Species complexes in Solanaceae: a review of worldwide researches and a case study of the genus Metternichia

Abstract

Solanaceae is a diverse, economically important and taxonomically challenging botanical family. It has many lineages known as species complexes, that is, taxa with unclear taxonomic boundaries due to their intricate evolutionary history and the limitations of the scientific methods applied to delimit them. Based on this, this MSc thesis aimed to explore species complexes in Solanaceae through a revision work and a case study. The revision article intended to generate an overview on how species complexes studies have been conducted in the family by collecting scientific works published until September 2021 and extracting key information from them. Among our results, we observed that: the majority of studies focused on Solanum, the most diverse genus of Solanaceae, with studies around the globe, many of them comprising cultivated taxa; the Neotropical realm as the region that concentrates the majority of studies; Capsicum as having species complexes used analogous to an infraspecific classification; morphometrics, population genetics, chemotaxonomy and reproductive biology as the most scientific fields used to examine species complexes; and Solanum nigrum complex as potentially the most challenging non solved species complex of Solanaceae currently. Our case study focused on evaluate the circumscription of Metternichia principis through the use of integrative taxonomy. The species, restricted to Brazil, was circumscribed as having two varieties based mainly on differences on flower and pollen traits and geographic distribution. Metternichia principis var. macrocalyx would present bigger pollen grains and calyx than the typical variety, with occurrence in arid regions, especially in Caatinga, while Metternichia principis var. principis would be characteristically from humid forests of eastern Brazil. This categorization, however, was based on few individuals and did not analyze fruit and seed characters. We collected bioclimatic, phenological, morphometric and palynological data to be analyzed, mainly, under univariate and multivariate statistical tests. Our results showed a strong differentiation among the varieties regarding environmental data, unveiling contrasting ecological niches. Also, morphometric and palynological multivariate analyses showed a tendency for separation, while univariate tests highlighted key characters to differentiate the varieties, with M. principis var. macrocalyx having bigger flower and pollen traits and smaller fruit and seed traits compared to the typical variety. We also detected a degree of phenological asynchrony among the varieties. Given the strong statistically supported differentiation among the groups, we decided to recircumscribe M. principis var. macrocalyx as being a distinct species from M. principis var. principis.