Diversity of metaxylem vessel elements in three Syagrus palms (Arecaceae) of different habits

Vessel elements in Monocotyledons present morphological differences according to the organ where they occur. Usually such diff erences have been explained from an evolutionary perspective, with few data on how the vessel elements could be infl uenced by the diff erent functions of organs and the growth habits of the plants. To address this question, three vegetative organs of palms of the same genus, Syagrus, growing in similar environments, but with different habits, were analyzed. Accordingly, we aimed to detect whether the vessel elements would present similar features in all species or whether the vessel elements would change according to their different habits. We found that the width and type of perforation plates varied in the same way among all species, while the lengths varied in an unusual form. First, all species presented very long elements in the roots, either as long, or longer than those of the stems and leaves. Second, the vessel elements of the stems varied considerably among the species. Specifi cally, in Syagrus romanzoffi ana, vessel elements of the stem were equal in size to those of the other organs, while in both Syagrus fl exuosa and Syagrus petraea, shorter vessel elements were found in the stems. We surmise that vessel elements in palm roots may be related to the high pressure-potential required to avoid stem embolism. The dimorphism of the vessel elements in the stems most likely reflects the distinct habits of these species. Large stems, such as of those of the arboreal palms, presented much longer vessels than those of subterranean stems. Based on these anatomical findings, we suggest that the diff erences found among the vessel elements of roots, stem, and leaves may have evolved in response not only to phylogenetic and ecological constraints, but also to specificities derived from the different plant habits