Geographic distributions and physiological characteristics of co-existing Flaveria species in south-central Mexico

The genus Flaveria consists of 23 species with significant variation in photosynthetic physiologies. We tested whether photosynthetic pathway variation in seven co-existing Flaveria species corresponds to geographic distributions or physiological performance in C3, C4, and intermediate species growing under natural conditions in south-central Mexico. We found that Flaveria pringlei (C3) was the most widely distributed species with multiple growth habits. Numerous populations of Flaveria kochiana (C4), a recently described species with a previously unknown distribution, were located in the Mixtec region of Oaxaca. Flaveria cronquistii (C3) and Flaveria ramosissima (C3-C4) were only located in the Tehuacán Valley region while Flaveria trinervia (C4) was widely distributed. Only one population of Flaveria angustifolia (C3-C4) and Flaveria vaginata (C4-like) were located near Izúcar de Matamoros. Midday leaf water potential differed significantly between Flaveria species, but did not vary according to growth habit or photosynthetic pathway. The quantum yield of photosystem II did not vary between species, despite large differences in leaf nitrogen content, leaf shape, plant size and life histories. We did not find a direct relationship between increasing C4 cycle characteristics and physiological performance in the Flaveria populations examined. Furthermore, C3 species were not found at higher elevation than C4 species as expected. Our observations indicate that life history traits and disturbance regime may be the primary controllers of Flaveria distributions in south-central Mexico.