Studies on morpholigical and anatomical characters indicating C3 and C4 photosynthetic metabolism in the genus Boerhavia L.in Nigeria
This study investigated leaf morphological and anatomical characters of four species of the genus Boerhavia, known to contain C3 and C4 photosynthetic groups. This was with a view to establishing characters that may be useful in the grouping of the Nigerian species into their respective photosynthetic groups, and also to documentig characters that may be peculiar to dicotyledons. The species investigated were Boerhavia coccinea Mill., B. repens L., B. diffusa L. and B. erecta L. collected from different locations in the southwestern Nigeria. Both qualitative and quantitative morphological as well as anatomical characteristics like inflorescence form and arrangement, stem shape, leaf morphology and venation pattern, plant height, stem length, leaf length, leaf width and petiole length were observed and documented. Other characters observed and documented included stomata index, stomata size, interstomatal distance, stomata density, interveinal distance, vein density and vein distance, intercellular air spaces, leaf thickness, mesophyll thickness, Kranz tissue, one cell distant count and maximum lateral cell count. The results revealed that paniculate inflorescence was a morphological character which delimited C3 from C4 species with cymose inflorescence. All anatomical characters investigated were found to be useful in the grouping of these species along photosynthetic pathways. However, among all the characters examined, interveinal distance of less than 166 µm for C4 and which was greater than 166 µm for C3 was recorded. Maximum lateral count ranging from 2 to 6 for C4 and 5 to 10 for C3 was found to be peculiar to the dicotyledons. The study concluded that with the combination of morphological and anatomical characters, B. erecta, B. coccinea and B. repens were C4 species while B. diffusa was a C3 species.