Phylogenetic Relationships among Populations of Portulaca okinawensis (Portulacaceae) in the Ryukyu Archipelago of Japan using MIG-seq SNP Dada

Portulaca okinawensis Walker et Tawada (Fig. 1A) occurs in rocky coastal environments with pebbly substrates or rock crevices. The species is endemic to the central part of the Ryukyu Archipelago in Japan (hereafter the Ryukyus), which includes the Amami and Okinawa island groups (Fig. 2) (Walker and Tawada, 1951; Hatusima, 1975; Shinjo and Shinzato, 2006; Kokubugata et al., 2013, 2016, 2021). This species was described based on the type specimen collected from Okinawa Island in the Okinawa island group (Walker and Tawada, 1951). Thereafter, Kokubugata et al. (2013) distinguished plants from the Okinawa and Amami island groups based on petal and stem color: the former has dark yellow petals and reddish-green stems, whereas the latter has lemon-yellow petals and light green stems (Fig. 1). Based on these morphological differences, Kokubugata et al. (2013) treated the plants from the Amami island group as an independent variety, namely P. okinawensis var. amamiensis Kokub., Koh Nakam. et Yokota (Fig. 1B), based on the type specimen collected from Amami Island. In the conservation context, this species is rarely found in the wild, and is listed as threatened on the Japanese Red List (Ministry of Environment of Japan, 2020).In previous studies, we confirmed the monophyly of the two varieties by molecular phylogenetic analyses using the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA (Kokubugata et al., 2013, 2016, 2021). Although the ITS region is useful for taxonomically distinguishing the two varieties, it lacks the degree of polymorphism required to understand the phylogenetic relationships among populations of P. okinawensis. Revealing the population relationships would help understanding the historical development of the species distribution. We thus conducted phylogenetic analyses using multiplexed inter simple sequence repeat genotyping by sequencing (MIG-seq; Suyama and Matsuki, 2015) to clarify the phylogenetic relationships among populations of the two varieties of P. okinawensis.