Fertile Gametophytes Research Articles

Effects of thermal history on reproductive success and cross-generational effects in the kelp Laminaria pallida (Phaeophyceae)

As climate change threatens marine ecosystems, sessile species such as kelps can be particularly impacted by rapidly changing environmental conditions. In this context, phenotypic plasticity can allow organisms to optimize their performance to cope with high temperatures. Here, we investigated the effects of thermal history on reproductive success and cross-generational plasticity in the warm-temperate kelp Laminaria pallida. Our results show that reproductive success of fertile gametophytes (14ºC) was improved by prior vegetative growth under warm compared to cold conditions. Cross-generational effects were evident; thermal tolerance of microscopic F1 sporophytes was modulated by the thermal history of the parental gametophytes. However, the effects were complex, varying by physiological trait, exposure time and genotype (crosses). A warm thermal history increased the photosynthetic efficiency of sporophytes at moderate to high temperatures, while the sporophytes from a cold thermal history grew more during the first 8 d at all experimental temperatures, but this effect disappeared over time. Our results suggest that preconditioning for reproduction and cross-generational effects can play an important role in the adaptation of L. pallida to warm habitats, highlighting the importance of incorporating thermal history effects in physiological studies to accurately predict the vulnerability of populations and species to future warming climates.

Low-Trunk Epiphytic Fern Gametophyte and Sporophyte Occurrence Is Influenced by Moss Height and Density in a Costa Rican Lowland Tropical Rain Forest

Premise of research. Tropical epiphytic ferns and mosses commonly inhabit similar niche spaces, yet little is known about the interspecific interactions between the two, especially with reference to the fern life cycle of functionally distinct, independent gametophytes and sporophytes. Previous research has shown that mosses often act as ecosystem engineers, storing water and altering the microclimate to allow seed plant establishment. And because ferns require free water for gamete exchange, mosses may play an important facilitative role in fern fertilization. In our study, we examine the spatial relationships between low-trunk epiphytic mosses, fern gametophytes, and sporophytes in a lowland tropical rain forest in Costa Rica.Methodology. We surveyed low-trunk (0–2 m above the forest floor) epiphytic ferns at La Selva Biological Station and compared the height (average of five tallest ramets) and density (classified into four classes based on percentage of cover) of mosses near fern gametophytes and fern sporophytes while considering the effects of other abiotic factors including light, azimuth, height on the tree, and tree diameter at breast height.Pivotal results. A logistic regression analysis of fern life stage against all measured abiotic and biotic factors revealed that only moss height predicted the occurrence of fern gametophytes or sporophytes. Fern gametophytes occurred in shorter moss, while fern sporophytes occurred in taller moss. As moss density increased, the percentage of sporophyte individuals increased, while the percentage of gametophytes decreased.Conclusions. Our data show evidence of a novel biotic mechanism that assists the success of ferns as epiphytes. The results indicate that tall moss, possibly through microclimatic properties, facilitates gametophyte fertilization or sporophyte survival but outcompetes fern gametophytes as the moss increases in height and density. Unraveling the interspecific interactions between these two dominant epiphyte lineages provides further insight into canopy successional processes, biotic interactions among epiphytes, and fern community ecology.

Leaflet initiation and blade expansion are separable in compound leaf development

Compound leaves are composed of multiple separate blade units termed leaflets. In tomato (Solanum lycopersicum) compound leaves, auxin promotes both leaflet initiation and blade expansion. However, it is unclear how these two developmental processes interact. With highly variable complexity, tomato compound leaves provide an ideal system to address this question. In this study, we obtained and analyzed mutants of the WUSCHEL-RELATED HOMEOBOX (WOX) family gene SlLAM1 from tomato, whose orthologs in tobacco (Nicotiana sylvestris) and other species are indispensable for blade expansion. We show that SlLAM1 is expressed in the middle and marginal domains of leaves, and is required for blade expansion in leaflets. We demonstrate that sllam1 mutants cause a delay of leaflet initiation and slightly alter the arrangement of first-order leaflets, whereas the overall leaflet number is comparable to that of wild-type leaves. Analysis of the genetic interactions between SlLAM1 and key auxin signaling components revealed an epistatic effect of SlLAM1 in determining the final leaf form. Finally, we show that SlLAM1 is also required for floral organ growth and affects the fertility of gametophytes. Our data suggest that SlLAM1 promotes blade expansion in multiple leaf types, and leaflet initiation can be largely uncoupled from blade expansion during compound leaf morphogenesis.

Flower morphogenesis and gametophyte fertility attest to the rare condition of gynomonoecy in Parietaria debilis (Urticaceae)

Parietaria debilis G. Forst. is gynomonoecious, which is a rare condition in the Urticaceae family and among angiosperms. Apetalous flowers of two different morph types (monoclinous, pistillate) occur in the same inflorescence and are reduced in size and in the number of whorls and of organs per whorl. The objective of this study was to compare the morphogenesis of monoclinous and pistillate flowers to determine whether the monoclinous flowers produce fertile gametophytes, and elucidate the pathways leading to the absence of stamens and to the changes in number of whorls and organs per whorl. Flower buds and flowers (non-fertilized, fertilized) were processed for surface and anatomical studies. Pollen ultrastructure and viability were determined. Inflorescences with fertilized flowers were checked for the presence and location of fruits/viable seeds. The monoclinous flower has four sepals, four stamens, and a uniovulate pseudomonomerous gynoecium. In the pistillate flower, the stamens are absent or, rarely, aborted. No petals are formed. The gynoecium is pseudomonomerous, originated as a central primordium that differentiates into two carpels, but only one develops and houses an ovule. Monoclinous and pistillate flowers produce viable seeds. Thus, our data confirmed that this species is indeed gynomonoecious.

Morphological, genotypic and metabolomic signatures confirm interfamilial hybridization between the ubiquitous kelps Macrocystis (Arthrothamnaceae) and Lessonia (Lessoniaceae)

Macrocystis pyrifera and Lessonia spicata are economically and ecologically relevant brown seaweeds that recently have been classified as members of two separated families within Laminariales (kelps). Here we describe for the first time the Macrocystis pyrifera x Lessonia spicata hybridization in the wild (Chiloe Island, Southeastern Pacific), where populations of the two parents exist sympatrically. Externally, this hybrid exhibited typical features of its parents M. pyrifera (cylindrical and flexible distal stipes, serrate frond margins and presence of sporophylls) and L. spicata (rigid and flat main stipe and first bifurcation), as well as intermediate features between them (thick unfused haptera in the holdfast). Histological sections revealed the prevalence of mucilage ducts within stipes and fronds (absent in Lessonia) and fully developed unilocular sporangia in the sporophylls. Molecular analyses confirmed the presence of the two parental genotypes for ITS1 nrDNA and the M. pyrifera genotype for two predominantly maternally inherited cytoplasmic markers (COI and rbcLS spacer) in the tissue of the hybrid. A metabolome-wide approach revealed that this hybrid is more chemically reminiscent to M. pyrifera. Nevertheless, several hits were identified as Lessonia exclusive or more remarkably, not present in any of the parent. Meiospores developed into apparently fertile gametophytes, which gave rise to F1 sporophytes that reached several millimeters before suddenly dying. In-vitro reciprocal crossing of Mar Brava gametophytes from both species revealed that although it is rare, interfamilial hybridization between the two species is possible but mostly overcome by pseudogamy of female gametophytes.

Protein Phosphatase 2A B'α and B'β Protect Centromeric Cohesion during Meiosis I.

During meiosis, the stepwise release of sister chromatid cohesion is crucial for the equal distribution of genetic material to daughter cells, enabling generation of fertile gametophytes. However, the molecular mechanism that protects centromeric cohesion from release at meiosis I is unclear in Arabidopsis (Arabidopsis thaliana). Here, we report that the protein phosphatase 2A regulatory subunits B'α and B'β participate in the control of sister chromatid separation. The double mutant b'αβ exhibited severe male and female sterility, caused by the lack of a nucleus or presence of an abnormal nucleus in mature microspores and embryo sacs. 4',6-Diamidino-2-phenylindole staining revealed unequal amounts of DNA in the mononuclear microspores. Transverse sections of the anthers revealed unevenly sized tetrads with or without a nucleus, suggesting a defect in meiocyte meiosis. An analysis of chromosome spreads showed that the sister chromatids separated prematurely at anaphase I in b'αβ Immunoblotting showed that AtRECOMBINATION DEFECTIVE8 (AtREC8), a key member of the cohesin complex, was hyperphosphorylated in b'αβ anthers and pistils during meiosis but hypophosphorylated in the wild type. Furthermore, yeast two-hybrid and bimolecular fluorescence complementation assays showed that B'α and B'β interact specifically with AtREC8, AtSHUGOSHIN1 (AtSGO1), AtSGO2, and PATRONUS1. Given that B'α was reported to localize to the centromere in meiotic cells, we propose that protein phosphatase 2A B'α and B'β are recruited by AtSGO1/2 and PATRONUS1 to dephosphorylate AtREC8 at the site of centromere cohesion to shield it from cleavage until anaphase II, contributing to the balanced separation of sister chromatids at meiosis.

Size structure and dynamics of an invasive population of lineage 2 of Asparagopsis taxiformis (Florideophyceae) in the Alboran Sea

SUMMARYIn this study, we present basic population data of the red macroalga Asparagopsis taxiformis, widely recognized as invasive in the Mediterranean Sea. A 13‐month field study was carried out on a population located in southern Spain, addressing its phenology, population dynamics and demography. We further tested whether biomass variations were related to environmental variables at the study site. Gametophytes were present year‐round while tetrasporophytes were only found in spring and summer. Recruitment capacity and vegetative growth of the gametophytes are discussed as important modulators for the population structure and enhancers of its persistence. Thallus size‐time histograms revealed a high prevalence of small shoots that showed high mortality that was not related to self‐thinning. Biomass of A. taxiformis was higher from March to July. Vegetative growth was the main way the gametophyte population was maintained, although the presence of tetrasporophytes and fertile gametophytes in the field confirms that sexual reproduction also occurs. Its continuous and high recruitment, in terms of the number of smallest shoots, makes this southern population of A. taxiformis a source of future invasive populations due to the intensive maritime traffic in the region.

Protocol: genetic transformation of the fern Ceratopteris richardii through microparticle bombardment.

BackgroundThe inability to genetically transform any fern species has been a major technical barrier to unlocking fern biology. Initial attempts to overcome this limitation were based on transient transformation approaches or achieved very low efficiencies. A highly efficient method of stable transformation was recently reported using the fern Ceratopteris richardii, in which particle bombardment of callus tissue achieved transformation efficiencies of up to 72%. As such, this transformation method represents a highly desirable research tool for groups wishing to undertake fern genetic analysis.ResultsWe detail an updated and optimized protocol for transformation of C. richardii by particle bombardment, including all necessary ancillary protocols for successful growth and propagation of this species in a laboratory environment. The C. richardii lifecycle comprises separate, free-living gametophyte and sporophyte stages. Callus is induced from the sporophyte apex through growth on cytokinin-containing tissue culture medium and can be maintained indefinitely by sub-culturing. Transgene DNA is introduced into callus cells through particle bombardment, and stable genomic integration events are selected by regeneration and growth of T0 sporophytes for a period of 8 weeks on medium containing antibiotics. Selection of T1 transgenic progeny is accomplished through screening T1 gametophytes for antibiotic resistance. In many cases sexual reproduction and development of transgenic embryos requires growth and fertilization of gametophytes in the absence of antibiotics, followed by a separate screen for antibiotic resistance in the resultant sporophyte generation.ConclusionsGenetic transformation of C. richardii using this protocol was found to be robust under a broad range of bombardment and recovery conditions. The successful expansion of the selection toolkit to include a second antibiotic for resistance screening (G-418) and different resistance marker promoters increases the scope of transformations possible using this technique and offers the prospect of more complex analysis, for example the creation of lines carrying more than one transgene. The introduction of a robust and practicable transformation technique is a very important milestone in the field of fern biology, and its successful implementation in C. richardii paves the way for adoption of this species as the first fern genetic model.Electronic supplementary materialThe online version of this article (doi:10.1186/s13007-015-0080-8) contains supplementary material, which is available to authorized users.

First record of fertile gametophytes of Polysiphonia perforans (Ceramiales, Rhodophyta)

Abstract We report fertile gametophytes of Polysiphonia perforans for the first time in collections from the Mediterranean Sea. The occurrence of spermatangial axes replacing whole trichoblasts and four-celled carpogonial branches, in addition to the previously known features, such as the occurrence of four pericentral cells, the open connection between rhizoids and pericentral cells and the straight arrangement of tetrasporangia, allow us to confirm that the species belongs to the genus Polysiphonia.

Effect of nitrate fertilization of gametophytes of the kelp Undaria pinnatifida on growth and maturation of the sporophytes cultivated in Matsushima Bay, northern Honshu, Japan

In northern Japan, the early production of high-quality specimens of kelps Undaria pinnatifida prior to the outbreak of pinhole disease is needed. To address this need, we tested the effect of nitrate fertilization of gametophytes on the growth and maturation of sporophytes using experimental and control gametophytes derived from sporophytes cultivated in Matsushima Bay, northern Honshu, Japan. From mid-August to October 2008, experimental gametophytes were cultured on a rope indoors at a nitrate concentration of 1 mg/L at the optimal seawater temperature of 20 °C, whereas control gametophytes were cultured without the addition of nitrate in normal seawater at an average temperature of 23.5 °C during this period in the past 30 years. Next, the seedlings were cultivated in Matsushima Bay until March 2009. For the experimental kelps, the total length, stipe length, stipe width, sporophyll length, sporophyll width, and dry weight of the blade, midrib, and sporophyll increased significantly from December to January compared to those of control kelps. Matured sporophylls of the experimental kelps were more than those of the control kelps from early December to late January. Significant higher photosynthesis occurred at seawater temperatures of 10 and 15 °C, as well as higher uptake rates of NO3–N of the experimental kelps in December and January. These results show that nitrate fertilization of the gametophytes makes it possible to harvest the high-priced blade, midrib, and sporophyll in January, which is earlier than the traditional harvest date.

Cytological studies on meiosis and male gametophyte development in autotetraploid cucumber

With improved staining and chromosome preparation techniques, meiosis of pollen mother cells (PMCs) and male gametophyte development in autotetraploid cucumber (Cucumis sativus L.) was studied to understand the correlation between chromosomes behaviour and fertility. Various chromosome configurations, e.g. multivalent, quadrivalents, trivalents, bivalents and univalents were observed in most PMCs at metaphase I. Lagging chromosomes were frequently observed at anaphase in both meiotic divisions. In addition, chromosomes segregations were not synchronous and equal in some PMCs during anaphase II and telophase II. Dyads, triads, tetrads with micronuclei and polyads were observed at tetrad stage, and the frequencies of normal tetrad with four microcytes were only 55.4 %. The frequency of abnormal behaviour in each stage of meiosis was counted, and the average value was 37.2 %. The normal meiotic process could be accomplished to form the microspore tetrads via simultaneous cytokinesis. Most microspores could develop into fertile gametophytes with 2 cells and 3 germ pores through the following stages: single-nucleus early stage, single-nucleus late stage and 2-celled stage. The frequency of abnormalities was low during the process of male gametophyte development. The germination rate of pollen grains was 46.9 %. These results suggested that abnormal meiosis in PMCs was the reason for low pollen fertility in the autotetraploid cucumber.

Notes on the marine algae of the Bermudas. 11. More additions to the benthic flora and a phylogenetic assessment of Halymenia pseudofloresii (Halymeniales, Rhodophyta) from its type locality

Schneider C.W., Lane C.E. and Saunders G.W. 2010. Notes on the marine algae of the Bermudas. 11. More additions to the benthic flora and a phylogenetic assessment of Halymenia pseudofloresii (Halymeniales, Rhodophyta) from its type locality. Phycologia 49: 154–168. DOI: 10.2216/09-46.1This paper contains the first reports of Veleroa magneana in the Atlantic Ocean, Chylocladia schneideri outside of its type locality in Puerto Rico, and Verdigellas peltata and Cladocephalus luteofuscus from shallow water. Also reported are new northern limits of distribution for Chondria leptacremon, Dasya antillarum, Laurencia caraibica, Lomentaria corallicola, Myriogramme prostrata and Udotea caribaea as well as the first four mentioned. Fertile gametophytes are documented for Ptilothamnion speluncarum for the first time from the type locality. Molecular evidence shows that Halymenia pseudofloresii, a species with its type locality in Bermuda, is sister to Halymenia floresii, the generitype, in the present analysis. More critically, molecular data establish that H. pseudofloresii has a broad range of morphological variation encompassing that displayed by true H. floresii and bringing into question reports of the latter from Bermudian waters.

High throughput culture and gametogenesis induction of Laminaria japonica gametophyte clones

In anticipation of the application of a new sporeling-raising method using gametophyte clones to Laminaria commercial cultivation in China, techniques of mass culture and gametogenesis induction of L. japonica gametophyte clones were developed, as a mass of fertile gametophytes is a prerequisite for sporeling-raising with the new method. Gametophyte clones which were subjected to fed-batch culture exhibited a classical logistic growth curve. Growth rates decreased gradually after 2 months of culture, and were negatively correlated to cell density. UNOVA also showed that only cell density has a significant effect on the growth of gametophyte clones under the experimental conditions. Based on the dynamics models revealed, a culture strategy only directed at the control of cell density was adopted. By this strategy, a total of 36 kg wet weight from an initial weight of 0.75 kg was achieved after 3 months culture in 100 20-L bottles. The final average density reached 24 g L−1. For the subsequent gametogenesis induction, amplificatory male and female gametophyte clones were cut, mixed and cultured in bottles under the same conditions used in amplification except for a change of photoperiod from continuous irradiance to 10 h light: 14 h dark cycle. Egg discharge occurred 10 days after the mixed culture and increased gradually with the culture duration. Most gametophytes gave rise to sporophytes 20 days after induction. Large-scale culture of gametophyte clones and gametogenesis induction for commercial cultivation in 2003–2005 have been conducted successfully.

Early life stages of the South Pacific kelps Lessonia nigrescens and Lessonia trabeculata (Laminariales, Phaeophyceae) show recovery capacity following exposure to UV radiation

F. Tala, K. Véliz, I. Gómez, and M. Edding. 2007. Early life stages of the South Pacific kelps Lessonia nigrescens and Lessonia trabeculata (Laminariales, Phaeophyceae) show recovery capacity following exposure to UV radiation. Phycologia 46: 467–470. DOI: 10.2216/06-56.1This study examined the recovery capacity of early life stages of the South Pacific kelps Lessonia nigrescens and Lessonia trabeculata after exposure to artificial ultraviolet radiation (UV-B280–315 nm, UV-A315–400 nm). Spores (3 h postrelease) were exposed to different UV doses applied as daily pulses (0.5, 1, 2, 3, 4 h) during 6 days. Afterwards cultures were kept under PAR condition and fertility of gametophytes and formation of sporophytes measured up to day 45 (for L. nigrescens) and 65 (for L. trabeculata). The irradiation with UV-B radiation for 6 days strongly impaired spore germination: at biologically effective UV doses (BEDCaldwell > 2 kJ m−2; pulses > 2 h per day), complete mortality of the spores was observed. In contrast, spores irradiated with UV-A retained a germination capacity close to 80 and 70% under high doses (75 kJ m−2; 4 h per day). The surviving spores from both treatments exhibited a recovery during their further development as the fertility of gametophytes and formation of sporophytes increased with age of culture. In the intertidal L. nigrescens, fertility of gametophytes from spores irradiated with UV-B during 0.5 and 1 h per day was between 70 and 100% after 45 days. Treatments with UV-A did not affect markedly the fertility and production of sporophytes, as values were always between 80 and 100% after 45 days. In the subtidal L. trabeculata, recovery of cultures irradiated with UV-B and UV-A were lower, in particular the formation of sporophytes, as compared to L. nigrescens. Two major findings are outlined: (1) exposure of spores to UV-B radiation affects the further development of the life cycle, and (2) the surviving spores retained their viability and were able to complete the life history.

Effects of blue light on gametophyte development ofLaminaria japonica (Laminariales, Phaeophyta)

”Laminaria” gametophyte was greatly influenced by light in its growth and development. Using light-emitting diodes (LED) as blue and red light sources, we analyzed the light effect on gametophytes development of ”Laminaria japonica” Aresch. The gametophytes were obtained from zoospores collected in April, May, July, 2003 and September, 2004. We found that the growth of gametophytes was stimulated by increasing intensity of blue light (BL) and red light (RL) illumination, of which BL was obviously stronger than that of RL. The fertilization of gametophytes depended largely on BL, and only sufficient BL illumination could take the reproductive effect. In addition, we noticed that there was a significant difference in light responses for gametophytes developed from zoospore collected in different times. For zoospores released in April, under BL1 (73.90 μmol photons/m•s), the unicellular female gametophytes and multi-cellular male gametophytes produced eggs and sperms respectively, and further developed towards sporophytes. However, for gametophytes developed in May, July or September, they became multi-cellular and never formed oogonia or antheridia. It is believed that the ”Laminaria” sporangium maturation stage could affect the gametophytes reaction to BL under laboratory culture conditions. Therefore, cryptochrome- or phototropin-like BL photoreceptors is probably involved in BL-induced development of ”Laminaria” gametophytes.

Long-term copper mine waste disposal in northern Chile associated with gene flow disruption of the intertidal kelp Lessonia nigrescens

This study tests the general hypothesis that habitat disruption caused by the release of copper mine wastes in coastal waters has a negative impact on gene flow among populations of the kelp Lessonia nigrescens Bory. Hierarchical sampling was performed within continuous, undisturbed stands and at the northern and southern edges of a 40 km gap caused by mine wastes. Our results, based on RAPD markers, showed a strong genetic structure even in the absence of the disrupting effect of the mine wastes. No pattern of isolation by distance is apparent, however, which indicates that populations are at migration-drift disequilibrium, and suggests that most events of spore recruit- ment and/or gametophyte fertilization occur within a few metres. On the other hand, some long dis- tance dispersal is likely to occur, which prevents isolation by distance within the spatial scale of 40 km. When comparing continuous stands across the disrupted habitat, an increased genetic differ- entiation associated with the interruption of the species distribution was observed. A Multiple Corre- spondence Analysis (MCA) clearly separated the sampling units into 2 groups, each representing a separate stand. Other lines of evidence supporting the idea of genetic disruption came from the mean pairwise differentiation estimates (FST) and from the Analyses of Molecular Variance (AMOVA). Finally, the southern edge of the interruption in the distribution of L. nigrescens showed clear signals of a recent founding event, suggesting that northward recolonisation is currently occurring.

Cytological Studies on Microsporogenesis and Male Gametophyte Development in a Cucumis Allotriploid Derived from Cucumis hytivus*C. sativus

Microsporogenesis and male gametophyte development of a Cucumis allotriploid from meiosis of PMCs to mature pollen grains were studied using light microscopy. Variable chromosome configurations, e.g. univalents, bivalents, trivalents, quadrivalents, etc. were observed in most PMCs of the allotriploid at MI. Chromosome lagging and bridges at anaphase resulted from irregular chromosome separation and asynchronization between C and H genomes were frequently observed as well, which led to formation of polyads and inviable gametes. However, there were still some PMCs in which the normal meiotic process could be accomplished to form the microspore tetrads via simultaneous cytokinesis. The arrangement of microspores in the tetrads was tetrahedral. Among those microspores, part of them (10%) could develop into fertile gametophytes with 2 cells and 3 germ pores through the following stages: single-nucleus early stage, single-nucleus late stage, 2-celled stage after pollen mitosis. A few 3-celled pollens were also observed. But most other microspores (90%) were sterile stopped at single-nucleus stage. The low fertility of male gametophytes was confirmed by the weak stainability and low germination rate.

Effect of temperature and photon fluence rate on gametophytes and young sporophytes of Laminaria ochroleuca Pylaie

We analysed the effects of temperature and photon fluence rate on meiospore germination, growth and fertility of gametophytes, and growth of young sporophytes of Laminaria ochroleuca. Maximum percentages of germination (91–98%) were obtained at 15°C and 18°C, independent of photon fluence rate. Optimal development of female gametophyte and maximum fecundity and reproductive success of gametophytes occurred at 15°C and 18°C and at 20 and 40 µmol m–2 s–1. Maximum relative growth rate of young sporophytes after 2 weeks of culture was achieved under the same conditions. L. ochroleuca gametophytes cannot reproduce and growth of its sporophytes is not competitive at temperatures close to 10°C.

Sporophytes and Gametophytes of Polytrichaceae from the Campanian (Late Cretaceous) of Georgia, U. S. A.

A new genus and species (Eopolytrichum antiquum) of the moss family Polytrichaceae are described for fossil sporophyte capsules and associated gametophytes from the early Campanian (Late Cretaceous) Buffalo Creek Member of the Gaillard Formation in central Georgia, U.S.A. The capsules show diagnostic features of the Polytrichaceae but differ from those of all extant genera. The capsules are terete in cross section, somewhat dorsiventrally flattened, and have a swollen, asymmetrical apophysis and mammillose exothecium. Stomatal complexes, each surrounded by a ring of subsidiary cells, are confined to the apophysis. The operculum is tall and dome shaped, but the calyptra and beak of the operculum are not preserved. The remains of a peristomial membrane are present around the rim of the capsule after the operculum has dehisced, but peristome teeth are absent, and the epiphragm is retained in the operculum. Spores are alete, spherical, and echinulate. Associated sterile and fertile gametophytes have leaves wi...

Comparative studies on gametangial distribution and structure in species of Zonaria and Homoeostrichus (Dictyotales, Phaeophyceae) from Australia

A comparative study of fertile gametophytes has been carried out on six species of the Dictyotales from Australia. Patterns of gametangial distribution and structure are similar in Zonaria angustata, Zonaria diesingiana, Zonaria spiralis and Zonaria turneriana, but there are some marked differences apparent between both Homoeostrichus olsenii and Homoeostrichus sinclairii and the Zonaria species. Sterile cortical cells and mucilage between the cylindrical oogonia are characteristic of the indusiate female sori of Zonaria, which differ markedly from the comparable structures of H. olsenii, in which all cortical cells have been transformed into oogonia and the walls of adjacent oogonia are contiguous. In contrast, the large spherical oogonia of H. sinclairii are unique in the Dictyotales, lacking a stalk cell and occurring among brown paraphyses in a large non-indusiate sorus on each terminal branch segment. Antheridial sori of the six species exhibit far less structural variation than the oogonial sori. Male sori are surrounded by undifferentiated cortical cells in H. olsenii, by tall brown paraphyses and short paraphyses in H. sinclairii and by sterile cells in Zonaria spp. Short paraphyses form only around the male sori of H. sinclairii in the Dictyotales; they differ in structure from the brown paraphyses but are similar to the antheridia, from which they may have been derived. Gametangial characters have proved invaluable in defining the genus Zonaria and in separating H. olsenii from H. sinclairii, but they cannot be used to delimit the species of Zonaria. Furthermore, the differences observed in the gametangia have provided new characters for phylogenetic analyses, as well as providing further supporting evidence for the recognition of Zonaria and Homoeostrichus as distinct entities.