Phylogeny of <Emphasis Type="Italic">Gunnera</Emphasis>

 The phylogeny of the genus Gunnera is investigated for the first time. Twelve species representing the six currently recognised subgenera are analysed. Two chloroplast DNA regions, the rbcL gene and the rps16 intron, together provide 46 informative characters out of 2335. A combined analysis of both genes gives four most parsimonious trees, firmly establishing the east South American G. herteri as sister group to the rest of the genus. The African G. perpensa is sister group to two well-supported clades, one including the South American subgenera Misandra and Panke, the other the Australian/New Zealand/Malayan species of subgenera Milligania and Pseudogunnera. Thus, South America is a composite area for Gunnera, showing up at two different levels in the cladogram. Our analysis supports a close biogeographic relationship between Australia and New Zealand. The evolution of some morphological characters is discussed. Lastly, the unusual structure of some of the rbcL sequences is reported. Received July 6, 2000 Accepted October 24, 2000     

Intra‐individual variation of flowers in Gunnera subgenus Panke (Gunneraceae) and proposed apomorphies for Gunnerales

A study of inflorescence and flower development in 12 species from four of the six subgenera of Gunnera (Gunneraceae) was carried out. In the species of subgenus Panke, initiation of floral apices along the partial inflorescences is acropetal but ends up in the late formation of a terminal flower, forming a cyme at maturity. The terminal flower is the largest and the most complete in terms of merosity and number of whorls and thus it is the most diagnostic in terms of species‐level taxonomy. The lateral flowers undergo a basipetal gradient of organ reduction along the inflorescence, ranging from bisexual flowers (towards the distal region) to functionally (i.e. with staminodia) and structurally female flowers (towards the proximal region). Our results show that the terminal structure in Gunnera is a flower rather than a pseudanthium. The terminal flower is disymmetric, dimerous and bisexual, representing the common bauplan for Gunnera flowers. It has a differentiated perianth with two sepals and two alternate petals, the latter opposite the stamens and carpels. Comparisons with other members of the core eudicots with labile floral construction are addressed. We propose vegetative and floral putative synapomorphies for the sister‐group relationship between Gunneraceae and Myrothamnaceae. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 262–283.     

Population history of Manihot esculenta (Euphorbiaceae) inferred from nuclear DNA sequences

The nature of gene flow in plants -- including the propensity for interspecific introgression -- makes them interesting candidates for phylogeographical analysis. Plant phylogeography studies have been limited, however, by the availability of suitable intraspecific variation. In this study, DNA sequence variation from a nuclear gene [Glyceraldehyde 3-phosphate dehydrogenase; (G3pdh)] was used to examine the population history of Manihot esculenta ssp. flabellifolia and a potentially hybridizing species, M. pruinosa. These species occur in the rainforest-savanna ecotone adjoining the Amazon basin, a region believed to have undergone major habitat shifts since the Pleistocene. Geographical distributions of the G3pdh haplotypes indicate genetic isolation-by-distance across the range of M. esculenta ssp. flabellifolia. However, there is greater genetic similarity between northeastern and western populations than would be expected given the present species distribution. A nested clade analysis suggests that northeastern and western populations were connected by gene flow until relatively recently, when they became fragmented. This inferred fragmentation event is consistent with post-Pleistocene habitat shifts proposed for the Amazon basin. At the interspecific level, haplotype sharing with M. pruinosa may reflect either recent interspecific introgression or incomplete lineage sorting between these closely related species.     

An investigation into the role of light during desiccation of three angiosperm resurrection plants

Under water‐limiting conditions excitation energy harnessed by chlorophyll can lead to the formation of reactive oxygen species (ROS). Resurrection plants minimize their formation by preventing the opportunity for light–chlorophyll interaction but also quench them via antioxidants. Poikilochlorohyllous species such as Xerophyta humilis break down chlorophyll to avoid ROS formation. Homoiochlorophyllous types retain chlorophyll. We proposed that leaf folding during drying of Craterostigma wilmsii and Myrothamnus flabellifolius shades chlorophyll to avoid ROS (Farrant, Plant Ecology 151, 29–39, 2000). This was tested by preventing leaf folding during drying in light. As controls, plants were dried without light, and X. humilis was included. Craterostigma wilmsii did not survive drying in light if the leaves were prevented from folding, despite protection from increased anthocyanin and sucrose and elevated antioxidant enzyme activity. Membranes were damaged, electrolyte leakage was elevated and plastoglobuli (evidence of light stress) accumulated in chloroplasts. Restrained leaves of M. flabellifolius survived drying in light. Leaf folding allows less shading, but the extent of chemical protection (anthocyanin content and antioxidant activity) is considerably higher in this species compared with C. wilmsii. Chemical protection appears to be light regulated in M. flabellifolius but not in C. wilmsii. Drying in the dark resulted in loss of viability in the homoiochlorophyllous but not the poikilochlorophyllous species. It is hypothesized that some of the genes required for protection are light regulated in the former.     

An overview of the biology of the desiccation-tolerant resurrection plant Myrothamnus flabellifolia

BACKGROUND: Myrothamnus flabellifolia is unique as the only woody resurrection plant. It is an important plant in southern Africa because of its widespread occurrence and usage in African medicine and traditional culture. Many reports have investigated facets of its biology and the mechanisms associated with its desiccation tolerance. SCOPE: The general biology of the woody resurrection plant Myrothamnus flabellifolia is reviewed. The review focuses on the geography and ecology, systematic placement, evolution, morphology and reproductive ecology of M. flabellifolia as well as the wood anatomy and re-filling mechanism. In addition, the desiccation tolerance, ethnobotanical importance and medicinal properties of the plant are reviewed. Also, future research avenues are suggested, in particular the necessity to research the biogeography and systematics of the species and the role of the polyphenols present, as well as the molecular basis of the plant's desiccation tolerance.