Distribution of homobaric and heterobaric leafed species in the Brazilian Cerrado and seasonal semideciduous forests

Abstract

Plant species can be classified into heterobaric and homobaric, depending on whether their leaves present bundle sheath extensions (BSEs) (heterobaric) or not (homobaric). Incidences of the two leaf types seem to be related to growth environment and the light stratification. The Brazilian Cerrado and seasonal semideciduous forests are contrasting environments mainly with regard to irradiance and air humidity. However, studies comparing the distributions of homobaric and heterobaric species in these vegetation types are lacking. We investigate the presence/absence of leaf BSEs across diverse habits (herbs, shrubs and trees) in a seasonal semideciduous forest, cerrado sensu stricto (open physiognomy) and cerradão (forest physiognomy) to evaluate the influence of plant habit and growth environment on the distribution of homobaric and heterobaric species. Leaves from 131 species in 54 angiosperm families were analysed using standard methods of light microscopy. The distribution of the different leaf types in each environment was analysed using the χ2 test and Fisher’s exact test (P<0.05). Homobaric and heterobaric leafed species occur in all environments and do not correlate with plant habit. Of the total number of species examined, 103 (78.6%) exhibited homobaric leaves and 28 (21.4%) presented heterobaric leaves. Of the total of heterobaric species, 8.8% occurred in the seasonal semideciduous forest, 50% in the cerradão and 41.2% in the cerrado sensu stricto. This model of distribution may be related to the higher irradiances in Cerrado. Homobaric leaves of shrubs and trees were thicker in all environments, while heterobaric leaves of herbs were thicker in the Cerrado. This study finds a tendency for the distribution pattern of homobaric or heterobaric leaves to reflect both the growth environment and the taxonomic grouping. Since leaf type is a constitutive characteristic, interspecific differences in leaf type may reflect particular physiological behaviours, linking them to success in colonising particular environments.