Rachis of the genus Paspalum L. (Poaceae: Panicoideae: Paniceae):

SANDRA S. ALISCIONI; SILVIA S. DENHAM

FLORA

Elsevier

Año: 2008 vol. 203 p. 60 - 76

0367-2530

Infrageneric classification of Paspalum is mainly based on characters of the inflorescence and spikelets. Some of theinflorescence characters usually used are the width and external morphology of the rachises of the racemes.Nevertheless, morphological terminology used in the literature is frequently imprecise. We examine the internalstructure of the rachises of the racemes in Paspalum to: (a) compare it with the anatomy of a vegetative culm,(b) precisely describe its variation within the genus to search for features that could be used in taxonomy or phylogeny.Species representative of all subgenera and informal groups were studied. Serial transversal sections were made andanalyzed using light microscopy.Many distinctive characters from the central keel and lateral wings allow to distinguish six anatomical types ofrachises: Type I is the most frequent in the genus, being present in species of all subgenera; Type II characterizesConjugata, Dissecta and Disticha groups; Type III is exclusive of subgenus Harpostachys; Type IV is common inCeresia subgenus and it is also present in two species of Gardneriana group and in Paspalum guttatum of Erinathagroup; Type V is present in Bonplandiana and Racemosa groups, and Type VI is exclusive of Paspalum falcatum ofFalcata group. Rachises of the racemes are undoubtedly caulinar structures although many species present flatrachises, with vascular bundles arranged in one only row and with abundant photosynthetic tissues. This study permitsto differentiate, by means of anatomical characters, rachises that are morphologically similar or undistinguishable.Some anatomical types of rachises are related to taxonomic groups or subgenera, stressing their taxonomic value.Using anatomical characters of the rachis of the Paspalum raceme can improve phylogenetic analyses.