Pollen characters and DNA sequence data converge on a monophyletic genus Iresine (Amaranthaceae, Caryophyllales) and help to elucidate its species diversity

Borsch T, Flores-Olvera H, Zumaya S, Müller KF

Research article (journal)


Iresine is a neotropical genus of the Amaranthaceae with most of the species diversity in Mexico and Mesoamerica. It has suffered a complex classification history with considerably diverging views on the genus concept. We have carried out a phylogenetic analysis of Iresine and allied genera using sequence data of combined plastid introns (including the matK CDS) and spacers as well as ITS, and a dense sampling of species. Trees depict a clade of Iresine with Irenella and Woehleria deeply nested. This clade is sister to the remainder of Gomphrenoideae including Hebanthe and Trommsdorffia (≡ Pedersenia). One of two maximally supported subclades of Iresine comprises mostly species restricted to the Mexican highlands and adjacent areas, whereas the other subclade is composed of more widespread Mexican-Mesoamerican taxa. Pollen grains of Iresine and relatives were examined using high-resolution SEM, which yielded a matrix of 15 pollen characters. Ancestral character state reconstruction shows dodecahedral grains (in I. angustifolia and I. nigra) to have evolved within the Iresine clade, not involv- ing the complete suite of character shifts associated with metareticulate pollen but just an increase of aperture diameter and a slight decrease of mesoporia width. To the contrary, four character state transformations occurred in the common ancestor of core Gomphrenoideae that led to metareticulate pollen (shifts to a distal orientation of punctae and microspines, to a sunken position of apertures relative to the distal part of mesoporia resulting in narrow mesoporia higher then wide, and a reduction in the diameter of mesoporia). The Iresine clade is characterized by pollen with well-separated ektexinous aperture membrane bodies, rounded or triangular, and gradually tapering into a single spine. For the monophyletic genus Iresine, 35 species are currently accepted. We provide a taxonomic backbone (including one new combination, one new name and several lectotypi- fications) that also comments on the current understanding of species delimitation.

Details zur Publikation

Release year: 2018
Language in which the publication is writtenEnglish