Structural features of species of Asteraceae that arouse discussions about adaptation to seasonally dry environments of the Neotropics

ABSTRACT

Seasonally-dry environments of the Neotropics, such as the South American Chaco, exert selective pressures on vegetation through a pronounced water deficit. We describe the underground system and leaf anatomy of three species of Asteraceae from the Brazilian portion of the Chaco (Pterocaulon purpurascens Malme, Wedelia trichostephia DC., and Pectis gardneri Baker), aiming to describe their structural and adaptive features using standard plant anatomy techniques. Pterocaulon purpurascens and W. trichostephia exhibited slightly thickened xylopodia, with gemmiferous character and self-grafted stem shoots; Pectis gardneri displayed a slightly-thickened tuberous root with storage substances. Longitudinal sequences of cells with highly thickened walls forming globular protrusions were found throughout the extension of the periderm of Pectis gardneri, while senescent trichomes were found in the periderm of W. trichostephia. Schyzogenous aerenchyma was found in P. purpurascens. Aquifer cells, composing vascular rays of secondary phloem and xylem, are reported for this species. Leaves of the three species are perennial and amphistomatic, with aquifer cells in a variety of tissues. Pectis gardneri exhibits a “Kranz-type” anatomy with lignified bristles with stomata. The features described for the species play important role in water uptake and/or storage, which prevent excessive water loss during environmental or physiological stress periods.

Keywords:
Asteroideae; drought; steppic savanna; underground systems; water stress; xylopodia