Carposporangial Conceptacles Research Articles

Reproductive phenology of a dominant crustose coralline alga, Sporolithon sp., from Taoyuan algal reefs in Northwest Taiwan

ABSTRACTSporolithon is a common genus of crustose coralline algae occurring at Taoyuan algal reefs in Northwest Taiwan. However, little is known of the reproductive cycles and growth pattern of the genus in relation to environmental changes. In this study, the asexual and sexual reproductive stages of a dominant species of Sporolithon (Sporolithon sp.) occurring in different seasons were documented in detail for the first time based on collections made from the reefs during 2020–2022. Sexual reproductive structures (spermatangial or carposporangial conceptacles) were found all year round, whereas asexual reproductive structures (tetrasporangial compartments) appeared only in the summer and autumn, when sea surface temperature rose above 25°C. These results suggest that the reproductive cycle of this dominant species of Sporolithon is largely affected by sea surface temperature, which ranged between 13.5 and 31.5°C. Furthermore, the high ratio of sterile thalli found in most seasons suggests that the dominant Sporolithon sp. can thrive in environments having variable temperature by vegetative growth. In addition, almost all old gametophytes of Sporolithon sp. have multiple bands of embedded spermatangial or carposporangial conceptacles (up to six layers), suggesting that Sporolithon sp. is a perennial species. Further investigation into the growth pattern and reproductive cycles for other reef-building crustose coralline species occurring in Taoyuan algal reefs is needed to establish a set of biological baseline data for future conservation plans and guidelines.

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.

Phragmope discrepans, gen. & comb. nov. (Mesophyllaceae, Corallinales, Rhodophyta), the species known as ‘Mesophyllum engelhartii’ from South Africa

ABSTRACT Phragmope discrepans (Lithothamnion discrepans) is recognized as a new monotypic genus endemic to South Africa on account of several active modes of growth, including apical meristem replacement, production of cell bars in canals of multiporate conceptacles, and development of a second compact, imperforate roof over multiporate conceptacles. Meristem replacement involves up to three layers. Development of cell bars starts with production of projecting cells from basal cells of lining filaments, and these cells subsequently coalesce to form a barrier. Subepithallial divisions produce a second compact roof that is composed of 1–2 perithallial cells and a layer of epithallial cells. It is assumed that these novelties reflect evolutionary advancements to overcome competition and the environmental pressure that Phragmope experiences in the intertidal zone. The new genus is taxonomically distant to the Northern Hemisphere genus Mesophyllum, and relates closer to taxa from the Southern Hemisphere, including Melyvonnea that occurs in South Africa and species of Mesophyllum sensu lato from Chatham-New Zealand-Australia, which collectively display a reduced fusion cell and lack of a pedestal in carposporangial conceptacles. Previous molecular studies based on SSU rDNA sequences and including an isolate of ‘M. engelhartii’ from South Africa support the same view. It is shown that the name ‘Fam.Mesophylleae Dum.’ Heeg [1891. Niederösterreiehische Lebermoose.- Verhandl. der k.k. zool.-botan. Gesellsch. in Wien 41:567–573] in Leverworts is invalid. Hence Mesophyllaceae Athanasiadis [2016. Phycologia Europaea Rhodophyta, Vols 1 & 2. Published by the author, Gothenburg. xlviii + 1504 pages] is available in the Corallinales (including Hapalidiales), while Mesophyllumaceae Schneider & Wynne (2019. Fourth addendum to the synoptic review of red algal genera. Botanica Marina. 62:355–367) becomes a later synonym.

Detail description of Lithophyllum okamurae (Lithophylloideae, Corallinales), a widely distributed crustose coralline alga in marine ecosystems

Lithophyllum okamurae is one of the important encrusting coralline algae, which plays important roles as primary producer, carbonate sediment builder, and habitat provider in the marine ecosystems. In this study, L. okamurae was collected from tropical coast of Sanya, and firstly described based on both detailed morph-anatomical characteristics and molecular studies of typic DNA sequences. The structure of the thalli of L. okamurae was pseudoparenchymatous construction with radially organized dimerous organizations in the crustose portion. The pseudoparenchymatous construction were composed of three parts, including 1 to 3 layers of epithelia cells which had flatten to round outermost walls, one layer of square or rectangular cells of the hypothallia and multiple layers of square or elongated rectangular peripheral cells. Palisade cells were observed, and the cells of the contiguous vegetative filaments were connected by secondary pit-connections with cell fusions absent. The carposporangial conceptacles, the spermatangial conceptacles, the bisporangial conceptacles and the tetrasporangial conceptacles were observed, and all these four kinds of conceptacles were uniporate. The spermatangial conceptacles were slightly convex and buried at shallow depths in the thalli tissues, and the carposporangial conceptacles and asexual conceptacles were protruding and conical. Phylogenetic studies based on DNA barcoding markers of 18S rDNA, COI, rbcL and psbA revealed that L. okamurae clustered with the closest relation of L. atlanticum, and formed a distinct branch. Based on the comparative anatomical features and the molecular data, the detailed description of the valid species of L. okamurae was firstly given in this study to provide theoretical basis for algae resources utilization and conservation in marine ecosystems.

Newly discovered coralline algae in Southeast Brazil: Tectolithon fluminense gen. et sp. nov. and Crustaphytum atlanticum sp. nov. (Hapalidiales, Rhodophyta)

ABSTRACTTwo new Melobesioideae, Tectolithon fluminense gen. et sp. nov. and Crustaphytum atlanticum sp. nov., were described based on specimens collected at depths from 2 to 30 m in a tropical to subtropical transitional region of Southeast Brazil. Analyses of the plastid-encoded markers psbA and rbcL demonstrated that these taxonomic novelties belong to the clade formed by the typically subarctic/arctic Clathromorphum complex. Tectolithon fluminense has tetra/bisporangial and carposporangial conceptacles that typically become buried in the thallus because of an enveloping process caused by the development of a vegetative rim that grows from the margins of the conceptacle. The rim then fuses and creates a vegetative cover. The development of this vegetative cover is described in detail and its possible convergent evolution in other taxa is discussed. Crustaphytum atlanticum differed morpho-anatomically from the generitype, C. pacificum (the only other known species in this genus), by thallus thickness, maximum number of epithallial cell layers, relative size of subepithallial initials and tetra/bisporangial conceptacle chamber dimensions. The observation of specimens from Tectolithon and Crustaphytum with subepithallial initials that are both longer and shorter than their immediate inward derivatives indicates that this morpho-anatomical character should be used with caution for generic delimitation in the Melobesioideae.

The taxonomy of middle Miocene red algae from the Gârbova de Sus Formation (Transylvanian Basin, Romania)

This study describes seventeen non-geniculate coralline algal species (orders Corallinales, Hapalidiales and Sporolithales) from the middle Miocene (lower-middle Badenian) red-algal limestones of the Transylvanian Basin, Gârbova de Sus Formation. For the description and identification at species level, we follow the common diagnostic features used for fossil species and some characters that are used as diagnostic for modern species (roof morphology for asexual conceptacles, the presence/absence of a layer of elongated cells below sporangial compartments and number of cells in paraphyses for Sporolithon, and measurements of gametangial and carposporangial conceptacles). Female conceptacles of Spongites fruticulosus Kutzing are for the first time described in fossil material. We propose the attribution of Lithophyllum platticarpum Maslov to Spongites fruticulosus Kutzing as a gametangial thallus with male conceptacles.

New diagnostic characters for the order Sporolithales (Corallinophycidae, Rhodophyta).

The diagnosis of the order Sporolithales is currently restricted to tetrasporangial anatomy. Until recently, there were few reports about gametangial, and more specifically carposporangial material for the Sporolithales. This study provides the first detailed observations of the anatomy of the mature carposporophyte phase from three species of Sporolithales commonly found in rhodolith beds from Brazil: Sporolithon episporum, S.ptychoides, and Sporolithon sp. Using these observations, along with previously published descriptions and illustrations from other representative species in the order, a comparison was made with the other three orders (Corallinales, Hapalidiales, and Rhodogorgonales) of the Corallinophycidae. We amend the diagnosis of the order Sporolithales to include the anatomy of the mature carposporophyte as follows: carposporangial conceptacles that lack a central fusion cell, but instead with numerous, short, one to two-celled, filaments that bear oblong terminal carposporangia that are distributed across the conceptacle chamber floor and walls.

Diagnostic characters in fossil coralline algae (Corallinophycidae: Rhodophyta) from the Miocene of southern Moravia (Carpathian Foredeep, Czech Republic)

Fourteen coralline algal species (Corallinales, Sporolithales) from Early Langhian (Lower Badenian) red-algal limestones of the Carpathian Foredeep (Czech Republic) are described: Sporolithon lvovicum (Maslov) Bassi et al., Lithothamnion roveretoi Airoldi, Lithothamnion moretii Lemoine, ?Lithothamnion sp. 1, ?Lithothamnion sp. 2, Mesophyllum alternans (Foslie) Cabioch & Mendoza, M. cf. erubescens (Foslie) Lemoine, M. cf. printzianum Woelkerling & Harvey, M. curtum Lemoine, Phymatolithon sp., Lithophyllum sp. 1, Lithophyllum sp. 2, Hydrolithon lemoinei (Miranda) Aguirre et al. and Spongites fruticulosa Kützing. The characters used in coralline algal species description and identification are summarized and discussed. Five characters newly used in fossil material are associated with the structure and fate of presumed tetrasporangial, gametangial and carposporangial conceptacles, with the shape, size and organization of roof cells, and with the position of the asexuate conceptacles relative to the surrounding thallus surface. Gametangial conceptacles of Phymatolithon and gametangial and carposporangial plants of Sporolithon lvovicum are described for the first time.

A modern account of the South African non-geniculate Lithophylloideae (Corallinales, Corallinophycidae, Rhodophyta)

Of the genera within the coralline algal subfamily Lithophylloideae, the genera Lithophyllum and Titanoderma have probably been the most contentious in recent years. Two opposing taxonomic views currently exist. One view considers Titanoderma to be a heterotypic synonym of Lithophyllum, arguing that the morphological criteria proposed to separate the two genera do not stand up to rigorous testing. The other view, which is increasingly being supported by molecular data, considers Titanoderma and Lithophyllum to be distinct genera. Based on our study of numerous recently collected specimens and of detailed published accounts on the genera, we support the separation of Titanoderma from Lithophyllum as we found no difficulty in assigning species to either genus on the basis of the characters proposed to separate them. Three species of Lithophyllum (L. acrocamptum, L. incrustans, L. neoatalayense) and three species of Titanoderma (T. corallinae, T. polycephalum, T. pustulatum) are currently reported to occur in South Africa. Here we present detailed illustrated accounts of the species, including: first time detailed descriptions for South African T. corallinae and T. pustulatum; new data on female and carposporangial conceptacles; and comparisons from other geographical locations where the same species have been described in detail. A key for identifying South African specimens is included. Our data support the characterisation of the genus Titanoderma separate from Lithophyllum.

Systematic position of Paulsilvella in the Lithophylloideae (Corallinaceae, Rhodophyta) confirmed by molecular data

New specimens of Paulsilvella huveorum were collected in Brazil at Baía de Ilha Grande, Rio de Janeiro, and Sebastião Gomes reef, Bahia. This new collections represent a relevant range extension and new hosts for the species (Amphiroa beauvoisii, Jania cubensis and non-identified Hydrozoa and Bryozoa) and enabled the first DNA amplifications for Paulsilvella. The systematic position of Pausilvella in the subfamily Lithophylloideae is confirmed based on SSU rDNA, psbA and rbcL molecular markers. Morphologically and anatomically the specimens are similar to the original description in where basal dimerous thalli with monomeric erect branches characterize the genus. But, the analyzed carposporangial conceptacles express the roof position varying from flush or above the thallus surface, the chambers always buried within tiers of columnar cells, suggesting that this feature is variable within the species and might also suggest that P. huveorum and the fossil P. antiqua should be considered as potential synonyms. We do not want to suggest this clump waiting for more collections from different geographical areas in where new data may support our idea. Our results strongly suggest that the subfamily Lithophylloideae urgently needs to be reviewed to delimit genera based on molecular and morphological analysis because monomeric and dimeric thalli organization have evolved several times in the group.

The genera Melyvonnea gen. nov. and Mesophyllum s.s. (Melobesioideae, Corallinales, Rhodophyta) particularly from the central Atlantic Ocean

We propose the new genus Melyvonnea to accommodate species previously included in Mesophyllum having: a) perithallial protuberances that may branch and dominate over the encrusting base, b) monoecious gametophytes with gametangial conceptacles occasionally developed in superimposition, c) spheroid carposporangial chambers (lacking a central pedestal), and d) filaments lining canals of multiporate roofs composed of 3 to 5 cells with distinctively elongate basal cells. The new genus shares with Mesophyllum the development of a predominantly coaxial hypothallium. Melyvonnea presently accommodates three species in the Central Atlantic, viz. the generitype Melyvonnea canariensis (Foslie) comb. nov. from the Canary Islands, Melyvonnea erubescens (Foslie) comb. nov. ( = Mesophyllum incertum; type locality: Bermuda) from the western Atlantic, Melyvonnea aemulans (Foslie & Howe) comb. nov. from Puerto Rico, and one Indo‐Pacific species, Melyvonnea madagascariensis (Foslie) comb. nov. We also emend Mesophyllum Lemoine to encompass Northern Hemisphere species that lack the above apomorphies of Melyvonnea and in addition develop a central pedestal in carposporangial conceptacles (via dissolution of the surrounding cells) with gonimoblasts bending down to fill the empty space. Mesophyllum sensu stricto currently includes six species in the northeast Pacific (M. aleuticum, M. conchatum, M. crassiusculum, M. lamellatum, M. megagastri, M. vancouveriense), two species in the western Atlantic (M. mesomorphum and M. syntrophicum), and three species in the northeast Atlantic and the Mediterranean Sea (M. expansum, M. lichenoides, M. philippii). Gametophytic species of each genus show a mainly disjunct distribution being restricted to the tropics–subtropics (Melyvonnea) and the temperate waters of the Northern Hemisphere (Mesophyllum s.s.). This classification is supported by a consensus of studies of all well‐known species of Mesophyllum sensu Adey (1970), and is based on a phylogenetic analysis of morphological and anatomical characters in addition to molecular evidence.

Development of conceptacles in Amphiroa (Corallinales, Rhodophyta)

Here, we describe the development of sporangial and gametangial conceptacles for Amphiroa beauvoisii and A. vanbosseae; sporangial conceptacles only for A. misakiensis; and gametangial conceptacles only for A. cryptarthrodia and A. rigida. The descriptions are based on the observation of histological preparations obtained from 112 specimens collected from the Gulf of California, in Mexico, and the Azores archipelago of Portugal. Information on the development of the sporangial conceptacle pore and conceptacle senescence is here described and illustrated for the first time. Four development patterns were observed: two for sporangial conceptacles; one for spermatangial conceptacles; and one for carposporangial conceptacles. The phases of development of the sporangial conceptacle were found to be useful in delimiting species within the genus. Based on the sporangium location on the cavity floor and the pore canal anatomy, the species A. beauvoisii, A. misakiensis and A. vanbosseae can be distinguished from each other.

First Record ofSporolithon ptychoidesHeydrich (Sporolithales, Corallinophycidae, Rhodophyta) from Thailand

Sporolithon ptychoides Heydrich (Sporolithaceae, Sporolithales), the type species of the genus Sporolithon, is newly reported for Thai waters based on specimens collected from the Gulf of Thailand and the Andaman Sea. A detailed morphological and anatomical account is provided, including comparisons with published data of S. ptychoides and its related species. Epithallial cells are flared. Cells of adjacent filaments connect laterally mostly by secondary pit connections. Tetrasporangia are grouped in sori that occur in patches over the thallus surface. Sori are buried in distinct rows in the thallus. Details of male, female and carposporangial conceptacles of S. ptychoides are described for the first time. Gametangial thalli are monoecious with spermatangia and carposporangia born in uniporate conceptacles. Dendroid spermatangial branches occur on the floor, walls and roof of the male conceptacle chamber. Carpogonial branch consists of a hypogenous cell and a carpogonium. Central fusion cell is absent on the floor of the carposporangial conceptacle chamber.

MESOPHYLLUM SPHAERICUM SP. NOV. (CORALLINALES, RHODOPHYTA): A NEW MAËRL-FORMING SPECIES FROM THE NORTHEAST ATLANTIC(1).

Mesophyllum sphaericum sp. nov. is described based on spherical maërl individuals (up to 10 cm) collected in a shallow subtidal maërl bed in Galicia (NW Spain). The thalli of these specimens are radially organized, composed of arching tiers of compact medullary filaments. Epithallial cells have flattened to rounded outermost walls, and they occur in a single layer. Subepithallial initials are as long as, or longer than the daughter cells that subtend them. Cell fusions are abundant. Multiporate asexual conceptacles are protruding, mound-like with a flattened pore plate, lacking a peripheral raised rim. Filaments lining the pore canal and the conceptacle roof are composed of five to six cells with straight elongate and narrow cells at their base. Carposporangial conceptacles are uniporate, protruding, and conical. Spermatangial conceptacles were not observed. Molecular results placed M. sphaericum near to M. erubescens, but M. sphaericum is anatomically close to M. canariense. The examination of the holotype and herbarium specimens of M. canariense indicated that both species have pore canal filaments with elongate basal cells, but they differ in number of cells (five to six in M. sphaericum vs. four in M. canariense). Based on the character of pore canal filaments, M. canariense shows similarities with M. erubescens (three to five celled). The outermost walls of epithallial cells of M. canariense are flared compared to the round to flattened ones of M. erubescens, the latter being widely accepted for the genus Mesophyllum. The addition of M. sphaericum as new maërl-forming species suggests that European maërl beds are more biodiverse than previously understood.

Three species of Mastophora (Rhodophyta: Corallinales, Corallinaceae) in the tropical Indo-Pacific Ocean: M. rosea (C. Agardh) Setchell, M. pacifica (Heydrich) Foslie, and M. multistrata sp. nov.

Keats D.W., Maneveldt G.W., Baba M., Chamberlain Y.M. and Lewis J.E. 2009. Three species of Mastophora (Rhodophyta: Corallinales, Corallinaceae) in the tropical Indo-Pacific Ocean: M. rosea (C. Agardh) Setchell, M. pacifica (Heydrich) Foslie, and M. multistrata, sp. nov. Phycologia 48: 404–422. DOI: 10.2216/08-101.1.Three species of Mastophora (Corallinaceae, Corallinales, Rhodophyta) were found in extensive studies of non-geniculate coralline algae in various areas of the tropical Indo-Pacific, including French Polynesia, Fiji, Ryukyu Islands (Japan), and Taiwan. Two species are delicate and leafy but are distinguishable on morphological grounds. Mastophora rosea plants are taeniform, dichotomously branched, and weakly calcified and have rolled margins. Their thalli show very little secondary growth, with only occasional small round patches at the surface. Tetrasporangial and carposporangial conceptacles are very high (330–640 μm) and dome-shaped to almost spherical. Mastophora rosea plants collected during this study stand out in the water because of their bluish-purple colour. Mastophora pacifica has more strongly calcified thalli that are irregularly branched, with abundant secondary growth and the development of loosely attached, crispy layers. Tetrasporangial and carposporangial conceptacles are conical (280–550 μm high). Thallus colour in M. pacifica varies substantially depending on where it is growing, ranging from violet brown to dark red to greyish ruby, but are mostly pale-pink to reddish-purple in their submerged living state. Mastophora multistrata sp. nov. plants are hard and robust. Their thalli are made up of tightly packed layers that are evident only in section. Tetrasporangial conceptacles are generally low (315–490 μm high) and dome-shaped. In their living state, M. multistrata plants are usually deep-purple plum coloured.

The genus Leptophytum (Melobesioideae, Corallinales, Rhodophyta) on the Pacific coast of North America

A. Athanasiadis and W.H. Adey. 2006. The genus Leptophytum (Melobesioideae, Corallinales, Rhodophyta) on the Pacific coast of North America. Phycologia 45: 71–115. DOI: 10.2216/04-38.1We provide a first account of the genus Leptophytum on the Pacific coast of North America, after re-examining the types and representative collections of species previously associated with Leptophytum, Mesophyllum and Lithothamnion of the Melobesioideae. Six species are recognized, distributed between Alaska (Port Clarence) and Baja California (Isla Magdalena), viz.: Leptophytum tenue (Kjellman) comb. nov. from Port Clarence and Orcas Island in Puget Sound (Washington State), L. adeyi from Tatoosh Island (Washington State), L. lamellicola sp. nov. from California (Monterey and San Mateo Counties) and southern Vancouver Island, L. julieae sp. nov. from SW and SE Vancouver Island and the Queen Charlotte Islands, L. foecundum var. sandrae var. nov. from southern Vancouver Island and Seattle (the typical variety foecundum being restricted to the Arctic and North Atlantic Oceans), and L. microsporum (Foslie) comb. nov. from southern California (Santa Catalina I.) to Baja California (Isla Magdalena). All species display the following characters, which unite them with North Atlantic congeners: noncoaxial (or predominantly noncoaxial) hypothallium, flattened epithallial cells, shedding conceptacles, and no perithallial protuberances. Sexual species (L. lamellicola and L. tenue in the North Pacific, and L. laeve and L. elatum in the North Atlantic) develop predominantly simple spermatangial mother cells with few branched ones occurring centrally or in other places on the chamber floor. Chambers of carposporangial conceptacles display a flattened floor with peripheral development of carposporangia. The NE Pacific species differ from each other in: (1) thallus adhesion (L. lamellicola and L. julieae grow partly unattached), (2) hypothallial growth (patches of coaxial cells occur regularly in L. lamellicola and less frequently in L. foecundum, L. tenue and L. microsporum), (3) perithallial stratification (present in L. lamellicola, L. julieae and L. foecundum), (4) size of subepithallial meristematic cells (distinctively elongateovate in L. julieae), (5) embedded multiporate conceptacles (present in L. lamellicola, L. julieae and L. microsporum), and (6) pore cell morphology of multiporate conceptacles. Each taxon is formally described, and its features are illustrated, tabulated and discussed. A dichotomous key to the six NE Pacific species is also provided together with an emended generic description that encompasses nine Northern and three Southern Hemisphere species.

Lithophyllum cuneatum sp. nov. (Corallinaceae, Rhodophyta), a new species of non‐geniculate coralline alga semi‐endophytic in Hydrolithon onkodes and Neogoniolithon sp. from Fiji, South Pacific

SUMMARYA new species of semi‐endophytic coralline alga, Lithophyllum cuneatum (Corallinaceae: Lithophylloideae), is described from Fiji. The species is characterized by a wedge‐like thallus that is partially buried in the thallus of the host coralline, Hydrolithon onkodes (Heydrich) Penrose et Woelkerling or occasionally Neogoniolithon sp., and that appears at the surface of the host as a small pustule that is usually paler in color than the host. The thallus consists of erect filaments that are derived from a single cell. The basal cell, when visible, is non‐palisade, and areas of bistratose margin are absent. Cells of contiguous erect filaments are joined by secondary pit connections. Epithallial cells are present in 2–3 layers, and individual trichocytes are common. Gametangial plants are dioecious. Male conceptacles have simple spermatangial systems that are confined to the floors of their elliptical chambers. Carposporangial conceptacles contain 5–8 celled gonimoblast filaments that are borne at the margin of a more‐or‐less discoid fusion cell, and so occupy the periphery of the elliptical conceptacle chambers. Tetrasporangial conceptacles are uniporate, with roofs formed from peripheral filaments, and chambers lack a central columella of sterile filaments. Despite its semi‐endophytic nature, haustorial cells are absent, and plastids and pigmentation are present.

The melobesioid alga Mesophyllum engelhartii (Rhodophyta, Corallinaceae) in South Africa

Mesophyllum engelhartii is a crustose coralline, melobesioid, red alga that is common in the Western Cape province and parts of the Eastern Cape province but becomes rare in KwaZulu-Natal. It occurs mainly on rocks and shells in the low intertidal and subtidal zones. The principal characters defining the species are the slightly to markedly prominent conceptacles and the structure of the tetra/bisporangial pore plate that is composed (in vertical section) of 4–6 somewhat elongate cells that are similar throughout and not specialized either in the conceptacle rim or in cells adjacent to pores. The following type specimens, described by Foslie on the basis of South African material, are shown to be conspecific with M. engelhartii : the lectotype and isolectotype of Lithothamnion discrepans , and the holotype of Lithothamnion synanablastum f. speciosa. The isotype of Goniolithon elatocarpum is probably also conspecific but bears only non-diagnostic carposporangial conceptacles. As the epithet engelhartii has nomenclatural priority, the other taxa are now subsumed in Mesolphyllum engelhartii which is a common southern Australian species.

Hydrolithon cymodoceae (Foslie) comb. nov. (Corallinaceae, Rhodophyta) in southern Australia and its relationships to Fosliella

An examination of southernAustralian populations of Hydrolithon cymodoceae (Foslie) comb. nov. (Basionym: Melobesia cymodoceae Foslie) (Corallinaceae, Rhodophyta) has shown that plants vary considerably in thallus thickness. Tetrasporangial conceptacles have pore canals lined by a ring of conspicuous, elongate cells that arise from filaments interspersed amongst sporangial initials, do not protrude into the canal, and are oriented more or less perpendicularly to the thallus surface. These conceptacle features are considered diagnostic of Hydrolithon, and thus the species has been transferred into this genus. In addition, the species shows a number of distinctive features associated with reproduction. Tetrasporangial conceptacles usually contain a single zonately divided tetrasporangium lying horizontally within the chamber. Irregularly divided tetrasporangia, bisporangia, and undivided sporangia resembling monosporangia are also sometimes formed. Carposporangial conceptacles contain a single carposporangium that may develop directly from an ovoid-shaped fusion cell, and the pore canal is oriented obliquely to the thallus surface. A detailed morphological and anatomical account of H. cymodoceae is provided, its relationships to Fosliella are discussed, and relevant nomenclatural data are included.