|Sumario:||Background and aims: The morphology and the anatomy of the petioles provide useful information for taxonomic issues in ferns. The aim of this study was to analyze the diagnostic characters of petioles in 37 species of Asplenium that grow in Argentina, to contribute to their identification and to ascertain on their adaptive significance.
M&M: Herbarium specimens and fresh material were employed. Materials were analyzed under stereoscopic and light microscopes; in the latter case, the samples were processed following the conventional histological techniques. The characters analyzed were: colour, length, presence of wings, sub-epidermic mechanical tissue, aeration lines, circumendodermal band (CB), shape and number of vascular bundles and xylem contour.
Results: Some characteristics of the petioles allow the grouping of species. The diagnostic features are: colour, presence/absence of wings, number of vascular bundles, bundles contour, xylem contour and presence/absence of CB.
Conclusions: Petiole characters alone do not allow the identification of the taxa at specific level, although along with others they contribute to the systematics of the genus. The anatomy of the petiole does not show in general terms relationship with the habit of these plants. The type and distribution of subepidermic mechanical tissue and the presence of CB are associated with species that inhabit exposed and dry environments, but these features are not exclusive of the taxa that grow under these conditions.|