Gisekia (Gisekiaceae): phylogenetic relationships, biogeography, and ecophysiology of a poorly known C4 lineage in the Caryophyllales.

PREMISE OF THE STUDY: Gisekiaceae are a monogeneric family of the core Caryophyllales distributed in arid regions of Africa and Asia. The only widespread species of the genus, Gisekia pharnaceoides, performs C4 photosynthesis based on CO2 compensation point measurements. This study investigates the C4 syndrome and its evolution in Gisekia. The infrageneric relationships, distribution and bioclimatic preferences of Gisekia are also investigated. METHODS: Leaf gas exchange characteristics, activity of Rubisco and major C4 cycle enzymes, and ultrastructural characteristics of mesophyll and bundle sheath cells are studied for Gisekia pharnaceoides. δ(13)C values and leaf anatomy are analyzed for all species. A dated molecular phylogeny of 39 accessions representing all species of Gisekiaceae and 14 representatives of closely related core Caryophyllales families is generated using four cp markers and ITS. The precise current distribution and bioclimatic niche of Gisekia is assessed on the basis of 520 georeferenced specimen localities. KEY RESULTS: All traditionally recognized species of Gisekia are C4 plants with atriplicoid Kranz anatomy. Gisekia pharnaceoides uses the NAD-ME biochemical type. The molecular phylogeny demonstrated two East African clades nested within South African clades, demonstrating migration along the arid areas of eastern Africa during the Late Miocene/Pliocene Epochs. Most traditionally defined species are polyphyletic. CONCLUSIONS: Gisekia represents an isolated C4 lineage within core Caryophyllales dating back to the Miocene Epoch and probably spread along the African arid corridor from a South African center of origin. The seven currently recognized species should be treated as one polymorphic species or species complex, Gisekia pharnaceoides agg.

"Trees Live on Soil and Sunshine!"--Coexistence of Scientific and Alternative Conception of Tree Assimilation.

Successful learning is the integration of new knowledge into existing schemes, leading to an integrated and correct scientific conception. By contrast, the co-existence of scientific and alternative conceptions may indicate a fragmented knowledge profile. Every learner is unique and thus carries an individual set of preconceptions before classroom engagement due to prior experiences. Hence, instructors and teachers have to consider the heterogeneous knowledge profiles of their class when teaching. However, determinants of fragmented knowledge profiles are not well understood yet, which may hamper a development of adapted teaching schemes. We used a questionnaire-based approach to assess conceptual knowledge of tree assimilation and wood synthesis surveying 885 students of four educational levels: 6th graders, 10th graders, natural science freshmen and other academic studies freshmen. We analysed the influence of learner's characteristics such as educational level, age and sex on the coexistence of scientific and alternative conceptions. Within all subsamples well-known alternative conceptions regarding tree assimilation and wood synthesis coexisted with correct scientific ones. For example, students describe trees to be living on "soil and sunshine", representing scientific knowledge of photosynthesis mingled with an alternative conception of trees eating like animals. Fragmented knowledge profiles occurred in all subsamples, but our models showed that improved education and age foster knowledge integration. Sex had almost no influence on the existing scientific conceptions and evolution of knowledge integration. Consequently, complex biological issues such as tree assimilation and wood synthesis need specific support e.g. through repeated learning units in class- and seminar-rooms in order to help especially young students to handle and overcome common alternative conceptions and appropriately integrate scientific conceptions into their knowledge profile.