Evolution of Impatiens (Balsaminaceae) in the Albertine Rift – The endemic Impatiens purpureoviolacea complex consists of ten species

Abstract

The Albertine Rift harbours a highly diverse flora with numerous endemic species. An important component of the forest understorey is the herbaceous genus Impatiens. Fieldwork in Burundi, the Democratic Republic of the Congo and Rwanda as well as morphological studies indicated that the Albertine Rift endemic Impatiens purpureoviolacea represents a species complex. We analyzed the hidden diversity of the complex using morphological and molecular data supplemented by herbarium studies. We found that the Impatiens purpureoviolacea complex can be divided into morphologically and phylogenetically well characterized clades containing ten species and a natural hybrid. We describe all of these species, provide a species key and analyze their evolutionary history. Beside Impatiens purpureoviolacea and I. gesneroidea, the already described I. urundiensis is resurrected from synonymy. Two varieties, Impatiens purpureoviolacea var. longicalcarata and I. gesneroidea var. superglabra are raised to species status, and five new species (Impatiens elwiraurzulae, I. lotteri, I. ludewigii, I. lutzmannii, I. versicolor) and a new natural hybrid (I. ×troupinii) are described. Within the mostly insect-pollinated species of the clade, two bird-pollinated species (Impatiens gesneroidea, I. superglabra) evolved independently. The clade split from its sister taxon in the Pliocene and started diversifying during the Pliocene/ Pleistocene transition in parallel to an increased mountain uplifting and volcanic activity in the Albertine Rift. It further diversified during the Pleistocene, likely due to the changes in forest cover and connectivity induced by climatic fluctuations.

Pre‐ and postzygotic mechanisms preventing hybridization in co‐occurring species of theImpatiens purpureoviolaceacomplex

“…However, our approach may be applicable to explain the amazing diversity not only in the genus Impatiens but in many other species-rich genera with co-occurring species as well. Ideally, future studies using a similar approach should have a balanced design analyzing the traits of a number I. urundiensis occur geographically close in Burundi (Fischer et al, 2021). These self-compatible but largely pollinator-dependent species are surprisingly variable in their habitats as well as in reproductive and cytological traits, which reflects the distribution of traits in the entire genus (Abrahamczyk et al, 2017;Jeelani et al, 2010;Lozada-Gobilard et al, 2019;Song et al, 2003).…”

“…In these habitats often several, sometimes even closely related Impatiens species occur sympatrically (e.g., Janeček et al, 2015; Kato et al, 1991; Ruchisansakun et al, 2016). However, until now only few natural hybrids have been found (Fischer et al, 2021; Grey‐Wilson, 1980b,c; Tsukaya, 2004). Most of these hybrids occur in disturbed places in small to medium‐sized populations (Grey‐Wilson, 1980b,c).…”

A new, Critically Endangered species of Impatiens (Balsaminaceae) from the coastal plain of the Republic of Congo

“…The current taxonomic framework for continental Africa was established by Grey-Wilson (1980) who recognised 110 species in his monograph. Since then, 24 further species have been published (Abrahamczyk et al 2016; Bos 1991; Cheek and Csiba 2002; Cheek and Fischer 1999; Cheek et al 2022; Fischer 1997; Fischer et al 2003; 2021; Frimodt-Möller and Grey-Wilson 1999; Grey-Wilson 1981; Hallé and Louis 1989; Janssens et al 2009a; 2010; 2011; 2015; 2018; Pócs 2007). The three broad centres of species diversity in tropical Africa are the western African mountains, primarily the Cameroon Highlands (28 species), the E. Arc mountains of Tanzania with the Kenya Highlands (24 species) and the Albertine Rift (20 species) (Fischer et al 2021).…”

Impatiens banensp. nov. &I. etugeisp. nov. (Balsaminaceae), threatened lowland species of the Cross-Sanaga Interval, Cameroon

“…2009a; 2010; 2011; 2015; 2018; Pócs 2007). The three broad centres of species diversity in tropical Africa are the western African mountains, primarily the Cameroon Highlands (28 species), the E. Arc mountains of Tanzania with the Kenya Highlands (24 species) and the Albertine Rift (20 species) (Fischer et al . 2021).…”

“…Since then, 22 further species have been published (Abrahamczyk et al 2016;Bos 1991;Cheek and Csiba 2002;Cheek and Fischer 1999;Fischer 1997;Fischer et al 2003;2021;Frimodt-Möller and Grey-Wilson 1999;Grey-Wilson 1981;Hallé and Louis 1989;Janssens et al 2009a;Pócs 2007). The three broad centres of species diversity in tropical Africa are the western African mountains, primarily the Cameroon Highlands (28 species), the E. Arc mountains of Tanzania with the Kenya Highlands (24 species) and the Albertine Rift (20 species) (Fischer et al 2021).…”