# Allotetraploid Origin and Putative Ancient Introgression in Plantago hakusanensis (Plantaginaceae)

## TL;DR

This study investigates the evolutionary history of the endangered Japanese plant Plantago hakusanensis and suggests it may have exchanged chloroplast DNA with a related species.

## Contribution

The study provides molecular evidence for chloroplast capture and clarifies the phylogenetic position of Plantago hakusanensis.

## Key findings

- Plantago hakusanensis is closely related to Plantago asiatica var. densiuscula.
- Chloroplast haplotypes suggest introgression between the two species.
- Nuclear markers indicate monophyly of Plantago hakusanensis.

## Abstract

Plantago hakusanensis (2n = 4x = 24) is an endangered endemic species that occurs in subalpine zones in Japan. To clarify the unresolved phylogenetic position of
P. hakusanensis
within subgenus Plantago, we constructed a phylogenetic tree based on the nuclear‐encoded single‐copy gene sucrose–proton symporter 1 (SUC1) using 60 previously reported alleles from 24 taxa in subgenus Plantago. We found that
P. hakusanensis
was closely related to
Plantago asiatica
var. densiuscula. The phylogenetic relationships between
P. hakusanensis
and
P. asiatica
var. densiuscula were further examined by analyses of the SUC1 nuclear regions and the internal transcribed spacer (ITS) of rDNA, genome‐wide single‐nucleotide polymorphism genotyping (via multiplexed inter‐simple sequence repeat genotyping by sequencing), as well as by additional analyses of three chloroplast (cp) regions (trnL‐F, ndhF‐rpl32, and rpl32‐trnL) in 25 individuals of
P. hakusanensis
and 53 individuals of
P. asiatica
var. densiuscula covering the species' geographical distribution. Monophyly of
P. hakusanensis
was suggested by the nuclear marker analyses, whereas the cp haplotypes of
P. hakusanensis
were shared with
P. asiatica
var. densiuscula and
P. asiatica
in China. The disparity between the nuclear and cp data may be explained by the introgression of the cp genome (cp capture). This research provides a phylogenetic tree showing the position of
P. hakusanensis
within subgenus Plantago and molecular evidence that implies complicated introgressions between
P. hakusanensis
and
P. asiatica
var. densiuscula.

Plantago hakusanensis (2n = 4x = 24) is an endangered endemic species in subalpine zones in Japan.
P. hakusanensis
is closely related to
P. asiatica
var. densiuscula, and each species is monophyletic in terms of nuclear markers, but the chloroplast haplotypes are shared. This disparity may be indicative of chloroplast genome introgression (chloroplast capture) between the two species.