Zygospore Formation Research Articles

Zygospore formation in Zygnematophyceae predates several land plant traits.

Recent research on a special type of sexual reproduction and zygospore formation in Zygnematophyceae, the sister group of land plants, is summarized. Within this group, gamete fusion occurs by conjugation. Zygospore development in Mougeotia, Spirogyra and Zygnema is highlighted, which has recently been studied using Raman spectroscopy, allowing chemical imaging and detection of changes in starch and lipid accumulation. Three-dimensional reconstructions after serial block-face scanning electron microscopy (SBF-SEM) or focused ion beam SEM (FIB-SEM) made it possible to visualize and quantify cell wall and organelle changes during zygospore development. The zygospore walls undergo strong modifications starting from uniform thin cell walls to a multilayered structure. The mature cell wall is composed of a cellulosic endospore and exospore and a central mesospore built up by aromatic compounds. In Spirogyra, the exospore and endospore consist of thick layers of helicoidally arranged cellulose fibrils, which are otherwise only known from stone cells of land plants. While starch is degraded during maturation, providing building blocks for cell wall formation, lipid droplets accumulate and fill large parts of the ripe zygospores, similar to spores and seeds of land plants. Overall, data show similarities between streptophyte algae and embryophytes, suggesting that the genetic toolkit for many land plant traits already existed in their shared algal ancestor. This article is part of the theme issue 'The evolution of plant metabolism'.

Zygospores of the green alga Spirogyra: new insights from structural and chemical imaging.

Zygnematophyceae, a class of streptophyte green algae and sister group to land plants (Embryophytes) live in aquatic to semi-terrestrial habitats. The transition from aquatic to terrestrial environments requires adaptations in the physiology of vegetative cells and in the structural properties of their cell walls. Sexual reproduction occurs in Zygnematophyceae by conjugation and results in the formation of zygospores, possessing unique multi-layered cell walls, which might have been crucial in terrestrialization. We investigated the structure and chemical composition of field sampled Spirogyra sp. zygospore cell walls by multiple microscopical and spectral imaging techniques: light microscopy, confocal laser scanning microscopy, transmission electron microscopy following high pressure freeze fixation/freeze substitution, Raman spectroscopy and atomic force microscopy. This comprehensive analysis allowed the detection of the subcellular organization and showed three main layers of the zygospore wall, termed endo-, meso- and exospore. The endo- and exospore are composed of polysaccharides with different ultrastructural appearance, whereas the electron dense middle layer contains aromatic compounds as further characterized by Raman spectroscopy. The possible chemical composition remains elusive, but algaenan or a sporopollenin-like material is suggested. Similar compounds with a non-hydrolysable character can be found in moss spores and pollen of higher plants, suggesting a protective function against desiccation stress and high irradiation. While the tripartite differentiation of the zygospore wall is well established in Zygnematopyhceae, Spirogyra showed cellulose fibrils arranged in a helicoidal pattern in the endo- and exospore. Initial incorporation of lipid bodies during early zygospore wall formation was also observed, suggesting a key role of lipids in zygospore wall synthesis. Multimodal imaging revealed that the cell wall of the sexually formed zygospores possess a highly complex internal structure as well as aromatics, likely acting as protective compounds and leading to impregnation. Both, the newly discovered special three-dimensional arrangement of microfibrils and the integration of highly resistant components in the cell wall are not found in the vegetative state. The variety of methods gave a comprehensive view on the intricate zygospore cell wall and its potential key role in the terrestrial colonization and plant evolution is discussed.

Induction of Conjugation and Zygospore Cell Wall Characteristics in the Alpine Spirogyra mirabilis (Zygnematophyceae, Charophyta): Advantage under Climate Change Scenarios?

Extreme environments, such as alpine habitats at high elevation, are increasingly exposed to man-made climate change. Zygnematophyceae thriving in these regions possess a special means of sexual reproduction, termed conjugation, leading to the formation of resistant zygospores. A field sample of Spirogyra with numerous conjugating stages was isolated and characterized by molecular phylogeny. We successfully induced sexual reproduction under laboratory conditions by a transfer to artificial pond water and increasing the light intensity to 184 µmol photons m−2 s−1. This, however was only possible in early spring, suggesting that the isolated cultures had an internal rhythm. The reproductive morphology was characterized by light- and transmission electron microscopy, and the latter allowed the detection of distinctly oriented microfibrils in the exo- and endospore, and an electron-dense mesospore. Glycan microarray profiling showed that Spirogyra cell walls are rich in major pectic and hemicellulosic polysaccharides, and immuno-fluorescence allowed the detection of arabinogalactan proteins (AGPs) and xyloglucan in the zygospore cell walls. Confocal RAMAN spectroscopy detected complex aromatic compounds, similar in their spectral signature to that of Lycopodium spores. These data support the idea that sexual reproduction in Zygnematophyceae, the sister lineage to land plants, might have played an important role in the process of terrestrialization.

Cell wall characteristics during sexual reproduction of Mougeotia sp. (Zygnematophyceae) revealed by electron microscopy, glycan microarrays and RAMAN spectroscopy

Mougeotia spp. collected from field samples were investigated for their conjugation morphology by light-, fluorescence-, scanning- and transmission electron microscopy. During a scalarifom conjugation, the extragametangial zygospores were initially surrounded by a thin cell wall that developed into a multi-layered zygospore wall. Maturing zygospores turned dark brown and were filled with storage compounds such as lipids and starch. While M. parvula had a smooth surface, M. disjuncta had a punctated surface structure and a prominent suture. The zygospore wall consisted of a polysaccharide rich endospore, followed by a thin layer with a lipid-like appaerance, a massive electron dense mesospore and a very thin exospore composed of polysaccharides. Glycan microarray analysis of zygospores of different developmental stages revealed the occurrence of pectins and hemicelluloses, mostly composed of homogalacturonan (HG), xyloglucans, xylans, arabino-galactan proteins and extensins. In situ localization by the probe OG7-13AF 488 labelled HG in young zygospore walls, vegetative filaments and most prominently in conjugation tubes and cross walls. Raman imaging showed the distribution of proteins, lipids, carbohydrates and aromatic components of the mature zygospore with a spatial resolution of ~ 250 nm. The carbohydrate nature of the endo- and exospore was confirmed and in-between an enrichment of lipids and aromatic components, probably algaenan or a sporopollenin-like material. Taken together, these results indicate that during zygospore formation, reorganizations of the cell walls occured, leading to a resistant and protective structure.

New observations on the sexual and asexual reproductive stages of Staurastrum gracile (Desmidiaceae, Zygnematophyceae)

ABSTRACT Staurastrum gracile is a highly polymorphic species that overlaps morphologically with other species of the genus. The observation of some reproductive features, such as zygospore development, is necessary for correct identification of some Staurastrum species. This study describes the sexual and asexual reproduction of S. gracile in culture and emphasises the importance of characters observed in the fully developed stage of vegetative individuals and zygospores. The description of the life cycle is based on isolated populations from Mexico studied in light and scanning electron microscopy. We describe morphology in the asexual reproductive stages, resulting from an early division before complete cell development, but also results from the number (3, 4, or 7), the length, and the plane of projection of the arms (divergent, moderately divergent to straight, and slightly convergent). We describe gamete fusion type in S. gracile and establish that meiosis occurs in early stages of zygospore formation, characterising the morphology of all stages until germination. The phylogenetic position of the Mexican populations was confirmed by sequence analysis of the ATPase beta-subunit gene (atpB), and the resulting phylogeny was compared with zygospore characters of species. The result suggests that zygospore morphology can be a significant phylogenetic signal in desmid taxonomy.

Molecular and morphological diversity of Zygnema and Zygnemopsis (Zygnematophyceae, Streptophyta) from Svalbard (High Arctic)

ABSTRACTFilamentous conjugating green microalgae (Zygnematophyceae, Streptophyta) belong to the most common primary producers in polar hydro-terrestrial environments such as meltwater streamlets and shallow pools. The mats formed by these organisms are mostly composed of sterile filaments with Zygnema morphology, but the extent of their diversity remains unknown. Traditional taxonomy of this group is based on reproductive morphology, but sexual reproduction (conjugation and formation of resistant zygospores) is very rare in extreme conditions. In the present study we gave the first record of zygospore formation in Svalbard field samples, and identified conjugating filaments as Zygnemopsis lamellata and Zygnema cf. calosporum. We applied molecular phylogeny to study genetic diversity of sterile Zygnema filaments from Svalbard in the High Arctic. Based on analysis of 143 rbcL sequences, we revealed a surprisingly high molecular diversity: 12 Arctic Zygnema genotypes and one Zygnemopsis genotype were found. In addition, we characterized individual Arctic genotypes based on cell width and chloroplast morphology using light and confocal laser scanning microscopy. Our findings highlight the importance of a molecular approach when working with sterile filamentous Zygnematophyceae, as hidden diversity might be very beneficial for adaptation to harsh environmental conditions, and experimental results could be misinterpreted when hidden diversity is neglected.

Two new species of Conidiobolus occurring in Anhui, China

Two new species of Conidiobolus were isolated from Anhui Province, China. A polyphasic taxonomic approach comprising morphological characteristics and molecular data (the nuclear large subunit of ribosomal DNA and the translation elongation factor 1 alpha gene sequences) was applied to determine their novel taxonomic status in the genus Conidiobolus. The new species C. mirabilis is a sister group to C. thromoides, but morphologically differs by smaller primary conidia and a unique formation of zygospores among two to four adjacent hyphal segments. The other new species C. pachyzygosporus characterized with thick-walled zygospores is phylogenetically closely related to C. antarcticus, C. couchii, and C. osmodes.

Identification of a new mating group and reproductive isolation in the Closterium peracerosum-strigosum-littorale complex.

Reproductive isolation is essential for the process of speciation. In order to understand speciation, it is necessary to compare one mating group with other phylogenetically related but reproductively isolated groups. The Closterium peracerosum-strigosum-littorale (C. psl.) complex is a unicellular isogamous zygnematophycean alga, which is believed to share a close phylogenetic relationship with the land plants. In this study, we identified a new mating group, named group G, of C. psl. complex and compared its physiological and biochemical characteristics with the mating group I-E, which was closely related to the mating group G. Zygospores are typically formed as a result of conjugation between mating-type plus (mt+) and mating-type minus (mt-) cells in the same mating group during sexual reproduction. Crossing experiments revealed mating groups G and I-E were reproductively isolated from each other, but the release of lone protoplasts from mt- cells of mating group G was induced in the presence of mt+ cells of mating group I-E. In fact, the sex pheromone, protoplast-release-inducing protein of mating group I-E induced the release of protoplasts from mt- cells of mating group G. When mt+ and mt- cells of both mating groups I-E and G were co-cultured (multiple-choice matings), the zygospore formation of mating group G, but not that of mating group I-E, was inhibited. Based on these results, we propose a possible mechanism of reproductive isolation between the two mating groups and suggest the presence of sexual interference between mating group G and mating group I-E.

Morphological characterization of sex-deficient mutants of the homothallic zygomycete Zygorhynchus moelleri

Heterothallic zygomycetes consist of two mating types, named plus and minus, whereas in homothallic species the genetic information for both mating types is present in one individual and nucleus. Nevertheless, zygophores, specialized sexual hyphae, of homothallic species harbor a plus or minus identity in the sexual reaction. Because of the lack of knowledge about the molecular and genetic background of the sexual development in zygomycetes, we used UV mutagenesis to create sexual defective mutants of Zygorhynchus moelleri. Our aim was to provide a set of mutants, which are helpful to identify new genes involved in the sexual morphogenesis. The six mutants presented here are arrested in different stages of the sexual development. Two mutants UV139 and UV542 predominantly produce only zygophores, whereas in two other mutants UV44 and UV48 the formation of gametangial walls is inhibited. Mutant UV554 seems to be blocked in the zygospore formation, whereas in mutant UV112 the wall formation of the zygosporangium is inhibited. We additionally isolated one methionine auxotroph, mutant UV127, which is blocked in the sexual and asexual development at low methionine concentrations, revealing the importance of methionine in the developmental processes of Z. moelleri.

Zygomycetes in Vesicular Basanites from Vesteris Seamount, Greenland Basin--A New Type of Cryptoendolithic Fungi.

Fungi have been recognized as a frequent colonizer of subseafloor basalt but a substantial understanding of their abundance, diversity and ecological role in this environment is still lacking. Here we report fossilized cryptoendolithic fungal communities represented by mainly Zygomycetes and minor Ascomycetes in vesicles of dredged volcanic rocks (basanites) from the Vesteris Seamount in the Greenland Basin. Zygomycetes had not been reported from subseafloor basalt previously. Different stages in zygospore formation are documented in the studied samples, representing a reproduction cycle. Spore structures of both Zygomycetes and Ascomycetes are mineralized by romanechite-like Mn oxide phases, indicating an involvement in Mn(II) oxidation to form Mn(III,VI) oxides. Zygospores still exhibit a core of carbonaceous matter due to their resistance to degradation. The fungi are closely associated with fossiliferous marine sediments that have been introduced into the vesicles. At the contact to sediment infillings, fungi produced haustoria that penetrated and scavenged on the remains of fragmented marine organisms. It is most likely that such marine debris is the main carbon source for fungi in shallow volcanic rocks, which favored the establishment of vital colonies.

Confirmation of Neozygites floridana azygospore formation in two-spotted spider mite (Tetranychus urticae) in strains from tropical and temperate regions

Neozygites floridana is an obligate fungal pathogen of mites in the family Tetranychidae and is an important natural enemy of the two-spotted spider mite (Tetranychus urticae). Until now, information about the formation of azygospores remained to be fully confirmed. In this study, we document the formation of azygospores by a Brazilian N. floridana strain and the formation of azygospores and zygospores by a Norwegian N. floridana strain, both in the host T. urticae. Evidence of both zygosporogenesis and azygosporogenesis was also found in the same individual in the Norwegian stains. Further we report the presence of immature azygospores with 1–3 nuclei for the Norwegian strains, immature resting spores (probably azygospores) with 1–8 nuclei for the Brazilian strain, and mature resting spores with 2 nuclei for both the Norwegian and the Brazilian strains (azygo- or zygospores). Our observations suggest that the immature resting spore (prespore) of both strains begins in a multinucleate condition but that the nuclear number is reduced during maturation until mature resting spore is binucleate regardless of its origin as a zygospore or azygospore.

De novo transcriptome profiling uncovers a drastic downregulation of photosynthesis upon nitrogen deprivation in the nonmodel green alga Botryosphaerella sudeticus

BackgroundNeutral lipid storage is enhanced by nitrogen deprivation (ND) in numbers of green microalgal species. However, little is known about the metabolic pathways whose transcription levels are most significantly altered following ND in green microalgae, especially the nonmodel species.ResultsTo start gaining knowledge on this, we performed transcriptome profiling of the nonmodel green microalga Botryosphaerella sudeticus cells in response to ND. Transcriptome of B. sudeticus is de novo assembled based on millions of HiSEQ short sequence reads using CLC Genomics Workbench software. The resulting non-redundant ESTs are annotated based on the best hits generated from the BLASTX homology comparison against the “best” proteins in the model microalgae Chlamydomonas reinhardtii and Chlorella variabilis. By using a pathway-based approach according to KEGG databases, we show that ESTs encoding ribosomal proteins and photosynthetic functions are the most abundantly expressed ESTs in the rapidly growing B. sudeticus cells. We find that ESTs encoding photosynthetic function but not the ribosomal proteins are most drastically downregulated upon ND. Notably, ESTs encoding lipid metabolic pathways are not significantly upregulated. Further analyses indicate that chlorophyll content is markedly decreased by 3-fold and total lipid content is only slightly increased by 50%, consistent with the transcriptional profiling. On the other hand, carbon content and photosynthesis efficiency are only marginally decreased by 7% and 20%, respectively, indicating that photosynthesis is only slightly reduced upon drastic downregulation of photosynthetic ESTs and chlorophyll content upon ND. In addition, TAG content is found to be greatly increased by 50-fold, though total lipid content is only slightly increased by 1.5-fold.ConclusionsTaken together, our results suggest that light-harvesting proteins and chlorophylls are in excess in B. sudeticus. Degradation of excess photosynthesis proteins is most likely a mechanism for recycling of nitrogen-rich molecules to synthesize new proteins for preparation of gametogenesis and zygospore formation in adaptation and survival upon ND. Furthermore, our analyses indicate that TAG accumulation is largely attributed to the modification of other pre-existing lipid molecules, rather than de novo synthesis. We propose that this is likely an evolutionarily conserved mechanism in many green microalgae species.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-14-715) contains supplementary material, which is available to authorized users.

Phylogenetic lineages in Entomophthoromycota.

Entomophthoromycota is one of six major phylogenetic lineages among the former phylum Zygomycota. These early terrestrial fungi share evolutionarily ancestral characters such as coenocytic mycelium and gametangiogamy as a sexual process resulting in zygospore formation. Previous molecular studies have shown the monophyly of Entomophthoromycota, thus justifying raising the taxonomic status of these fungi to a phylum. Multi-gene phylogenies have identified five major lineages of Entomophthoromycota. In this review we provide a detailed discussion about the biology and taxonomy of these lineages: I) Basidiobolus (Basidiobolomycetes: Basidiobolaceae; primarily saprobic); II) Conidiobolus (Entomophthoromycetes, Ancylistaceae; several clades of saprobes and invertebrate pathogens), as well as three rapidly evolving entomopathogenic lineages in the family Entomophthoraceae centering around; III) Batkoa; IV) Entomophthora and allied genera; and V) the subfamily Erynioideae which includes Zoophthora and allied genera. Molecular phylogenic analysis has recently determined the relationships of several taxa that were previously unresolved based on morphology alone: Eryniopsis, Macrobiotophthora, Massospora, Strongwellsea and two as yet undescribed genera of Basidiobolaceae.

Zygospore formation between homothallic and heterothallic strains of Closterium

Zygospore formation in different strains of the Closterium peracerosum-strigosum-littorale complex was examined in this unicellular isogamous charophycean alga to shed light on gametic mating strains in this taxon, which is believed to share a close phylogenetic relationship with land plants. Zygospores typically form as a result of conjugation between mating-type plus (mt(+)) and mating-type minus (mt(-)) cells during sexual reproduction in the heterothallic strain, similar to Chlamydomonas. However, within clonal cells, zygospores are formed within homothallic strains, and the majority of these zygospores originate as a result of conjugation of two recently divided sister gametangial cells derived from one vegetative cell. In this study, we analyzed conjugation of homothallic cells in the presence of phylogenetically closely related heterothallic cells to characterize the reproductive function of homothallic sister gametangial cells. The relative ratio of non-sister zygospores to sister zygospores increased in the presence of heterothallic mt(+) cells, compared with that in the homothallic strain alone and in a coculture with mt(-) cells. Heterothallic cells were surface labeled with calcofluor white, permitting fusions with homothallic cells to be identified and confirming the formation of hybrid zygospores between the homothallic cells and heterothallic mt(+) cells. These results show that at least some of the homothallic gametangial cells possess heterothallic mt(-)-like characters. This finding supports speculation that division of one vegetative cell into two sister gametangial cells is a segregative process capable of producing complementary mating types.

Heterothallic mating inMucor irregularisand first isolate of the species outside of Asia

This study reports on the discovery of heterothallic mating in Mucor irregularis (formerly Rhizomucor variabilis var. variabilis) and it extends the range of this species from Asia to the United States. We report on a case of primary cutaneous mucormycosis, involving the forearms of a cotton farmer from North Carolina, in which the infection was cured using amphotericin B therapy. Intraspecific crosses between the North Carolina strain DUMC 150.04 and M. irregularis CBS 103.93, the ex-type strain of R. variabilis var. variabilis from China, resulted in the formation of abundant fertile zygospores. By way of contrast, interspecific crosses between the North Carolina isolate and the ex-neotype strain of M. hiemalis NRRL 3624 resulted in the formation of putative azygospores by M. irregularis DUMC 150.04.

Characterization and Molecular Cloning of Conjugation-Regulating Sex Pheromones in Homothallic Closterium

Conjugation-regulating pheromones were analyzed in homothallic Closterium for the first time. Members of the Closterium peracerosum-strigosum-littorale complex are unicellular charophycean algae in which there are two modes of zygospore formation: heterothallism and homothallism. A homothallic strain of Closterium (designation, kodama20) forms selfing zygospores via the conjugation of two sister gametangial cells derived from one vegetative cell. Conjugation-promoting and -suppressing activities, against cells at very low (1 x 10(2) cells ml(-1)) and normal (1 x 10(4) cells ml(-1)) cell density, respectively, were detected in the medium in which cells of a normal density had been cultured. Pheromone activities decreased to 20% after incubation at 60 °C for 10 min. The release and action of the pheromones was dependent on light. The culture medium was subjected to gel filtration, and both active substances had an apparent molecular mass of 17 kDa; this was similar to that previously reported for the heterothallic sex-specific pheromone protoplast-release-inducing protein (PR-IP) Inducer. cDNAs encoding the orthologs of PR-IP Inducer were isolated from the homothallic strain. Recombinant PR-IP Inducers produced by yeast cells showed conjugation-promoting activity. These results indicate that conjugation of the homothallic strain is regulated by an ortholog of a heterothallic sex-specific pheromone.

SEXUAL PROCESSES AND PHYLOGENETIC RELATIONSHIPS OF A HOMOTHALLIC STRAIN IN THECLOSTERIUM PERACEROSUM-STRIGOSUM-LITTORALECOMPLEX (ZYGNEMATALES, CHAROPHYCEAE)

Members of the Closterium peracerosum–strigosum–littorale (C. psl.) complex are unicellular charophycean algae in which there are two modes of zygospore formation, heterothallic and homothallic. A homothallic strain of Closterium (designation, kodama20) was isolated from a Japanese rice paddy field. Based on alignment of the 1506 group-I introns, which interrupt nuclear SSU rDNAs, homothallic kodama20 is most closely related to the heterothallic mating group II-B, which is partially sexually isolated from group II-A. Time-lapse photography of the conjugation process in kodama20 revealed that most of the observed zygospores originated from one vegetative cell. The sexual conjugation process consisted of five stages: (1) cell division resulting in the formation of two sister gametangial cells from one vegetative cell, (2) formation of a sexual pair between the two sister gametangial cells (or between gametangial cells of another adjoined individual), (3) formation of conjugation papillae, (4) release of gametic protoplasts from both members of a pair, and (5) formation of the zygospore by protoplast fusion. For conjugation to progress, the cell density and light condition in the culture was critical. We suggested the presence of a conjugation promotion factor.

A New Thermophilic Species of Conidiobolus from India

A Conidiobolus isolate growing optimally at 40 degrees C was isolated from decomposing leaf litter and has been designated as a new species, Conidiobolus thermophilus. Colony growth, conidial discharge and smooth zygospore formation was rapid at 40 degrees C, while comparative growth at 35 and 45 degrees C was slower. On the basis of its thermophilic character and morphological distinctness from all other species, the isolate is considered as a species new to science. There have been no published reports of any thermophilic or thermotolerant strains of Conidiobolus. The present fungus was isolated as part of an ongoing programme of selective isolation of unusual/rare thermophilic fungi from compost and decomposed terrestrial plant materials.

Revision of the genus Absidia ( Mucorales, Zygomycetes) based on physiological, phylogenetic, and morphological characters; thermotolerant Absidia spp. form a coherent group, Mycocladiaceae fam. nov.

The genus Absidia comprises ubiquitously distributed soil fungi inhabiting different growth temperature optima ranging from 20–42 °C. Some of the mesophilic species are important biotechnologically in the biotransformation of steroids or as producers of rennin-like components, whereas species with higher growth temperature optima are of clinical relevance as opportunistic human pathogens. The aim of this study was to investigate the phylogenetic relationships between these species and to establish a revision of their systematics. For this purpose single and combined genealogies based on distance, MP, ML, and Bayesian analyses of aligned nucleotide sequences of the nuclear-encoded genes for actin ( act) and for the 5.8S ribosomal RNA flanked by the ITS regions 1 and 2 (comprising 807 and 828 characters, respectively) of 16 Absidia species were reconstructed. The phylogenetic reconstructions suggest a trichotomy of the Absidia genus consisting of a mesophilic, a fast-growing thermotolerant, and a slowly-growing mycoparasitic Absidia group. The trichotomous phylogenetic grouping is concordant with the morphology of the zygospores, which are zygotes resulting from sexual conjugation between two compatible mating partners. Whereas the mesophilic group comprises the majority of absidiaceaeous species forming sterile hair-like, mycelial appendages on the suspensors of their zygospores, the thermotolerant group is characterised by the formation of smooth-walled zygospores, and the mycoparasitic group, namely Absidia parricida and A. zychae, by Mucor-like rough-walled zygospores. Based on the phylogenetic coherence of mesophilic and thermotolerant Absidia species, we propose that the two groups are separated into two distinct genera, Absidia for the mesophilic Absidia species resembling the Absidiaceae and Mycocladus for the thermotolerant species A. corymbifera, A. blakesleeana and A. hyalospora. Because Mycocladus is physiologically, phylogenetically, and morphologically distinct from the Absidiaceae s. str. we suggest that they are classified as a separate family, Mycocladiaceae fam. nov., which comprises the three species M. corymbifer, M. blakesleeanus and M. hyalospora.

Zygospore formation of four rare desmids from Kerala, India

AbstractZygospore formation of four rare taxa of desmids are described. The species include Cylindrocystis brebissonii var. minor West & G.S.West, Penium spinospermum Joshua, Actinotaenium obcuneatum (W.West) Teiling and A. inconspicuum (West & G.S.West) Teiling collected from different places of Wyanad District of Kerala, India. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)