Secretory duct distribution and leaf venation patterns of Aldama species (Asteraceae) and their application in taxonomy

Abstract

Features of leaf morphology such as secretory duct distribution and venation patterns are important taxonomical tools; however, some species can have variation in these traits. This study evaluates whether the secretory duct distribution in the midrib and venation is similar across different leaves of 17 Aldama species. Six fully expanded leaves (three each of the largest and smallest size) from five distinct plants were selected to analyze the duct distribution. The samples were histologically examined, and the quantitative data were statistically analyzed. The venation pattern was analyzed in five fully expanded leaves of different plants. In all, 23 secretory duct distribution patterns were identified; they showed intra- and inter-species variations except in Aldama anchusifolia (DC.) E.E.Schill. & Panero and A. trichophylla (Dusén) Magenta. The largest number of ducts was not correlated with leaf and midrib dimensions (width and length). Further, Aldama venation could be divided into two groups: (1) pinnate camptodromous brochidodromous type (four species), and (2) acrodromous venation type and its basal and suprabasal variations (13 species). Thus, distinct secretory duct arrangements of the midrib might assist in the discrimination of Aldama species. The venation patterns were also important for distinguishing the majority of species selected.