Phylogeny of Helianthus and related genera

Edward E. Schilling

doi:10.1051/ocl.2001.0022

Abstract

Molecular phylogenetic studies have contributed significantly to our understanding of the phylogenetic relationships of Helianthus, although several problems remain to be resolved. Molecular data have resolved problems with the circumscription of Helianthus. Its sister group is Phoebanthus, a narrowly distributed genus of two species from the state of Florida. The sister group to the Helianthus-Phoebanthus clade is a diverse set of taxa that occurs in Mexico and South America. These include species now classified as part of the paraphyletic Viguiera as well as such distinctive genera as Tithonia, Simsia, Pappobolus, Scalesia, Lagascea, and Alvordia. Incongruence between results based on chloroplast and nuclear-based data sets suggests that hybridization has been involved in the evolutionary history of this group. The nearest outgroup to the clade containing Helianthus is composed of members of Viguiera sect. Maculatae, which are trees and shrubs of Mexico. Other basally diverging groups in the subtribe Helianthinae to which Helianthus belongs are primarily woody members now classified in Viguiera from Mexico and nearby areas. Within Helianthus, divergence appears to be recent, based on an overall lack of divergence between species. The chloroplast-based tree suggests that Helianthus includes four phylogenetic lineages, whereas the nuclear ITS sequence data suggests that the perennial species are paraphyletic relative to the rest of the genus, with basally diverging branches consisting of species confined to the southeastern US. Because there is a lack of divergence among many groups of species, more variable markers will be required to resolve fully relationships within Helianthus.

Highlights

The two genera had never been considered to be related closely with each other. Another puzzle came when we looked at the two South American species of Simsia, which is otherwise found in Mexico and Central America
Chloroplast DNA characters [6], shown on the left of the figure, suggest that there are four major, divergent lineages, and further that Phoebanthus is an ingroup to one of these formed by the perennial species of Helianthus
Helianthus heterophyllus is found along the Atlantic and Gulf coasts, and Helianthus porteri occurs in granite outcrops centered in Georgia

Summary

Introduction

A fourth point is that when we look within Helianthus, we find that all of the species are very similar to each other at the molecular level. The molecular phylogenetic data show that Helianthus is a well-defined group that is clearly placed just within the x = 17 lineage. The South American species that have been placed in the past in Helianthus are all part of a different lineage, and the name Pappobolus is the correct one for them.

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Conclusion