Structure and ontogeny of the pericarp of six Eupatorieae (Asteraceae) with ecological and taxonomic considerations

Juliana Marzinek,Denise M.T. Oliveira

doi:10.1590/s0001-37652010000200004

Abstract

The ontogeny of cypselae and their accessory parts were examined using light and scanning electron microscopy for the species Campuloclinium macrocephalum, Chromolaena stachyophylla, Mikania micrantha, Praxelis pauciflora, Symphyopappus reticulatus, and Vittetia orbiculata, some of these being segregated from the genus Eupatorium. A layer of phytomelanin observed in the fruit appears to be secreted by the outer mesocarp into the schizogenous spaces between the outer and inner mesocarp; its thickness was observed to vary among the different species examined. The bristles of the pappus are vascularized, except in M micrantha, and have cells that are superficially projected and arranged acropetally; in S. reticulatus some of the projections are retrorse and a fracture line on the floral disk that is only seen in this species may indicate a double dispersal process. Numerous differences observed among the cypselae examined here reinforce earlier segregations of the genus Eupatorium sensu lato.

Highlights

The tribe Eupatorieae (Asteraceae) comprises 190 genera and 2,000 species (Anderberg et al 2007) that are encountered primarily in Mexico and Central and South America, with some representatives from North America, but with few species in the Old World (King and Robinson 1987)
One character that stands out in descriptions of the cypselae of the Heliantheae s.l. is their dark appearance (Anderberg et al 2007). This aspect can be attributed to the deposition of a rigid layer of phytomelanin, an organic material that fills the schizogenous space of the pericarp during the development of the cypsela after fertilization
Campuloclinum macrocephalum (Fig. 3), Ch. stachyophylla, P. pauciflora, and V. orbiculata have two layers in the outer mesophyll, while five to six cell layers are observed in M. micrantha (Fig. 6) and S. reticulatus (Fig. 4)

Summary

Introduction

The tribe Eupatorieae (Asteraceae) comprises 190 genera and 2,000 species (Anderberg et al 2007) that are encountered primarily in Mexico and Central and South America, with some representatives from North America, but with few species in the Old World (King and Robinson 1987). Wagenitz (1976) suggested that anatomical studies of the fruits of the Asteraceae might aid in elucidating its systematics. Marzinek et al (2008) took into consideration many anatomical and historical aspects of Asteraceae fruits, especially their complex origin, and reaffirmed their true nature as cypselae. (which includes Eupatorieae) is their dark appearance (Anderberg et al 2007). This aspect can be attributed to the deposition of a rigid layer of phytomelanin, an organic material that fills the schizogenous space of the pericarp during the development of the cypsela after fertilization

Methods

Results

Conclusion