Abstract

ROJAS-LEAL, Alicia; TERRAZAS, Teresa  and  VILLASENOR, José Luis. Venation pattern development in four species of the Senecioneae (Asteraceae). Bot. sci [online]. 2014, vol.92, n.1, pp.23-36. ISSN 2007-4476.

The venation pattern development was described and evaluated during leaf expansion in Packera sanguisorbae, Psacalium peltatum, Roldana angulifolia, and R. lineolata of the Senecioneae tribe (Asteraceae) with contrasting morphologies (round versus elliptical shape, and entire versus deeply lobed lamina). The aims of this study were to identify the changes that occur during the venation pattern development and to determine if lamina shape correlates with the venation pattern. Leaves of different ages from meristematic apexes to fully developed leaves were collected and cleared with a basic fuchsin-NaOH mixture. The results showed that type of margin, dissection of lamina, and the venation pattern (primary and secondary veins) are fixed since early stages of the development, when the lamina counts on 3% of its length. However, lamina shape is acquired later in development. Veins development followed a hierarchical pattern as described for other taxa. However, venation orders varied between lobes and teeth. Lobes are irrigated by primary and secondary veins, while up to 7^th orden veins are found in the teeth. Leaf shape may predict the venation pattern except when the leaf has an elliptic shape. In Packera the festooned semicraspedodromous venation pattern is present in entire or dissected laminas. We conclude that the early establishment of the venation pattern as well as the lamina shape are important characters in the taxonomy of the Senecioneae tribe.

Keywords : leaf expansion; lobes; Packera; Psacalium; Roldana; teeth; venation orders.