Genus

About: Genus is a research topic. Over the lifetime, 68921 publications have been published within this topic receiving 590966 citations. The topic is also known as: monospecies genus & genus (zoology).

Distribution of Pollen Types in Vernonia (Vernonieae: Compositae)

Abstract: Vernonia is the largest genus of the tribe Vernonieae with nearly 1000 species found predominately in the New and Old World tropics. Morphological variation in vegetative features is extensive; however, floral characters are relatively uniform. This uniformity has led to difficulties in understanding relationships within Vernonia. Pollen morphology is distinctive however, and of taxonomic value in as- sessing infrageneric groups. In an attempt to understand better the patterns of radiation in the genus, pollen from over 500 species of Vernonia was examined from throughout the geographical range by light microscopy and SEM. There are six basic types of pollen grains. The distribution of pollen types is correlated with the radiation of related species groups. A widespread, probably ancestral, pollen type is found in both the New and Old Worlds, but other types are found to be exclusive to, or to predominate in, one hemisphere. Structural changes appear to be associated with functional modifications. The pattern of pollen distribution appears to reflect the evolutionary divergence of species within the genus over time and supports a broad concept of the genus.

Importance of Leaf Epidermal Characters in the Asteraceae Family

Abstract: A comparative study of the leaf epidermis of twelve species in the Compositae (Asteraceae) family was undertaken in order to document characters that are important in the taxonomy of the family. It was observed that trichomes can be successfully used for the delimitation of genera within the family. Within each species however, there are varied assortment of trichomes with occasional transitions among them. Launaea taraxacifolia was unique in being the only species without any trichome. Stellate trichome type and K-shaped or tetraradiate trichomes were observed in Tridax procumbens only. The genus Vernonia can be delimited from the other genera by the possession of T - shaped trichomes which are absent in the other genera, while amoeboid-shaped trichomes can be found in the genus Chromolaena only. Within the same genus, the species can also be delimited on the basis of possession of unique trichome types, for example in the genera Vernonia and Emilia. Cuticular striations occur in only two species out of the twelve studied, on the abaxial surface of V. amygdalina and on both surfaces of Bidens pilosa. Four stomatal types were recorded for the family, anomocytic, brachyparacytic, anisocytic and diacytic. Stomatal type was observed to delimit not only at generic level, but also at specific or species level. Ageratum conyzoides and Synedrella nodiflora are the only two species with occasional diacytic stomatal types. Results of the statistical correlation analysis for stomatal size and stomatal index at the 0.05 and 0.01 levels revealed high positive correlation for species in the same tribe, as well as for species in different tribes affirming close interrelationship and overlap of the values of stomatal indices and sizes within the family. Foliar anatomical characters that justify the separation of Vernonia amygdalina and Vernonia cinerea into separate tribes are highlighted.

Pacispora, a new vesicular arbuscular mycorrhizal fungal genus in the Glomeromycetes

Abstract: A new genus in the fungal family Glomeraceae, order Glomerales of the Glomeromycetes class is described, named Pacispora. The type species is P. scintillans which, as P. dominikii and P. chimonobambusae, was formerly placed in the genus Glomus of the Glomeraceae. Two of the already known species are re-described in this paper, and four new species of the new genus are published herein: Pacispora franciscana, P. robigina, P coralloidea and P boliviana. Spores of the new genus are formed terminally on hyphae, a feature they share only with Glomus and Paraglomus. An inner, usually three-layered wall is present inside the spores, from which the spores germinate directly through the outer spore wall, which usually is also three-layered. This germination characteristic is shared with Scutellospora, Acaulospora and Entrophospora but not with Glomus and Paraglomus. The formation of vesicular arbuscular mycorrhiza - so far confirmed for two of the seven Pacispora spp. -, the staining characteristics of the root internal fungal structures and the features of the subtending hyphae of the spores are most similar to species of the genus Glomus. For these reasons, we currently suggest to include Pacispora into the Glomeraceae. The seven Pacispora spp. can morphologically be differentiated by the spore surface structure, the characteristics of the spore wall ornamentation, and by the spore color and spore size. An identification key is presented. Three of the Pacispora spp. were abundantly detected in the high altitudes of the Swiss Alps. However, the occurrence of this genus in temperate, mediterranean and tropical regions suggests that Pacispora is ubiquitous and adapted to many terrestrial environments.

The Australian Portunids (Crustacea : Portunidae). III. The Genus Portunus

Abstract: Thirteen species of the genus Portunus Weber are recorded from Australia, including one new species and five new records. These species are described and illustrated, and a key is given to Bnown Indo-West-Pacific species. First pleopods of males are considered in detail and a key based on their features is included. The problems of designating subgenera are discussed and the relevance of a knowledge of the structure of first male pleopods is indicated.

Phylogeographic analysis of the threatened and endangered superconglutinate‐producing mussels of the genus Lampsilis (Bivalvia: Unionidae)

Abstract: Several species of freshwater unionid mussels in the genus Lampsilis exhibit a remarkable reproductive strategy. Female mussels of these species enclose their larvae in a minnow-like lure, called a ‘superconglutinate’, to attract piscivorous fishes. When a fish attempts to ingest the superconglutinate the lure ruptures and the larvae are released to parasitize the fish. Of the four species of mussel which exhibit this strategy and are endemic to the Gulf Coast drainages of the southeastern United States, three are protected under the Endangered Species Act, and one is recognized as imperilled. Phylogenetic analysis of nucleotide sequences of the mitochondrial 16S ribosomal RNA and the first subunit of the cytochrome oxidase c genes was conducted on 18 individual specimens representing these four species and six outgroup taxa. Phylogenetic analyses of these data support the monophyly of the superconglutinate-producing mussels, and indicates a strong geographical component to the data. The zoogeographic patterns of the four taxa included in the study are congruent with those seen in freshwater vertebrates, and are consistent with a vicariant pattern resulting from fluctuations in sea level during the Pleistocene. Despite the strong geographical structuring of the data, only one species, Lampsilis subangulata , was recovered as monophyletic. The authors attribute the lack of support for the monophyly of the remaining species to insufficient sequence variation and the recent origin of the ancestor of these taxa. Based on these data, any future captive breeding projects aimed at augmenting or re-establishing populations should do so only from the appropriate source populations so as to maintain the genetic integrity of these nascent species.