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Autecology and embryology of Audouinia capitata (Bruniaceae), a threatened species in the Cape floristic region
Dissertation (Ph. D.) -- University of Stellenbosch, 1992.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2012
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| _version_ | 1867614030108033024 |
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| access_status_str | Open Access |
| author | De Lange, Johannes Hendrik |
| author2 | Boucher, C. |
| author_browse | Boucher, C. De Lange, Johannes Hendrik |
| author_facet | Boucher, C. De Lange, Johannes Hendrik |
| author_sort | De Lange, Johannes Hendrik |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Dissertation (Ph. D.) -- University of Stellenbosch, 1992. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/69520 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:45:32.686Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2012 |
| publishDateRange | 2012 |
| publishDateSort | 2012 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/69520 Autecology and embryology of Audouinia capitata (Bruniaceae), a threatened species in the Cape floristic region De Lange, Johannes Hendrik Boucher, C. Van der Walt, J. J. A. Stellenbosch University. Faculty of Science. Dept. of Botany & Zoology. Bruniaceae -- Ecology Bruniaceae -- Embryology Dissertations -- Botany Dissertation (Ph. D.) -- University of Stellenbosch, 1992. 1. Audouinia capitata (L.f.) Brongn. is endemic to the Cape Floristic Region. The monotypic Audouinia is considered to be the most primitive genus in Bruniaceae and to be in a retrogressive state. It has been given a "Vulnerable" rating in the Red Data Book for plants in the Fynbos and Karoo Biomes. A total of 1200 plants are known to be distributed through 27 populations. Eighteen of the populations each have less than 14 plants and five localities each have solitary plants. Most of the populations are located on the southern slopes of mountains or rocky outcrops. The species is a long-lived (ca. 100 years) subshrub which resprouts after fire. 2. The majority of the ovaries are trilocular containing six ovules. The ovules are anatropous, unitegmic and crassinucellate. Embryo sac development conforms to the Polygonum type, and endosperm development is of the "nuclear" type. The dormant seed contains a rudimentary, heart-shaped embryo. The fruits are indehiscent. 3. Mass starch deposition is found in the mature embryo sac. Involvement of the persistent synergid, suspensor and endosperm in nutrition of the developing embryo is suggested. Lipids and proteins are the major storage compounds present in the starchless endosperm of the dormant seed. The seeds store nitrogen and phosphorus and also contain substantial concentrations of copper, zinc and manganese. Globoid inclusions of protein bodies in the seed are a major source of phosphorus, potassium, chlorine and magnesium and epidermal endosperm crystals, a major one for calcium. No crystalloids are found in the protein bodies. 4. The prevalance of non-viable pollen and insufficient insect-mediated transfer of pollen between the plants, which have an insignificant ability to produce seed following self-pollination, are limiting factors in reproduction. 5. The incidence of seed abortion is much higher than that implied by a fixed general system of one seed per 6-ovuled, indehiscent ovary. In many fertilized ovules the primary endosperm nuclei remain undivided, enlarge considerably and eventually degenerate. 6. The levels of seed set in the populations having less than approximately 10 plants each, are generally much lower than those in the large populations. 7. The germination of soil-stored seed was found to be initiated by exposure of the soil surface to smoke derived from burning fynbos plant material. High levels of germination can also be initiated by applying aqueous smoke extracts onto the soil. This indicates that a chemical stimulant is present in the smoke. 8. Summer (November - March) smoke treatments initiate a high germination response during the first winter (May - August). In contrast, smoke applied during mid-May elicites no response during the first winter and a poor response the following winter. A smoke application in mid-June elicites no response during either the first or the second winter. 9. On average 98 seeds were produced annually per plant. After a tire-free period of more than ten years, however, averages of only 4. 7 and 0.4 seedlings per plant were recruited following summer and winter bums respectively. A policy of late autumn and winter bums may be fatal for the survival of the species. 10. Plants respond favourably to fire at a post-fire age of 11 years. Some populations, however, are still vigorous and sexually productive at a post-tire age of 20 years. Fires at intervals as short as approximately four years will destroy major portions of the seed banks because the indehiscent fruits are not myrmecochorous and only become buried in the soil with time. Similarly, frequent tires will probably also kill many of the small, slow-growing seedlings. 11. The vegetative vigour of shoots, the size and number of inflorescences, and seed set, are increased by fire. 12. A high incidence of pre-emergent seedling mortality occurs. The low densities of protein bodies found in many of the seeds contribute to this mortality. Even when fruits were buried at an optimum soil depth and kept in a favourable moisture and temperature regime 39% of germinated seeds were not able to emerge from the soil. No evidence of widespread predation of seeds was observed. 13. On average, seedlings are located only 600 mm from the parent plant with the furthest seedling being recorded at a distance of 2.5 m. The absence of long-range dispersal mechanisms in this species limits its ability to extend its range through exploitation of scattered suitable micro-habitats. 14. The vast majority of seedling mortalities occur during summer and autumn. After five years the mortality rate of seedlings is 89 % - 95 % . Few seedlings were found to be damaged by herbivory. Three years after emergence their roots are mainly confined to the top 100 mm of soil. The average above-ground seedling height is only 55 mm after five years. 15. The generally shallow soils in which the species grows are leached, acid and nutritionally poor, particularly in nitrogen, phosphorus and total exchangeable cations. 16. The soil is sandy (97% m/m sand) and has a low water holding capacity (about 9% v/v). During most of the dry, hot and windy period (November - March), soil water tensions to a depth of t50 mm are much lower than 1 500 kPa. During the same period, daily maximum temperatures are high in the top 20 mm of soil, a depth which includes the major part of the seed bank. 17. Infestations of invasive exotic plants possibly contributed to the extinction of at least one population and has resulted in decreased numbers of plants in two other populations. They also pose a threat to four additional populations which contain 43 % of all known A. capirara individuals. 18. The xeromorphic leaves are a functional adaptation to survive in the harsh mediterranear climate. Mycorrhizas increase the absorption of nutrients from the nutrient-poor soils in which the species grows. 19. A factor in favour of the survival of the species is that 21 of the 27 known populations are located in nature reserves. 20. The species has horticultural potential and its cultivation offers a means to conserve it. Plants have been established successfully in the Kirstenbosch National Botanical Garden near Cape Town. 21. All plants in 26 of the natural populations were coded and mapped. This information is available for use in future demographic studies. 22. The unfavourable present climatic conditions and fire regime, poor pre-emergent reproductive success, low levels of recruitment and alien invasive vegetation represent major threats to the survival of this relict species. The extinction of at least five of the 27 populations within a single generation is inevitable. The survival of 12 additional populations over the next few generations is uncertain. Doctoral 2012-08-27T12:27:07Z 2012-08-27T12:27:07Z 1992 Thesis http://hdl.handle.net/10019.1/69520 en Stellenbosch University 291 pages : ill. application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Bruniaceae -- Ecology Bruniaceae -- Embryology Dissertations -- Botany De Lange, Johannes Hendrik Autecology and embryology of Audouinia capitata (Bruniaceae), a threatened species in the Cape floristic region |
| title | Autecology and embryology of Audouinia capitata (Bruniaceae), a threatened species in the Cape floristic region |
| title_full | Autecology and embryology of Audouinia capitata (Bruniaceae), a threatened species in the Cape floristic region |
| title_fullStr | Autecology and embryology of Audouinia capitata (Bruniaceae), a threatened species in the Cape floristic region |
| title_full_unstemmed | Autecology and embryology of Audouinia capitata (Bruniaceae), a threatened species in the Cape floristic region |
| title_short | Autecology and embryology of Audouinia capitata (Bruniaceae), a threatened species in the Cape floristic region |
| title_sort | autecology and embryology of audouinia capitata bruniaceae a threatened species in the cape floristic region |
| topic | Bruniaceae -- Ecology Bruniaceae -- Embryology Dissertations -- Botany |
| url | http://hdl.handle.net/10019.1/69520 |
| work_keys_str_mv | AT delangejohanneshendrik autecologyandembryologyofaudouiniacapitatabruniaceaeathreatenedspeciesinthecapefloristicregion |