Format: ORAL

Marcelo R. Pace, Anglica Quintanar Castillo, Camila Alcantara

Universidad Nacional Autónoma de México, Instituto de Biología, Departamento de Botánica

The ancestral habit of woody plants is inferred as self-supporting i.e., either erect shrubs or trees. The vascular system in self-supporting woody plants fulfills the roles of water and photosynthate transport, mechanical support, storage, and longevity. Lianas, however, do not support themselves, therefore their stem anatomy, released from this role, undergo modifications towards other critical purposes. First, lianas have some of the most efficient hydraulic systems, with less fibers, wider and more abundant vessels per unit area. Second, liana stems undergo selection for flexibility, thus their stems have wider and taller rays, sometimes more abundant axial parenchyma, and the wholesale restructuring of the vascular architecture (vascular variants), which intermixes parenchymatous and lignified tissues. Interestingly, within several ancestrally lianescent lineages, self-supporting plants have re-evolved, when occupying semi-arid regions. In these unique cases, the vascular system, therefore, must provide support to keep the stem upright, which is reflected in the reversal to a secondary xylem with narrower vessels, smaller rays and more fibers, and sometimes with changes in the axial parenchyma abundance. Critically, when the self-supporting habit is regained, vascular variants in their stems may even be lost or greatly reduced. Conversely, if the emergent self-supporting habit is succulent, these plants co-opt the ancestral vascular variant for increased water storage, representing a case of exaptation. In this talk, I will discuss the re-emergence of self-supporting plants from ancestrally lianescent lineages using case studies in Bignoniaceae, Convolulaceae, and Malpighiaceae.