Texte remanié de: Th. Doct.--Kassel--Universität des Landes Hessen, 1999. / Bibliogr. p. [174]-186. Index.

Salsola L. is one of the largest genera within the Chenopodiaceae. It has been suggested that almost 90 species occur in southern Africa where the plants are most conspicuous in karroid areas. Members of Salsola are of considerable importance as pasture plants in the Karoo, especially during winter and periods of prolonged drought. Some species also have medicinal and other valuable properties. However, not all Salsola species are beneficial; some may cause diseases and deficiencies in livestock, leading to high mortalities and severe financial loss. Because of the occurrence of harmful and beneficial species within the same area, correct identification of the different species is of extreme importance. Correct identification is, however, rendered problematic by the great morphological similarity of almost all southern African Salsola species and uncertainties concerning the infrageneric classification of the group. There is a great need for a system of easy identification that can be used in the herbarium as well as in the field. This is especially so since available keys to the group cannot be used to identify sterile specimens. There also exists great uncertainty as to the exact identity of most of the 69 new species described by V.P. Botschantzev (Komarov Botanical Institute, St Petersburg) between 1972 and 1983. For this reason many of the names have hardly been taken up and used by South African botanists. A clear delimitation of the different character states within the genus would greatly facilitate and enhance the process of solving the systematic problems that exist within the genus. A comparative anatomical study of the leaves of southern African Salsola species was conducted using LM and SEM techniques. Leaf anatomy proved to be very useful for delimiting groups within the genus. Of particular importance is the structure of the leaf in transverse section and the type of the indumentum. The investigated species can be primarily divided into two main leaf types, according to the presence or absence of a uniseriate hypodermis underlying the adaxial epidermis. A secondary division can be made by indumentum types. Four main indumentum types have been identified based on the appearance of the abaxial leaf surface. One of these indumentum types can be further subdivided according to the area of the leaf covered by trichomes and the number of elongated cells in the trichomes. There is a weak association between leaf type and subsection, as well as between leaf type and indumentum type. No obvious association could be found between leaf or indumentum type and fruit type or any other macromorphological character. Further investigation in this respect is required. In general the species possessing an adaxial hypodermis tend to have a denser covering of trichomes than those species lacking one. This denser indumentum probably provides the plants with better insulation to help prevent excessive water loss and to protect subtending tissues from extreme heat in their arid environment. When studied in combination with other anatomical and ecological evidence these characteristics might prove to be very useful to help establish a classification system whereby Salsola species can be more easily identified. / Dissertation (MSc (Botany))--University of Pretoria, 2000. / Plant Science / unrestricted

Salsola australis is an introduced weed of crop and pasture systems in the Western Australian broad acre cropping and pasture region (wheat-belt). This thesis investigated the classification, biology and ecology of the genus Salsola in southwest Australia, as well as modelling the effectiveness of possible weed control practices. Prior to this research, S. tragus was the only recognised species of the Salsola genus within Australia. However, genetic analysis revealed that four genetically distinct putative taxa of the genus Salsola were found in southwest Australia, none of which were S. tragus. The taxa that is the most prevalent agricultural weed was classified as S. australis, but the other three putative taxa could not be matched to recognised species. All four taxa were diploid (2n = 18), as opposed to tetraploid (2n = 36) S. tragus. Within the agricultural system of southwest Australia, S. australis plants established throughout the year, although the majority of seed production occurred in late summer and autumn. Total seed production (138-7734 seeds per plant) and seed viability (7.6-62.8%) of S. australis were lower than that reported for other agricultural weed species of the Salsola genus. Seed dispersal occurred when the senesced plants broke free of their root system to become mobile. Wind driven plants travelled and shed seed over distances of 1.6 to 1247.2 m. Movement of approximately half the plants was restricted to less than 100 m by entanglement with other S. australis plants within the stand. Some seed was retained on the senesced plants, but the germinability of this seed fell to less than 2% in the two month period following plant senescence (i.e. a decline of 79%). Once seed shed into the soil seed bank, anywhere from 32.3 to 80.7% of the viable seeds germinated in the year following seed production, with the rest remaining dormant or degrading. A model of the life cycle of S. australis based on the population ecology data indicated that the dormant seed bank had very little effect on annual seedling recruitment, but seed dispersal from neighbouring populations had a large impact on population growth rate. Therefore, the most successful weed control measures were those that restricted seed dispersal from neighbouring populations, or those that were applied to all populations in the region rather than to a single population. Weed control techniques applied to a single population, without reducing seed dispersal, could not reduce population size.

No description available.

Russian thistle (Salsola tragus L.) invaded areas of native montane grassland important to winter survival of bighorn sheep (Ovis canadensis Shaw) were studied in Jasper National Park, Alberta, Canada. The biology of Russian thistle and its control in the Park were studied in the field and greenhouse. Russian thistle in grasslands were 9.1 cm tall with 37.5 seeds per plant, whereas larger plants in naturally disturbed habitats were 29.8 cm tall with 1562.4 seeds per plant. Plants travelled up to 4,180 m during dispersal. With soil seed contact, litter depth did not inhibit performance or survivability; without soil contact, thick litter reduced germination and plant performance. Russian thistle responded positively to increased greenhouse temperature and drier conditions. Seven control treatments involving herbicide, seeding mixes, hand pulling, and grazing exclusion were assessed. Grazing exclusion was the best field management option, increasing litter and biomass, while reducing Russian thistle density and biomass. / Land Reclamation and Remediation