Resumen

CAMPBELL, Lisa M  y  STEVENSON, Dennis W. Anatomía vegetativa de Aratitiyopea  lopezii (Xyridaceae). Acta Bot. Venez. [online]. 2005, vol.28, n.2, pp.395-408. ISSN 0084-5906.

The center of generic diversity of the monocot family Xyridaceae is northern South America, where four of the five genera are endemic. Many species of these four small genera have restricted distributions and have not been critically studied, including the monospecific genus Aratitiyopea. Populations of this unusual Xyridaceae occur in mid-elevation, forested montane sites. Most Xyridaceae occur in exposed habitats, and although they are at least seasonally wet, many species exhibit xeromorphic adaptations. In contrast, Aratitiyopea presents a morphology and internal anatomy of a mesophyte (trailing stems, leaves with a relatively broad lamina, little mechanical tissue, and lacking a hypodermis, the latter two features present in other Xyridaceae with bifacial leaves) as well as effects of seasonal drying (cell death in the root and thickened endodermal cell walls). Structural details of the vegetative body of Aratitiyopea are presented here, and compared to that known for other Xyridaceae. Although the "gestalt" of Aratitiyopea is aberrant in Xyridaceae, it is structurally consistent with the family, and unusual features are interpreted as adaptations to its habitat, which few other Xyridaceae occupy.

Palabras clave : Xyridaceae; Aratitiyopea; Guiana Shield; Guayana; Mesophyte; Vegetative anatomy; Xerophyte.