tetra/bisporangial conceptacles, and not as a suborder of Corallinales whose tetra/bisporangial conceptacles are uniporate.

Phymatolithopsis gen. nov. (Hapalidiales, Corallinophycidae, Rhodophyta) based on molecular and morpho-anatomical evidence

A multigene (psbA, rbcL, 18S rDNA) molecular phylogeny of the genus Phymatolithon showed a polyphyletic grouping of two monophyletic clades within the Hapalidiales. DNA sequence data integrated with morpho-anatomical comparisons of type material and of recently collected specimens were used to establish Phymatolithopsis gen. nov. with three species, P. prolixa comb. nov., the generitype, P. repanda comb. nov. and P. donghaensis sp. nov. Phymatolithopsis is sister to Mesophyllum and occurs in a clade distinct from Phymatolithon and boreal species currently assigned to Lithothamnion. Morpho-anatomically, Phymatolithopsis is comprised of species that are non-geniculate and encrusting, bear epithallial cells with rounded walls (not flared), subepithallial initials that are usually as short as or shorter than their immediate inward derivatives, conceptacle primordia from all stages forming superficially directly from subepithallial initials, mature carposporangial conceptacles with a discontinuous fusion cell, gonimoblast filaments that develop at the margins of the fusion cell around the periphery of the carposporangial conceptacle chambers, and multiporate tetra/bisporangial conceptacles. Phymatolithopsis can be distinguished from Phymatolithon by the origin of its conceptacle primordia, which are initiated superficially, directly from the layer of subepithallial initials below the epithallial cells and the distribution of gonimoblast filaments in carposporangial conceptacles, that are at the margins of the fusion cells.

Deep Learning Applied to SEM Images for Supporting Marine Coralline Algae Classification

The classification of coralline algae commonly relies on the morphology of cells and reproductive structures, along with thallus organization, observed through Scanning Electron Microscopy (SEM). Nevertheless, species identification based on morphology often leads to uncertainty, due to their general plasticity. Evolutionary and environmental studies featured coralline algae for their ecological significance in both recent and past Oceans and need to rely on robust taxonomy. Research efforts towards new putative diagnostic tools have recently been focused on cell wall ultrastructure. In this work, we explored a new classification tool for coralline algae, using fine-tuning pretrained Convolutional Neural Networks (CNNs) on SEM images paired to morphological categories, including cell wall ultrastructure. We considered four common Mediterranean species, classified at genus and at the species level (Lithothamnion corallioides, Mesophyllum philippii, Lithophyllum racemus, Lithophyllum pseudoracemus). Our model produced promising results in terms of image classification accuracy given the constraint of a limited dataset and was tested for the identification of two ambiguous samples referred to as L. cf. racemus. Overall, explanatory image analyses suggest a high diagnostic value of calcification patterns, which significantly contributed to class predictions. Thus, CNNs proved to be a valid support to the morphological approach to taxonomy in coralline algae.

Major loss of coralline algal diversity in response to ocean acidification

Calcified coralline algae are ecologically important in rocky habitats in the marine photic zone worldwide and there is growing concern that ocean acidification will severely impact them. Laboratory studies of these algae in simulated ocean acidification conditions have revealed wide variability in growth, photosynthesis and calcification responses, making it difficult to assess their future biodiversity, abundance and contribution to ecosystem function. Here, we apply molecular systematic tools to assess the impact of natural gradients in seawater carbonate chemistry on the biodiversity of coralline algae in the Mediterranean and the NW Pacific, link this to their evolutionary history and evaluate their potential future biodiversity and abundance. We found a decrease in the taxonomic diversity of coralline algae with increasing acidification with more than half of the species lost in high pCO₂ conditions. Sporolithales is the oldest order (Lower Cretaceous) and diversified when ocean chemistry favoured low Mg calcite deposition; it is less diverse today and was the most sensitive to ocean acidification. Corallinales were also reduced in cover and diversity but several species survived at high pCO₂ ; it is the most recent order of coralline algae and originated when ocean chemistry favoured aragonite and high Mg calcite deposition. The sharp decline in cover and thickness of coralline algal carbonate deposits at high pCO₂ highlighted their lower fitness in response to ocean acidification. Reductions in CO₂ emissions are needed to limit the risk of losing coralline algal diversity.

DNA sequencing of type material and newly collected specimens reveals two heterotypic synonyms for Harveylithon munitum (Metagoniolithoideae, Corallinales, Rhodophyta) and three new species

Nongeniculate coralline algae are difficult to identify based solely on morpho-anatomy. To address the systematics of several taxonomically challenging taxa, we analyzed DNA sequences of a short portion (118-296 base pairs) of the 3' end of the rbcL gene from three type specimens. The analyses revealed that Harveylithon munitum (basionym: Lithophyllum munitum), described in 1906 from Cave Cays, Exuma Chain, Bahamas, is conspecific with both Goniolithon accretum and Goniolithon affine, described in 1906 from Sand Key, Florida and in 1907 from Culebra Island, Puerto Rico, respectively. Lithophyllum munitum and G. accretum were described in the same 1906 publication and have equal priority. We have selected the currently accepted and most commonly used name H. munitum to apply to this entity. Comparative analyses of rbcL, psbA, UPA, COI, and LSU sequences from contemporary field-collected specimens revealed that H. munitum currently inhabits mesophotic rhodolith beds in the northwestern Gulf of Mexico, as well as the intertidal zone in the Florida Keys, Honduras, Atlantic Mexico, Caribbean Panama, and Guadeloupe, French West Indies. Species delimitation analyses reveal that the Western Atlantic and Australian H. munitum populations may be separate species. Two new species of Harveylithon from the northwestern Gulf of Mexico and one new species from the southwestern Gulf of Mexico, the Caribbean, and the Red Sea were also identified in the analyses and are described.

Corallinapetrales and Corallinapetraceae: A new order and family of coralline red algae including Corallinapetra gabrielii comb. nov

The coralline algal genus Corallinapetra is currently monospecific and was established on the species Corallinapetra novaezelandiae, known from a single collection from north-eastern New Zealand. On the basis of multi-gene phylogenetic analyses, Corallinapetra has been resolved apart from all currently recognized families and orders within the Corallinophycidae. We analyzed DNA sequence data from the holotype of Lithothamnion gabrielii, which has been considered a heterotypic synonym of L. muelleri, and an unidentified sample collected from Stewart Island in New Zealand, using psbA, rbcL, and COI-5P genes. We also observed detailed morpho-anatomical characters with light and scanning electron microscopy. Our phylogenetic analyses showed that L. gabrielii and the sample from New Zealand belonged to the same clade as Corallinapetra, distinct from other families and orders in the Corallinophycidae. Members of this clade are distinguishable from other families and orders in the Corallinophycidae by possessing sporangia that are surrounded by remnant sterile filaments that are weakly calcified in mature multiporate sporangial conceptacles that produce zonately divided tetrasporangia. Therefore, we propose that Corallinapetra be placed in its own family, Corallinapetraceae and order, Corallinapetrales, and that L. gabrielii should be assigned to Corallinapetra, as C. gabrielii, to reflect their phylogenetic relationships. We also obtained a partial rbcL sequence data from the lectotype of L. muelleri, the generitype of Lithothamnion. Comparison of the L. muelleri type sequence with L. gabrielii unambiguously demonstrated that these two species are not conspecific, and confirm the placement of L. muelleri within the Hapalidiales.

A possible link between coral reef success, crustose coralline algae and the evolution of herbivory

Crustose coralline red algae (CCA) play a key role in the consolidation of many modern tropical coral reefs. It is unclear, however, if their function as reef consolidators was equally pronounced in the geological past. Using a comprehensive database on ancient reefs, we show a strong correlation between the presence of CCA and the formation of true coral reefs throughout the last 150 Ma. We investigated if repeated breakdowns in the potential capacity of CCA to spur reef development were associated with sea level, ocean temperature, CO₂ concentration, CCA species diversity, and/or the evolution of major herbivore groups. Model results show that the correlation between the occurrence of CCA and the development of true coral reefs increased with CCA diversity and cooler ocean temperatures while the diversification of herbivores had a transient negative effect. The evolution of novel herbivore groups compromised the interaction between CCA and true reef growth at least three times in the investigated time interval. These crises have been overcome by morphological adaptations of CCA.

Sporolithon franciscanum sp. nov. (Sporolithales, Rhodophyta), a New Rhodolith-Forming Species from Northeast Brazil

This paper describes Sporolithon franciscanum, a new rhodolith-forming species of non-geniculate coralline algae found at depths between 47–52 m near the São Francisco river mouth, the second largest and the most extensive drainage basin in Brazil, and also at the Abrolhos Bank, in the world´s largest rhodolith beds. DNA sequences from plastidial psbA and rbcL markers indicate that the species is unique compared to all other Sporolithon species that have thus far been sequenced. Since morpho-anatomical features of the new species are shared with some other Sporolithon species, its identification was only confirmed by DNA sequences.

Nanocrystals as phenotypic expression of genotypes-An example in coralline red algae

Coralline red algae (CRA) are important ecosystem engineers in the world's oceans. They play key roles as primary food source and carbonate producers in marine habitats. CRA are also vital for modern reef systems where they act as substrate for coral growth and stabilizers of reef frameworks. However, morphotaxonomic identification of these important marine organisms is hampered by the fact that morphological concepts used for their classification do not correspond to molecular data. We present the first analysis of nanoscale features in calcified cell walls of CRA in a globally distributed sample set. We use new morphological traits based on these cell wall ultrastructures to construct an independent morphological phyletic tree that shows a promising congruency with existing CRA molecular phylogenies. Our results highlight cellular ultrastructures as a tool to define the phenotypic expression of genotypic information showing their potential to unify morphology with molecular phylogeny.

High diversity of coralline algae in New Zealand revealed: Knowledge gaps and implications for future research

Coralline algae (Corallinophycideae) are calcifying red algae that are foundation species in euphotic marine habitats globally. In recent years, corallines have received increasing attention due to their vulnerability to global climate change, in particular ocean acidification and warming, and because of the range of ecological functions that coralline algae provide, including provisioning habitat, influencing settlement of invertebrate and other algal species, and stabilising reef structures. Many of the ecological roles corallines perform, as well as their responses to stressors, have been demonstrated to be species-specific. In order to understand the roles and responses of coralline algae, it is essential to be able to reliably distinguish individual species, which are frequently morphologically cryptic. The aim of this study was to document the diversity and distribution of coralline algae in the New Zealand region using DNA based phylogenetic methods, and examine this diversity in a broader global context, discussing the implications and direction for future coralline algal research. Using three independent species delimitation methods, a total of 122 species of coralline algae were identified across the New Zealand region with high diversity found both regionally and also when sampling at small local spatial scales. While high diversity identified using molecular methods mirrors recent global discoveries, what distinguishes the results reported here is the large number of taxa (115) that do not resolve with type material from any genus and/or species. The ability to consistently and accurately distinguish species, and the application of authoritative names, are essential to ensure reproducible science in all areas of research into ecologically important yet vulnerable coralline algae taxa.

Reef-building coralline algae from the Southwest Atlantic: filling gaps with the recognition of Harveylithon (Corallinaceae, Rhodophyta) on the Brazilian coast

The Southwest Atlantic is notable for having extensive reef areas cemented by nongeniculate coralline red algae. Based on an analysis of four genetic markers and morpho-anatomical features, we clarify the species of Harveylithon in the tropical and warm temperate Southwest Atlantic. Species delimitation methods (mBGD, ABGD, SPN, and PTP), using three markers (psbA, rbcL, and COI), support the recognition of three new species: H. catarinense sp. nov., H. maris-bahiensis sp. nov., and H. riosmenum sp. nov., previously incorrectly called Hydrolithon samoënse. Our findings highlight the importance of using an approach with several lines of evidence to solve the taxonomic status of the cryptic species.

Mediterranean Lithophyllum stictiforme (Corallinales, Rhodophyta) is a genetically diverse species complex: implications for species circumscription, biogeography and conservation of coralligenous habitats

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.

Adeylithon bosencei gen. et sp. nov. (Corallinales, Rhodophyta): a new reef-building genus with anatomical affinities with the fossil Aethesolithon

Adeylithon gen. nov. with one species, A. bosencei sp. nov., belonging to the subfamily Hydrolithoideae is described from Pacific coral reefs based on psbA sequences and morpho-anatomy. In contrast with Hydrolithon, A. bosencei showed layers of large polygonal "cells," which resulted from extensive lateral fusions of perithallial cells, interspersed among layers of vegetative cells. This anatomical feature is shared with the fossil Aethesolithon, but lacking DNA sequences from the fossils and the fragmentary nature of Aethesolithon type material, we cannot ascertain if Adeylithon and Aethesolithon are congeneric. Morpho-anatomical features of A. bosencei were generally congruent with diagnostic features of the subfamily Hydrolithoideae: (i) outline of cell filaments entirely lost in large portions due to pervasive and extensive cell fusions, (ii) trichocytes not arranged in tightly packed horizontal fields, (iii) basal layer without palisade cells, and (iv) cells lining the canal pore oriented more or less perpendicular to roof surface and not protruding into the canal. However, it showed a predominant monomerous thallus organization and trichocytes were disposed in large pustulate, horizontal fields, although they were not tightly packed and did not become distinctly buried in the thallus. Only mature tetrasporangial conceptacles were observed, therefore the type of conceptacle roof formation remained undetermined. Adeylithon bosencei occurs on shallow coral reefs, in Australia, Papua New Guinea, and South Pacific islands (Fiji, Vanuatu). Fossil Aethesolithon is considered an important component of shallow coral reefs since the Miocene; fossil records showed a broad Indo-Pacific distribution, but a long-term process of range contraction in the last 2.6 million years, resulting in an overlap with the distribution of the extant Adeylithon. While the congeneric nature of extant and fossil taxa remained uncertain, similarities in morpho-anatomy, habitat, and distribution may indicate that both taxa likely shared a common ancestor.

Evolutionary reversals in Bossiella (Corallinales, Rhodophyta): first report of a coralline genus with both geniculate and nongeniculate species

This is the first report of a coralline genus with both geniculate (upright fronds with non-calcified joints) and nongeniculate species that has been verified by DNA sequence data. Two nongeniculate (crustose) species of Bossiella are recognized, B. mayae sp. nov. and B. exarticulata sp. nov. DNA sequencing of the lectotype specimen of Pseudolithophyllum whidbeyense revealed that this name had been misapplied and instead belongs to an undescribed coralline species in the Hapalidiales. Phylogenetic analyses of concatenated DNA sequences (psbA, rbcL, COI-5P) indicate that B. mayae and B. exarticulata represent phenotypic reversals from the geniculate character state back to the nongeniculate character state. Secondary loss of genicula has occurred three times in the subfamily Corallinoideae, once to generate the entirely nongeniculate genus Crusticorallina and twice in the now morphologically heterotypic Bossiella. Since phenotypic reversals have occurred several times during the evolution of coralline algae, we speculate about the putative mechanism and adaptive significance of this phenomenon.

Revision of Corallinaceae (Corallinales, Rhodophyta): recognizing Dawsoniolithon gen. nov., Parvicellularium gen. nov. and Chamberlainoideae subfam. nov. containing Chamberlainium gen. nov. and Pneophyllum

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 (<300 μm in Chamberlainium vs. >300 μm in Spongites) and tetra/bisporangial conceptacle roof thickness (<8 cells in Chamberlainium vs. >8 cells in Spongites). Two characters also distinguish Pneophyllum from Dawsoniolithon: tetra/bisporangial conceptacle roof thickness (<8 cells in Pneophyllum vs. >8 cells in Dawsoniolithon) and thallus construction (dimerous in Pneophyllum vs. monomerous in Dawsoniolithon).

Reduced spore germination explains sensitivity of reef-building algae to climate change stressors

Reduced seawater pH and changes in carbonate chemistry associated with ocean acidification (OA) decrease the recruitment of crustose coralline algae (CCAcf.), an important coral-reef builder. However, it is unclear whether the observed decline in recruitment is driven by impairment of spore germination, or post-settlement processes (e.g. space competition). To address this, we conducted an experiment using a dominant CCA, Porolithon cf. onkodes to test the independent and combined effects of OA, warming, and irradiance on its germination success and early development. Elevated CO2 negatively affected several processes of spore germination, including formation of the germination disc, initial growth, and germling survival. The magnitude of these effects varied depending on the levels of temperature and irradiance. For example, the combination of high CO2 and high temperature reduced formation of the germination disc, but this effect was independent of irradiance levels, while spore abnormalities increased under high CO2 and high temperature particularly in combination with low irradiance intensity. This study demonstrates that spore germination of CCA is impacted by the independent and interactive effects of OA, increasing seawater temperature and irradiance intensity. For the first time, this provides a mechanism for how the sensitivity of critical early life history processes to global change may drive declines of adult populations of key marine calcifiers.

The coralline genera Sporolithon and Heydrichia (Sporolithales, Rhodophyta) clarified by sequencing type material of their generitypes and other species

Interspecific systematics in the red algal order Sporolithales remains problematic. To re-evaluate its species, DNA analyses were performed on historical type material and recently collected specimens assigned to the two genera Sporolithon and Heydrichia. Partial rbcL sequences from the lectotype specimens of Sporolithon ptychoides (the generitype species) and Sporolithon molle, both from El Tor, Egypt, are exact matches to field-collected topotype specimens. Sporolithon crassum and Sporolithon erythraeum also have the same type locality; material of the former appears to no longer exist, and we were unable to PCR amplify DNA from the latter. A new species, Sporolithon eltorensis, is described from the same type locality. We have not found any morpho-anatomical characters that distinguish these three species. No sequenced specimens reported as S. ptychoides from other parts of the world represent this species, and likely reports of S. ptychoides and S. molle based on morpho-anatomy are incorrect. A partial rbcL sequence from the holotype of Sporolithon dimotum indicates it is not a synonym of S. ptychoides, and data from the holotype of S. episporum confirm its specific recognition. DNA sequences from topotype material of Heydrichia woelkerlingii, the generitype species, and isotype material of Heydrichia cerasina confirm that these are distinct species; the taxon reported to be H. woelkerlingii from New Zealand is likely an undescribed species. Type specimens of all other Sporolithon and Heydrichia species need to be sequenced to confirm that they are distinct species; morpho-anatomical studies have proved inadequate for this task.

Timing of the evolutionary history of Corallinaceae (Corallinales, Rhodophyta)

The temporal dimension of the most recent Corallinaceae (order Corallinales) phylogeny was presented here, based on first occurrence time estimates from the fossil record. Calibration of the molecular clock of the genetic marker SSU entailed a separation of Corallinales from Hapalidiales in the Albian (Early Cretaceous ~105 mya). Neither the calibration nor the fossil record resolved the succession of appearance of the first three emerging subfamilies: Mastophoroideae, Corallinoideae, and Neogoniolithoideae. The development of the tetra/bisporangial conceptacle roofs by filaments surrounding and interspersed among the sporangial initials was an evolutionary novelty emerging at the Cretaceous-Paleogene boundary (~66 mya). This novelty was shared by the subfamilies Hydrolithoideae, Metagoniolithoideae, and Lithophylloideae, which diverged in the early Paleogene. Subclades within the Metagoniolithoideae and Lithophylloideae diversified in the late Oligocene-middle Miocene (~28-12 mya). The most common reef corallinaceans (Hydrolithon, Porolithon, Harveylithon, "Pneophyllum" conicum, and subclades within Lithophylloideae) appeared in this interval in the Indo-Australian Archipelago.

Crusticorallina gen. nov., a nongeniculate genus in the subfamily Corallinoideae (Corallinales, Rhodophyta)

Molecular phylogenetic analyses of 18S rDNA (SSU) gene sequences confirm the placement of Crusticorallina gen. nov. in Corallinoideae, the first nongeniculate genus in an otherwise geniculate subfamily. Crusticorallina is distinguished from all other coralline genera by the following suite of morpho-anatomical characters: (i) sunken, uniporate gametangial and bi/tetrasporangial conceptacles, (ii) cells linked by cell fusions, not secondary pit connections, (iii) an epithallus of 1 or 2 cell layers, (iv) a hypothallus that occupies 50% or more of the total thallus thickness, (v) elongate meristematic cells, and (vi) trichocytes absent. Four species are recognized based on rbcL, psbA and COI-5P sequences, C. painei sp. nov., the generitype, C. adhaerens sp. nov., C. nootkana sp. nov. and C. muricata comb. nov., previously known as Pseudolithophyllum muricatum. Type material of Lithophyllum muricatum, basionym of C. muricata, in TRH comprises at least two taxa, and therefore we accept the previously designated lectotype specimen in UC that we sequenced to confirm its identity. Crusticorallina species are very difficult to distinguish using morpho-anatomical and/or habitat characters, although at specific sites, some species may be distinguished by a combination of morpho-anatomy, habitat and biogeography. The Northeast Pacific now boasts six coralline endemic genera, far more than any other region of the world.