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Tribe Poranthereae is a diverse pantropical group of nine genera and 111 species of desert herbs, temperate shrubs to rainforest trees. Maximum Parsimony and Bayesian Analysis of nuclear ITS and plastid matK regions were combined with traditional taxonomy to gain an understanding of the evolution of the tribe. The results were used to establish a comprehensively revised taxonomic system. Leptopus has been confirmed as an independent genus not directly related to Andrachne. Phyllanthopsis is most closely related to Leptopus and has only a distant relationship to Savia. Zimmermannia and Zimmermanniopsis were shown to be embedded in Meineckia and Oreoporanthera to be embedded in Poranthera. Andrachne sensu lato has been revealed to be polyphyletic, containing a total of five monophyletic lineages with deceptively similar floral morphology. Leptopus is sister to Actephila, forming an Asian clade of forest understorey shrubs to trees. Poranthera forms a Southern Hemisphere clade with Pseudophyllanthus and Notoleptopus. Presence of petals, disc lobe-dissection and seed sculpture were all shown to be homoplasious. Monophyletic clades were found to be better correlated with distribution than with morphological attributes. Each genus and subgenus of the tribe has a distinct ecogeographical profile. There are three New World clades, two Madagascan clades and three Australian clades, probably representing independent radiations. Two genera have been comprehensively treated including species descriptions, keys and Supplied by The British Library - 'The world's knowledge' typification. Three new genera and one new subgenus have been described: Notoleptopus Voronts. & Petra Hoffm., Phyllanthopsis (Scheele) Voronts. & Petra Hoffm., Pseudophyllanthus (MOll.Arg.) Voronts. & Petra Hoffm. and Meineckia subgenus Petaliferae Vororits. & Petra Hoffm. Six new combinations and one nomen novum have been made at the species level. Seven new species-level synonyms have been made, and nine lectotypes were chosen. One species was found to belong outside the tribe. Ten species conservation assessments have been made.

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No description available.

No description available.

Maximum parsimony and Bayesian analysis of the ITS 1&2, tm T-F and 5s rDNA spacer regions was performed for a selection ofmainland and island taxa from the genus Eehium. ITS and tm datasets reveal that both mainland and island taxa separate into two distinct clades. All but two of the island taxa show the characteristic of insular woodiness, suggesting that the evolution of this character may have been a 'key innovation' assisting the diversity ofthe genus on the Macaronesian islands. Lack of basal resolution in the trees generated from the ITS dataset meant that the relative ancestral vs. derived status of these two clades was unclear. Analysis of tm T-F data confirmed the split between mainland and island taxa with the latter being in a derived position in the tree. This is concordant with the results of a number of other studies undertaken for island taxa such as Aeonium, So'!ehus and Argyranthemum. Conflicts ~n the data meant that the combined ITS 1&2 and tm T-F tree was not basally resolved and the question of (', evolutionary polarity was again unclear. Both datasets showed a paucity of characters and lack of I teirninal resolution in the island clade. Hybridisation and long generations time is rejected as a possible cause of this genetic homogeneity and it is concluded that the island EeMa have instead undergone a recent and rapid radiative speciation. Relationships amongst island taxa were similarly unresolved following analysis of clones of the 5s NTS. Given that the 5s region is one of the most rapidly mutating regions of the plant genome, it is concluded that robust cladistic resolution is unlikely to be achievable with single or groups of genes in instances of rapid species radiations. It has been suggested that morphological characters, as direct manifestations of the evolutionary process, are better suited to the study of rapid species radiations. A morphological data matrix for a suite of 25 characters was constructed for Eehium and analysed using maximum parsimony. The perennial difficulty of recognising between convergence and true synapomorphy in morphological characters was highlighted by the paraphyletic nature of the resulting tree in which the mainland/island disjunction defined by molecular analyses was distorted and several outgroup taxa were placed deep within the ingroup. The validity of defming taxic relationships based on morphology in Eehium is therefore considered questionable. The implication associated with the lack of genetic variation in many island plant groups is discuSsed in the context of recognising conservation priorities. Should this minimal genetic diversity be a cause to reassess the conservation importance of island floras?

In flowering plants twin sperm cells are produced by the male gametophyte to enable double fertilization, which is of vital importance for plant fertility. The process of male gametogenesis depends upon relatively poorly understood mechanisms of gamete cell production, but the male germline-specific R2R3 MYB transcription factor DUO1 is an essential factor in germ cell division and gamete differentiation in Arabidopsis. One major objective of the thesis was to assess the validity of Brewbaker’s evidence that Magnoliaceae possess exclusively bicellular pollen at anthesis. This analysis provided conclusive evidence of the coexistence of polymorphic (bicellular and tricellular) pollen in Magnoliaceae species. Further, the maturation of pollen under increased temperature regimes can significantly accelerate the rate of generative cell division in M. grandiflora. A second major aim was to identify sequence and functional conservation of DUO1 orthologs genes in angiosperms and bryophytes. This study provided further evidence that a supernumerary lysine residue in the DUO1 MYB domain is widely conserved and the sequences and expression of two DUO1 orthologs from moss (Physcomitrella patens) were validated. Arabidopsis, tomato and rice DUO1 orthologs were shown to transactivate Arabidopsis DUO1 target promoters. The expression of angiosperm DUO1 orthologs were able to complement the generative cell division and genetic transmission defects in duo1 mutants, demonstrating conservation of function of DUO1 orthologs in Arabidopsis. The final objective was to investigate the functional conservation of DAZ1/DAZ2–related proteins in other angiosperms. The AtDAZ1 orthologs from Brassica rapa (BrDAZ1) and tomato (SlDAZ1) were able to partially rescue the division and transmission defects of daz1/daz2 double mutant pollen, allowing daz1/daz2 homozygous lines to be established harbouring heterologous DAZ1 transgenes. Collectively, these results show conserved functions for both DUO1 and DAZ1/DAZ2 orthologs, highlighting the important role of the transcriptional network controlled by these male germline-specific regulators in from angiosperms.

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No description available.