Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
Results
Showing 1 to 16 of 16 for “"Cycads"”.
-
Systematics and evolutionary biology of the Weevils associated with cycads in Australia
Cycads are subtropical and tropical palm-like gymnosperms, commonly known as "living fossils" as they arose in the late Paleozoic and were much more diverse and dominant during the Mesozoic. Modern cycads underwent a recent global diversification in Miocene (ca. 11-20 mya). Even though cycads were …
-
Systematics and evolutionary biology of the Weevils associated with cycads in Australia
Cycads are subtropical and tropical palm-like gymnosperms, commonly known as "living fossils" as they arose in the late Paleozoic and were much more diverse and dominant during the Mesozoic. Modern cycads underwent a recent global diversification in Miocene (ca. 11-20 mya). Even though cycads were …
-
In vitro tissue culture: Towards conservation of threatened desiccation sensitive Encephalartos cycads seeds
… species; however, the recalcitrant nature of cycads seeds makes it difficult to conserve using conventional seed banking methods. Recalcitrant seeds have a short lifespan and cannot be dried or stored for prolonged periods as they become non-viable when they lose moisture. While studies on …
-
Assessing species richness patterns and conservation threats (due to overharvesting and climate change) in South African Cycads, with emphasis on a population of Encephalartos tranvenosus Stapf and Burt Davy from the Soutpansberg Mountain, Limpopo Province
Cycads are regarded as the oldest living seed plants on earth and they have existed for about 300 million years. Ever since the awareness of the existence of this plant group, they have been facing high extinction risk. Currently they are referred to as the most threatened plant group in the world. …
-
The role of cone volatiles and thermogenesis in the pollination of Encephalartos cycads with particular reference to E.villosus
Pollination systems of cycads usually involve obligate mutualisms in which the cycad taxa depend on between one and three insect pollinators. Generally, the pollination periods of many cycad taxa are characterised by odour emissions in pollen shedding (male) and receptive (female) cones usually …
-
Cycad forensics: tracing the origin of poached cycads using stable isotapes, trace element concentrations and radiocarbon dating techniques
… from the upper, middle and lower sections of the cycads, which were cut into sections so that the inner, middle and outer rings for each core could be sampled. These samples were reduced to cellulose for δ18O and δ13C isotope analysis. Leaf bases were sampled from the upper, middle and lower …
-
Poaching of encephalartos transvenosus, in the Limpopo Province, South Africa
… and mapping the distribution of the poached cycads. For these specific objectives, field observation and open-ended questionnaire were used to collect the data. Field observations and questionnaires were conducted to investigate which part of the cycad is poached, Open-ended questions were …
-
Species-level phylogenetic reconstruction of the African cycad genus Encephalartos (Zamiaceae)
… which is one of the eleven genera of cycads. The genus is confined to Africa and comprises approximately 65 species, 38 of which are found naturally in South Africa. The phylogenetic studies on Encephalartos to date still result in many unresolved polytomies so it is not possible to …
-
Adaptation to the host-plant, and the evolution of host specialization, in 'cycad weevils' (Coleoptera: Brentidae)
… and appear to retain an ancient association with cycads, a group of plants that were widespread in the Mesozoic era (ca. 200 MYA) before the rise of the angiosperms and which are now represented by 11 genera with relict distributions in the tropics and sub-tropics. The primary aim of this research …
-
Studies in molecular structure of plant polysaccharides : exudates from Encephalartos species
… taxonomy is of particular interest where the cycads are concerned as these plants originated during the Mesozoic era and can therefore be considered as "living fossils". The exudate gums from six different species of the genus Encephalartos were surveyed, and the detailed molecular structures …
-
Molecular evolution of the RNA polymerase genes and the phylogeny of seed plants
… and four gymnosperms groups: conifers, cycads, Ginkgo and Gnetales). These organisms diverged roughly three hundred million years ago and evolved independently since then. Therefore, morphological characters have limited power in resolving their phylogeny. With the advancement of …
-
The lower cretaceous flora of the gates formation from western Canada
… and Elatides of Taxodiaceae, Elatocladus), cycads (Chilinia, Ctenis, Pseudocycas and Pterophyllum and two new genera), Gingko and Ginkgoites; leptostrobans (a new genus), Taeniopteris and unidentified angiosperms. In total, 52 species from 28 genera are described, including 5 new genera, 15 …
-
Crime, culture and collecting: the illicit cycad market in South Africa
… in South Africa, that of rare cycad plants. Cycads are widely exploited, moved and sold in the country by a network of increasingly criminalised operations. State action against these markets is not a priority and has had only few successes in limiting the trade of an increasingly scarce …
-
The ecology and management of the Kaapsehoop cycad (Encephalartos laevifolius Stapf and Burtt Davy)
… a background to the botanical significance of cycads in general, the reasons for the endangered status of E. laevifolius and a list of aims and objectives. The latter are briefly; to develop. an understanding of the ecology of this cycad, determine the nature and extent of the threats which …
-
Life history traits of South African Encephalartos spp. (Zamiaceae) and their implications for understanding population structure, responses to threats and effective conservation action
… analysis of life history traits was applied to cycads, the oldest living seeds plants which are at risk of extinction due to vulnerability to illegal wild harvesting and habitat loss. The study focused on South African cycad species within the genus Encephalartos, as well as two species from …
-
Effects of habitat degradation on the evolutionary dynamics of populations in a rainforest cycad (Gymnospermae)
In addition to habitat loss and fragmentation, habitat degradation can have important consequences for biodiversity and population persistence, including effects on ecological and genetic processes beyond decreased demographic viability and the loss of genetic variation. Particularly interesting is …