Thesis (Ph.D.) - Cairo University - Faculty of Science - Department of Botany and Microbiology

Ludwigia L. is a pantropic genus of aquatic or subaquatic herbs, represented in the Egyptian flora by L. stolonifera and L. erecta. L. stolonifera becomes one of the dominant aquatic macrophyte and expands its ecological range from fresh water to marine habitats and salt affected wetlands, while L. erecta is very rare. Samples of thirty two populations of L. stolonifera were studied and morphologically grouped into seven morphotypes based on macro and micro morphological characters. Notable floral characters were noticed as the presence of female and hermaphrodite flowers. By using SEM, the pollen grains appeared spheroidal, tricolporate with rugulate exine sculpturing. Variability in pollen grains among the seven morphotypes is detected. Cluster analysis and Jaccard's measure were elaborated to investigate similarity between each pair of the seven morphotypes. The floristic composition of the seven morphotypes revealed the presence of 60 associated species but their distribution is diversified. The effect of water-soil variables were studied using CCA and ANOVA. The electric conductivity, salinity, organic matter, sulphates and chlorides are the most significant variables. The plant exhibits morphological plasticity that further complicates its identification. The morphotypes of L. stolonifera will then be distinguished by karyotype and RAPD-PCR based markers. The basic chromosome number is eight (x=8). Tetraploid (2n= 32) and triploid (2n= 24) were detected during this study. The detection of triploidy and the satellite chromosome is the first time to be recorded in this species. Tetraploid morphotypes attain higher seed productivity than triploids. The chromosomes were highly variable in their length and centromere position. The dendrogram generated using RAPD markers revealed that the studied morphotypes possess a common ancestor with the terrestrial one being the most divergent group. The possible origin of triploid morphotypes is discussed. This may highlight the mechanism of L. stolonifera expansion to the new habitats

Issued also as CD