Ascospore Morphology Research Articles

Molecular phylogenetics of Pleosporales: Melanommataceae and Lophiostomataceae re-circumscribed (Pleosporomycetidae, Dothideomycetes, Ascomycota)

The classification of Pleosporales has posed major challenges due to the lack of clear understanding of the importance of the morphological characters used to distinguish between different groups in the order. This has resulted in varied taxonomic treatments of many families in the group including Melanommataceae and Lophiostomataceae. In this study we employ two nuclear DNA gene markers, nuclear ribosomal large subunit DNA and translation elongation factor 1-alpha in order to examine the molecular phylogenetics of Pleosporales with strong emphasis on the families Melanommataceae and Lophiostomataceae. Phylogenetic analyses recovered Melanommataceae, Lophiostomataceae, Hypsostromataceae, and a few others as strongly supported clades within the Pleosporales. Melanommataceae as currently circumscribed was found to be polyphyletic. The genera Byssosphaeria, Melanomma, and Pseudotrichia were recovered within the family, while others such as Ostropella and Xenolophium nested outside in a weakly supported group along with Platystomum compressum and Pseudotrichia guatopoensis that may correspond to the family Platystomaceae. The genus Byssosphaeria was recovered as a strongly supported group within the Melanommataceae while Melanomma was weakly supported with unclear relationships among the species. The genera Herpotrichia and Bertiella were also found to belong in the Melanommataceae. Lophiostomataceae occurs as a strongly supported group but its concept is here expanded to include a new genus Misturatosphaeria that bears morphology traditionally not known to occur in the family. The strongly supported clade of Misturatosphaeria contains nine species that have gregarious, papillate ascomata with lighter coloured apices and plugged ostioles and that vary in ascospore morphology from 1- to 3-septate to muriform. Along with a strongly supported Lophiostoma clade, also within the family are Thyridaria macrostomoides based on new sequences from Kenyan collections and Massariosphaeria triseptata, M. grandispora, Westerdykella cylindrica and Preussia terricola based on GenBank sequences. The family Hypsostromataceae was recovered as a strongly supported monophyletic group nested within the Pleosporales.

Stem and Crown Rot of Chickpea in California Caused by Sclerotinia trifoliorum.

The identities of Sclerotinia isolates obtained from chickpea plants showing stem and crown rot were determined using morphological characteristics, variations in group I introns, and internal transcribed spacer (ITS) sequences. Isolates could be separated into two groups based on growth rates at 22°C, fast growing (about 40 mm per day) versus slow growing (about 20 mm per day). All fast-growing isolates induced stronger color change of a pH-indicating medium than did slow-growing isolates at 22°C. The slow-growing isolates contained at least one group I intron in the nuclear small subunit rDNA, whereas all fast-growing isolates lacked group I introns in the same DNA region. ITS sequences of the slow-growing isolates were identical to sequences of Sclerotinia trifoliorum. Those of the fast-growing isolates were identical to sequences of S. sclerotiorum. Finally, the slow-growing isolates showed ascospore dimorphism, a definitive character of S. trifoliorum, whereas the fast-growing isolates showed no ascospore dimorphism. Isolates of both species were pathogenic on chickpea and caused symptoms similar to those observed in the field. This study not only associated the differences between S. sclerotiorum and S. trifoliorum in growth rates, group I introns, ITS sequences, and ascospore morphology, but also represented the first report that S. trifoliorum causes stem and crown rot of chickpea in North America.

A new species of Camarops and phylogenetic analysis of related taxa in the Boliniaceae

Camarops rogersii is described as a new species in the family Boliniaceae (Order Boliniales) from Puerto Rico, distinguished by confluent, monostichous, soft, brightly-colored stromata. It is most similar to Camarops flava and Mollicamarops stellata . These taxa differ in ascospore morphologies, distant geographic distributions and their occurrence in distinct habitats. Camaropella pugillus is reassessed based on a collection from North Carolina and compared to Camaropella lutea . Phylogenetic analysis of nuclear 28S large subunit (LSU) DNA sequences supports the recognition of these taxa.

Phylogenetic placement and taxonomic review of the genus Cryptosporella and its synonyms Ophiovalsa and Winterella ( Gnomoniaceae, Diaporthales)

The type species of Cryptosporella, C. hypodermia, and Ophiovalsa, O. suffusa, as well as closely related species were studied using morphological, cultural, and DNA sequence characteristics. DNA sequence data from three different loci (ITS, LSU, and RPB2) suggest that C. hypodermia and O. suffusa are congeneric within the Gnomoniaceae ( Diaporthales). This result is supported by similarities in perithecial, ascal and ascospore morphology, and lifestyles characterized as initially endophytic, becoming saprobic as plant tissues die. Furthermore, both type species produce Disculina anamorphs. A review of the literature indicates that the generic name Cryptosporella has priority over Ophiovalsa and its synonym Winterella sensu Reid & Booth (1987). A redescription of the genus Cryptosporella is included, as well as a description of C. hypodermia, C. suffusa, the type species of Ophiovalsa, a brief account of the other seven species accepted in Cryptosporella, and a key to species of Cryptosporella. Eight new combinations are established: C. alnicola (Fr.) L.C. Mejía & Castleb., comb. nov.; C. betulae (Tul. & C. Tul.) L.C. Mejía & Castleb., comb. nov.; C. confusa (Reid & Booth) L.C. Mejía & Castleb., comb. nov.; C. corylina (Tul. & C. Tul.) L.C. Mejía & Castleb., comb. nov.; C. femoralis (Peck) L.C. Mejía & Castleb., comb. nov.; C. suffusa (Fr.) L.C. Mejía & Castleb., comb. nov.; C. tiliae (Tul. & C. Tul.) L.C. Mejía & Castleb., comb. nov.; and C. wehmeyeriana (Reid & Booth) L.C. Mejía & Castleb., comb. nov.

The polyphyletic nature of Pleosporales: an example from Massariosphaeria based on rDNA and RBP2 gene phylogenies

Massariosphaeria is a loculoascomycetous fungus currently accommodated within the Pleosporales. However, based on morphology alone, it has been difficult to assess its familial position and its affinities to other fungi with bitunicate asci. In order to establish its evolutionary relationships, two regions of the rDNA (18S and 28S) and two regions of the RPB2 protein-coding gene were sequenced and analysed phylogenetically. Multigene phylogenies revealed that Massariosphaeria is not monophyletic and results are in disagreement with existing morphological-based classification schemes. Characters, such as ascomatal shape and ascospore morphology, have evolved more than once within the Pleosporales. The familial placement of several species is still obscure, except M. grandispora, which could be confidently assigned to the Lophiostomaceae. M. typhicola is closely related to Trematosphaeria hydrela ( Melanommataceae), whereas M. triseptata is related to Melanomma radicans but shares close affinities to the Sporormiaceae. The placement of M. roumeguerei is still unresolved, and it does not appear to have any close evolutionary relationship to any known melanommataceous or pleosporaceous genera. Our molecular data also refute the monophyly of Kirschsteiniothelia, Massarina, Melanomma, and Pleospora, and support previous phylogenetic hypotheses that Melanommataceae is polyphyletic. There is a need for more phylogenetic (and taxonomic) studies within the Pleosporales, especially incorporation of more anamorphic taxa and type species.

Megalohypha, a new genus in the Jahnulales from aquatic habitats in the tropics

A new fungus collected from submerged wood in tropical forest streams in Panama and Thailand is described as a new genus and species in the Jahnulales. This fungus, Megalohypha aqua-dulces, is described based on ascospore morphology, which differs substantially from that of the other genera in the Jahnulales. It has these morphological features: ascomata hyaline, translucent, with subtending, wide, brown, septate, stoloniferous hyphae; peridium of large, thin-walled cells; hamathecium of septate pseudoparaphyses; asci clavate, fissitunicate, 8-spored; and ascospores 1-septate, brown, rough-walled, with longitudinal sulcate striations. An interesting feature of Megalohypha aqua-dulces, which it shares with some other taxa in Jahnulales, is the presence of both sessile and stalked fruiting bodies. In addition, the stalks have morphology that consists of a wide hypha with a narrower hypha apparently enclosed within and the stalks are strongly constricted at the septa.

Megalohypha, a new genus in the Jahnulales from aquatic habitats in the tropics

A new fungus collected from submerged wood in tropical forest streams in Panama and Thailand is described as a new genus and species in the Jahnulales. This fungus, Megalohypha aqua-dulces, is described based on ascospore morphology, which differs substantially from that of the other genera in the Jahnulales. It has these morphological features: ascomata hyaline, translucent, with subtending, wide, brown, septate, stoloniferous hyphae; peridium of large, thin-walled cells; hamathecium of septate pseudoparaphyses; asci clavate, fissitunicate, 8-spored; and ascospores 1-septate, brown, rough-walled, with longitudinal sulcate striations. An interesting feature of Megalohypha aqua-dulces, which it shares with some other taxa in Jahnulales, is the presence of both sessile and stalked fruiting bodies. In addition, the stalks have morphology that consists of a wide hypha with a narrower hypha apparently enclosed within and the stalks are strongly constricted at the septa.

Whatever happened to the pyrenomycetes and loculoascomycetes?

An overview of current phylogenetic studies employing molecular data to test previously formulated hypotheses of relationships of loculoascomycetes and pyrenomycetes is given, concentrating on three topics: (1) circumscription and classification of loculoascomycetes, (2) a new classification of Sordariales, and (3) the phylogenetic occurrence of lichenized pyrenomycetes. With regard to these three examples, our review indicates: (1) In traditional taxonomy ascomycetes were classified according to their ascoma-types, with the class Pyrenomycetes including all taxa having perithecia. Later, the development of ascomata and the type of ascus were employed for higher-level classification, and consequently, Loculoascomycetes was separated from Pyrenomycetes. However, molecular studies show that even these revised classifications were too coarse. The Loculoascomycetes fall into two distinct and not closely related groups, which are placed in two clades: Chaetothyriomycetidae and Dothideomycetes. (2) Ascospore morphology has been widely used in taxonomy of ascomycetes, and Sordariales is a prominent example of this. Molecular data suggest that ascomatal wall morphology is a better predictor of phylogenetic relationships in these fungi. Further, the molecular data helped to redefine the circumscription of Sordariales. (3) The majority of non-lichenized pyrenomycetes form a monophyletic group: Sordariomycetes. However, the lichenized pyrenomycetes are highly polyphyletic. Pyrenocarpous lichen-forming fungi occur in several lineages each in Dothideomycetes, Chaetothyriomycetidae, and Lecanoromycetes, whereas no lichenized forms are currently known in the classical pyrenomycetous Sordariomycetes.

The arachiform vacuolar body: an overlooked shared character in the ascospores of a large monophyletic group within Parmeliaceae ( Xanthoparmelia clade, Lecanorales)

Sections of apothecia were used to study the internal morphology of ascospores in the largest monophyletic clade within Parmeliaceae composed of Xanthoparmelia and related genera. The results were compared with fertile representative species of most other parmelioid clades. All the Xanthoparmelia species had spores with a single smooth vacuole, which was peanut-shaped, with different degrees of constriction in the equatorial plane. This differs from the ellipsoid vacuole of other parmelioids. In the Xanthoparmelia clade, sexual reproduction seems much more common than in other parmelioids. Thus, we suggest that the presence of this unique spore morphology might contribute to the evolutionary success of this monophyletic group. Further, the discovery of this useful ascospore character demonstrates that detailed ascospore morphological studies significantly enhance molecular phylogenetic analyses. Ascospore features may be more taxonomically significant in Parmeliaceae than hitherto considered.

Failure ofPhyllosticta citricarpapycnidiospores to infect Eureka lemon leaf litter

Pycnidiospores of Phyllosticta citricarpa from pure cultures, symptomatic citrus black spot Valencia orange fruit and peelings were evaluated for their potential to infect and colonise citrus black spot-free Eureka lemon leaf litter in a controlled environment and in the field in different production regions of South Africa. Leaf litter, consisting of freshly detached green and old brown leaves that were exposed to viable pycnidiospores under controlled conditions or in the field underneath citrus trees, were not infected and colonised by P. citricarpa. Ascospores, conforming to Guignardia citricarpa, the pathogen, or G. mangiferae, a cosmopolitan endophyte, were collected with a Kotze Inoculum Monitor from leaves placed in the field only at Tzaneen and Burgersfort. Distinguishing between these two species on ascospore morphology alone is not possible. A diagnostic polymerase chain reaction conducted on representative leaf material from all the treatments revealed the presence of only G. mangiferae on 12.5% of the treatments. This study demonstrated the failure of P. citricarpa pycnidiospores to infect citrus leaf litter under controlled and field conditions. Symptomatic citrus black spot fruit or peel lying on the ground underneath citrus trees, therefore, cannot lead to infection and colonisation of freshly detached leaves or natural leaf litter or represent a source of inoculum in citrus orchards for these leaves.

Phylogenetic classification of Cordyceps and the clavicipitaceous fungi

Cordyceps, comprising over 400 species, was historically classified in the Clavicipitaceae, based on cylindrical asci, thickened ascus apices and filiform ascospores, which often disarticulate into part-spores. Cordyceps was characterized by the production of well-developed often stipitate stromata and an ecology as a pathogen of arthropods and Elaphomyces with infrageneric classifications emphasizing arrangement of perithecia, ascospore morphology and host affiliation. To refine the classification of Cordyceps and the Clavicipitaceae, the phylogenetic relationships of 162 taxa were estimated based on analyses consisting of five to seven loci, including the nuclear ribosomal small and large subunits (nrSSU and nrLSU), the elongation factor 1α (tef1), the largest and the second largest subunits of RNA polymerase II (rpb1 and rpb2), β-tubulin (tub), and mitochondrial ATP6 (atp6). Our results strongly support the existence of three clavicipitaceous clades and reject the monophyly of both Cordyceps and Clavicipitaceae. Most diagnostic characters used in current classifications of Cordyceps (e.g., arrangement of perithecia, ascospore fragmentation, etc.) were not supported as being phylogenetically informative; the characters that were most consistent with the phylogeny were texture, pigmentation and morphology of stromata. Therefore, we revise the taxonomy of Cordyceps and the Clavicipitaceae to be consistent with the multi-gene phylogeny. The family Cordycipitaceae is validated based on the type of Cordyceps, C. militaris, and includes most Cordyceps species that possess brightly coloured, fleshy stromata. The new family Ophiocordycipitaceae is proposed based on Ophiocordyceps Petch, which we emend. The majority of species in this family produce darkly pigmented, tough to pliant stromata that often possess aperithecial apices. The new genus Elaphocordyceps is proposed for a subclade of the Ophiocordycipitaceae, which includes all species of Cordyceps that parasitize the fungal genus Elaphomyces and some closely related species that parasitize arthropods. The family Clavicipitaceae s. s. is emended and includes the core clade of grass symbionts (e.g., Balansia, Claviceps, Epichloë, etc.), and the entomopathogenic genus Hypocrella and relatives. In addition, the new genus Metacordyceps is proposed for Cordyceps species that are closely related to the grass symbionts in the Clavicipitaceae s. s. Metacordyceps includes teleomorphs linked to Metarhizium and other closely related anamorphs. Two new species are described, and lists of accepted names for species in Cordyceps, Elaphocordyceps, Metacordyceps and Ophiocordyceps are provided.

The family Pleosporaceae: intergeneric relationships and phylogenetic perspectives based on sequence analyses of partial 28S rDNA

The Pleosporaceae is an important loculoascomycete family. There has been disagreement, however, regarding the taxonomic placement of many genera within this family. This study investigates phylogenetic relationships among the genera Cochliobolus, Kirschsteiniothelia, Leptosphaerulina, Macroventuria, Pleospora, Pyrenophora, and Wettsteinina. Partial 28S rDNA sequences from taxa within these genera were analyzed with maximum parsimony, likelihood and Bayesian methods. Cochliobolus can be segregated broadly into two groups as previously proposed. Pleospora is polyphyletic in its current sense. Taxa with Stemphylium anamorphs are closely related to Cochliobolus and fit within the Pleosporaceae, whereas the affinities of Pleospora herbarum and P. ambigua are still ambiguous. Pyrenophora constitutes a monophyletic group within the Pleosporaceae, whereas Leptosphaerulina and Macroventuria appear to share phylogenetic affinities with the Leptosphaeriaceae and Phaeosphaeriaceae. Phylogenies indicate that Wettsteinina should be excluded from the Pleosporaceae. Similar findings are reported for Kirschsteiniothelia, which is probably polyphyletic. Anamorphic characters appear to be significant (especially in Cochliobolus) while ascospore morphologies, such as shape and color and substrate occurrence are poor indicators of phylogenetic relationships among these loculoascomycetes.

The family Pleosporaceae: intergeneric relationships and phylogenetic perspectives based on sequence analyses of partial 28S rDNA

The Pleosporaceae is an important loculoascomycete family. There has been disagreement, however, regarding the taxonomic placement of many genera within this family. This study investigates phylogenetic relationships among the genera Cochliobolus, Kirschsteiniothelia, Leptosphaerulina, Macroventuria, Pleospora, Pyrenophora, and Wettsteinina. Partial 28S rDNA sequences from taxa within these genera were analyzed with maximum parsimony, likelihood and Bayesian methods. Cochliobolus can be segregated broadly into two groups as previously proposed. Pleospora is polyphyletic in its current sense. Taxa with Stemphylium anamorphs are closely related to Cochliobolus and fit within the Pleosporaceae, whereas the affinities of Pleospora herbarum and P. ambigua are still ambiguous. Pyrenophora constitutes a monophyletic group within the Pleosporaceae, whereas Leptosphaerulina and Macroventuria appear to share phylogenetic affinities with the Leptosphaeriaceae and Phaeosphaeriaceae. Phylogenies indicate that Wettsteinina should be excluded from the Pleosporaceae. Similar findings are reported for Kirschsteiniothelia, which is probably polyphyletic. Anamorphic characters appear to be significant (especially in Cochliobolus) while ascospore morphologies, such as shape and color and substrate occurrence are poor indicators of phylogenetic relationships among these loculoascomycetes.

Novel Neosartorya species isolated from soil in Korea

Phenotypic and genotypic characters of strains of Neosartorya spinosa and related taxa were analysed. N. spinosa, Neosartorya botucatensis and Neosartorya paulistensis had identical partial beta-tubulin and calmodulin gene sequences and could not be differentiated on macro- and micro-morphological characteristics, including by scanning electron microscopy. Based on partial beta-tubulin and calmodulin gene sequences and ascospore morphology, two separate groups are distinguished and are proposed as novel species. Neosartorya laciniosa sp. nov. has microtuberculate ascospores with two bent crests and two distinct equatorial rings of small projections. Neosartorya coreana sp. nov. has rugose to weak reticulate ascospores with two often bent crests, but without the equatorial rings of small projections. The type strain of N. laciniosa is CBS 117721T (=NRRL 35589T=KACC 41657T) and the type strain of N. coreana is CBS 117059T (=NRRL 35590T=KACC 41659T).

Molecular systematics of Ceratostomella sensu lato and morphologically similar fungi

The systematic position and phylogenetic relationships of Ceratostomella sensu lato and phenotypically similar fungi using comparative morphological and culture studies and phylogenetic analyses of the nuclear large- and small-subunit ribosomal DNA were explored. In the light of inferred phylogenies and morphological data the genus Ceratostomella is redescribed, the generic concept is emended and four species are accepted (viz. C. cuspidata, C. pyrenaica, C. rhynchophora and C. rostrata). A new genus Xylomelasma is introduced and delimited from Ceratostomella, with two new species described (viz. X. novaezelandiae and X. sordida). In culture species of both Ceratostomella and Xylomelasma produced sterile mycelium. The genus Lentomitella with a phaeoisaria-like anamorph formed in vitro is reinstated to encompass taxa formerly attributed to the broadly perceived Ceratostomella with three accepted species (viz. L. cirrhosa, L. crinigera and L. tomentosa). Lentomitella and Ceratostomella are clearly distinguishable by the morphology of asci, ascospores and centrum. Lentomitella is compared to phenotypically similar Ceratosphaeria, which formed a harpophora-like anamorph in vitro. In the present phylogenies Ceratostomella, Ceratosphaeria, Lentomitella and Xylomelasma are shown as clearly separate genera belonging to three different groups of perithecial ascomycetes. Ceratostomella, Lentomitella and Xylomelasma reside within a large unsupported clade consisting of members the Ophiostomatales, the freshwater Annulatascaceae and a group of nonstromatic, terrestrial taxa. Ceratosphaeria is well supported within the Magnaporthaceae. The systematic value of morphological characters of ascospores, paraphyses, asci, centrum and conidiogenesis in segregating taxa from Ceratostomella sensu lato and their relatives is discussed.

Morphological studies in Rosellinia (Xylariaceae): the first step towards a polyphasic taxonomy

More than 90 species are accepted in the xylariaceous genus Rosellinia. Thorough morphological characterisation of all known species will provide a taxonomic hypothesis that can be later tested by DNA sequence analysis. Exploratory analyses of ascospore morphology, shape of ascus apical structure, and anamorph genus suggest six morphological groups in the genus.

Multi-gene phylogenies indicate ascomal wall morphology is a better predictor of phylogenetic relationships than ascospore morphology in the Sordariales (Ascomycota, Fungi)

Ascospore characters have commonly been used for distinguishing ascomycete taxa, while ascomal wall characters have received little attention. Although taxa in the Sordariales possess a wide range of variation in their ascomal walls and ascospores, genera have traditionally been delimited based on differences in their ascospore morphology. Phylogenetic relationships of multiple representatives from each of several genera representing the range in ascomal wall and ascospore morphologies in the Sordariales were estimated using partial nuclear DNA sequences from the 28S ribosomal large subunit (LSU), β-tubulin, and ribosomal polymerase II subunit 2 (RPB2) genes. These genes also were compared for their utility in predicting phylogenetic relationships in this group of fungi. Maximum parsimony and Bayesian analyses conducted on separate and combined data sets indicate that ascospore morphology is extremely homoplastic and not useful for delimiting genera. Genera represented by more than one species were paraphyletic or polyphyletic in nearly all analyses; 17 species of Cercophora segregated into at least nine different clades, while six species of Podospora occurred in five clades in the LSU tree. However, taxa with similar ascomal wall morphologies clustered in five well-supported clades suggesting that ascomal wall morphology is a better indicator of generic relationships in certain clades in the Sordariales. The RPB2 gene possessed over twice the number of parsimony-informative characters than either the LSU or β-tubulin gene and consequently, provided the most support for the greatest number of clades.

Towards a phylogenetic classification of Cordyceps: ITS nrDNA sequence data confirm divergent lineages and paraphyly

The ascomycetous genus Cordyceps accommodates endoparasitic species that attack arthropods or other fungi. Analyses of ITS nrDNA sequence data of 72 taxa from the teleomorph genera Cordyceps, Claviceps, Epichloë, and the anamorph genera Akanthomyces, Beauveria, Metarhizium, Hirsutella, Hymenostilbe, Paecilomyces, Polycephalomyces, and Tolypocladium assigned the taxa to four main evolutionary lineages not reflected in the current classification of Cordyceps. Ten subclades were recognized from separate analyses of data subsets. Judged from the ITS phylogenies, Cordyceps spp. with branched stromata were highly supported as a divergent lineage. Host specificity was found to be of limited phylogenetic significance, and several host shifts are suggested to have occurred during the evolution of Cordyceps. Similar ascospore morphology was not reflected in the phyletic groups, and closely related taxa showed large interspecific variation with respect to the number of segments in which the ascospores are divided. However, combinations of selected characters were found to delimitate some lineages, e.g. all Cordyceps spp. that attack hosts in the insect orders Coleoptera and Lepidoptera, and with non-immersed perithecia and clavate to acicular, brightly yellowish to reddish stromata, constituted a separate clade. Furthermore, all Cordyceps spp. with perithecia obliquely immersed in the stroma were recognized as a distinct monophyletic group. This clade is additionally characterized by the formation of anamorphs ascribable to the genus Hymenostilbe. The mycogenous Cordyceps spp. grouped in a separate subclade, interspersed by two cicadaen parasites and all Tolypocladium spp. except T. parasiticum. Tolypocladium and Beauveria were found to be polyphyletic. The included Claviceps and Epichloë taxa appeared to be derived within Cordyceps, thus making Cordyceps paraphyletic as suggested in other studies.

Cordyceps cardinalis sp. nov., a new species of Cordyceps with an east Asian-eastern North American distribution

Cordyceps cardinalis, a pathogen of lepidopteran larva, is described as a new species from the southern Appalachian Mountains of the eastern United States and from southeastern Japan. It is macroscopically similar to both C. militaris and C. pseudomilitaris, however, microscopic, cultural and molecular evidence support it being a phylogenetically distinct species. Cordyceps cardinalis is most similar to C. pseudomilitaris in the microscopic characters of non-disarticulating ascospore morphology and its host affinity for lepidopteran larvae, which contrast with the characters of C. militaris. Aspects of morphology, host association, phylogeny and biogeography are discussed.

Variation in functional ascospore parts in the ascomycetous yeast Dipodascopsis uninucleata.

A variation in functional ascospore morphology was detected using electron microscopy (EM) in two varieties of the yeast Dipodascopsis uninucleata, i.e., D. uninucleata var. uninucleata and D. uninucleata var. wickerhamii. It was found that the latter produces ascospores characterized by the absence of small surface hooks which have been implicated in the release and re-assembly of ascospores in D. uninucleata var. uninucleata. These varieties are closely related on the basis of their mode of sexual reproduction, ascospore morphology as observed under the light microscope, physiological characteristics as well as the extent of divergence in the variable D1/D2 domain of the large subunit 26S ribosomal DNA.