Comparative leaf anatomy of two species of Ipomoea L. (Convolvulaceae): taxonomic importance and adaptations to xeric conditions of the cangas

Background: Accurate species identification is the first step towards establishing conservation strategies, especially regarding rare and threatened species, such as those studied here. Moreover, understanding the responses to the environment and growing conditions of endemic species is necessary for its conservation. This study compares the leaf anatomy of Ipomoea cavalcantei and I. marabaensis, which grow on the Brazilian ironstone outcrops (cangas) and exhibit morphological convergence.

Methods: Leaf anatomical characters of the species were described. Additionally, the leaf adaptive potential of I. cavalcantei was evaluated, comparing individuals grown in natural canga areas (in situ) and cultivated in topsoil (ex situ). Quantitative analysis evaluated stomatal density, polar and equatorial diameter of stomata, and thickness of the epidermis and mesophyll.

Results: Ipomoea cavalcantei and I. marabaensis can be distinguished by the mesophyll type. Ipomoea marabaensis is also characterized by the presence of lateral protuberances on the abaxial surface of the midrib. Individuals of I. cavalcantei under cultivation have lower stomatal density, although their functionality (polar/equatorial diameter) is more significant than those grown in a natural environment; these individuals also exhibit leaves with a thinner cuticle, abaxial epidermal cells with more sinuous walls, a lower occurrence of trichomes and secretory cells (laticifers), and more druse-containing idioblasts in the mesophyll. All these traits are adaptations to growing conditions that include lower light and the absence of water stress.

Conclusions: Leaf anatomical traits showed to be useful to delimit Ipomoea cavalcantei and I. marabaensis in the non-reproductive stage. For individuals of I. cavalcantei cultivated in topsoil, some features, especially of the epidermis, respond to light and water supply.