Morfoanatomia comparada e ontogênese do pericarpo de Bidens gardneri Baker e B. pilosa L. (Asteraceae)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Neural networks in chemosystematic studies of asteraceae: A classification based on a dichotomic approach

This paper describes the application of artificial neural nets as an alternative and efficient method for the classification of botanical taxa based on chemical data (chemosystematics). A total of 28,000 botanical occurrences of chemical compounds isolated from the Asteraceae family were chosen from the literature, and grouped by chemical class for each species. Four tests were carried out to differentiate and classify different botanical taxa. The qualifying capacity of the artificial neural nets was dichotomically tested at different hierarchical levels of the family, such as subfamilies and groups of Heliantheae subtribes. Furthermore, two specific subtribes of the Heliantheae and two genera of one of these subtribes were also tested. In general, the artificial neural net gave rise to good results, with multiple-correlation values R > 0.90. Hence, it was possible to differentiate the dichotomic character of the botanical taxa studied.

A general survey and some taxonomic implications of diterpenes in the Asteraceae

This paper provides a general survey of the occurrence of diterpenes in the Asteraceae. Data on 4351 botanical occurrences were obtained from the literature. These were grouped by skeleton for each genus. Then, the genera were grouped by subtribes, which, in turn, were gathered in tribes, followed by subfamilies. In spite of the low number of species containing diterpenes, it was possible to describe some structural features of these compounds, i.e. The skeletal types in various taxa and the positions in some skeletons that are always oxidized or never undergo oxidation in some genera. Thus, it was verified that: in the subfamily Cichorioideae, only a few of the studied species possess diterpenes, wherein kaurane is the most frequent diterpene skeleton. In the Asteroideae, the presence of diterpenes is much greater than that in the Cichorioideae and Carduoideae. At tribal taxonomic level, for example, the Astereae produce labdanes and clerodanes; Heliantheae and Eupatorieae produce kauranes and labdanes, respectively; and Calenduleae produce pimaranes. Some taxonomic implications are presented. (c) 2005 the Linnean Society of London.

Self-Organizing Maps of Molecular Descriptors for Sesquiterpene Lactones and Their Application to the Chemotaxonomy of the Asteraceae Family

The Asteraceae, one of the largest families among angiosperms, is chemically characterised by the production of sesquiterpene lactones (SLs). A total of 1,111 SLs, which were extracted from 658 species, 161 genera, 63 subtribes and 15 tribes of Asteraceae, were represented and registered in two dimensions in the SISTEMATX, an in-house software system, and were associated with their botanical sources. The respective 11 block of descriptors: Constitutional, Functional groups, BCUT, Atom-centred, 2D autocorrelations, Topological, Geometrical, RDF, 3D-MoRSE, GETAWAY and WHIM were used as input data to separate the botanical occurrences through self-organising maps. Maps that were generated with each descriptor divided the Asteraceae tribes, with total index values between 66.7% and 83.6%. The analysis of the results shows evident similarities among the Heliantheae, Helenieae and Eupatorieae tribes as well as between the Anthemideae and Inuleae tribes. Those observations are in agreement with systematic classifications that were proposed by Bremer, which use mainly morphological and molecular data, therefore chemical markers partially corroborate with these classifications. The results demonstrate that the atom-centred and RDF descriptors can be used as a tool for taxonomic classification in low hierarchical levels, such as tribes. Descriptors obtained through fragments or by the two-dimensional representation of the SL structures were sufficient to obtain significant results, and better results were not achieved by using descriptors derived from three-dimensional representations of SLs. Such models based on physico-chemical properties can project new design SLs, similar structures from literature or even unreported structures in two-dimensional chemical space. Therefore, the generated SOMs can predict the most probable tribe where a biologically active molecule can be found according Bremer classification.

Plasmopara sphagneticolae sp. nov. (Peronosporales) on Sphagneticola (Asteraceae) in Australia

A specimen of downy mildew on leaves of Sphagneticola trilobata found in northern Queensland was identified by a systematic approach as a novel species of Plasmopara. A new species, Plasmopara sphagneticolae, is proposed for this specimen, which differs from other species of Plasmopara by morphology, host range, and sequence data from nuclear-ribosomal DNA and mitochondrial DNA. Plasmopara sphagneticolae, together with P. halstedii, are downy mildews found on host species in the tribe Heliantheae (Asteraceae). Plasmopara halstedii causes downy mildew on Helianthus annuus, and is not present on sunflower in Australia. Phylogenetic analysis of the large subunit region of ribosomal DNA showed that P. sphagneticolae was sister to P. halstedii on sunflower.