Anatomy of vegetative organs in Aldama tenuifolia and A. kunthiana (Asteraceae: Heliantheae)

The South American species of the genus Viguiera (Asteraceae) have been transferred to Aldama based on molecular studies. However, the circumscription of Aldama tenuifolia and A. kunthiana has not been well established because the two species are morphologically similar. Both occur in areas of the Cerrado domain, especially in “campos sujos”, “campos limpos” and “campos rupestres”, which are characterised by intense solar irradiation, water scarcity during the autumn and winter, and frequent fires. The aim of the present study is to analyse the anatomy of the vegetative organs of both species in order to identify features that may be useful in their circumscription and in understanding their environmental adaptations. Samples of leaves, stems, xylopodia and roots of each species were collected, fixed, and processed according to the usual methods for light and scanning electron microscopy. The anatomical features useful to delimit the two species are the contours of the epidermal cell walls and in the occurrence of secretory ducts in the primary phloem and fundamental parenchyma of the midrib (leaves), the occurrence of secretory ducts in the primary and secondary phloem (stems) and the degree of cambial activity in the tuberisation process (roots). Regarding the environmental adaptation, both species share the presence of a xylopodium with a high bud shoot-forming potential, fructan accumulation in the tuberised roots, root-mycorrhizal associations, the occurrence of secretory structures, such as glandular trichomes (stems and leaves), internal secretory spaces (roots, xylopodia, stems and leaves) and hydathodes (leaves).