The Hemiparasitic Plant Phtheirospermum (Orobanchaceae) Is Polyphyletic and Contains Cryptic Species in the Hengduan Mountains of Southwest China

Abstract

Phtheirospermum (Orobanchaceae), a hemiparasitic genus of Eastern Asia, is characterized by having long and viscous glandular hairs on stems and leaves. Despite this unifying character, previous phylogenetic analyses indicate that Phtheirospermum is polyphyletic, with Phtheirospermum japonicum allied with tribe Pedicularideae and members of the Ph. tenuisectum complex allied with members of tribe Rhinantheae. However, no analyses to date have included broad phylogenetic sampling necessary to test the monophyly of Phtheirospermum species, and to place these species into the existing subfamiliar taxonomic organization of Orobanchaceae. Two other genera of uncertain phylogenetic placement are Brandisia and Pterygiella, also both of Eastern Asia. In this study, broadly sampled phylogenetic analyses of nrITS and plastid DNA revealed hard incongruence between these datasets in the placement of Brandisia. However, both nrITS and the plastid datasets supported the placement of Ph. japonicum within tribe Pedicularideae, and a separate clade consisting of the Ph. tenuisectum complex and a monophyletic Pterygiella. Analyses were largely in agreement that Pterygiella, the Ptheirospermum complex, and Xizangia form a clade not nested within any of the monophyletic tribes of Orobanchaceae recognized to date. Ph. japonicum, a model species for parasitic plant research, is widely distributed in Eastern Asia. Despite this broad distribution, both nrITS and plastid DNA regions from a wide sampling of this species showed high genetic identity, suggesting that the wide species range is likely due to a recent population expansion. The Ph. tenuisectum complex is mainly distributed in the Hengduan Mountains region. Two cryptic species were identified by both phylogenetic analyses and morphological characters. Relationships among species of the Ph. tenuisectum complex and Pterygiella remain uncertain. Estimated divergence ages of the Ph. tenuisectum complex corresponding to the last two uplifts of the Qinghai–Tibet Plateau at around 8.0–7.0 Mya and 3.6–1.5 Mya indicated that the development of a hot-dry valley climate during these uplifts may have driven species diversification in the Ph. tenuisectum complex.

Parasitic angiosperms: How often and how many?

“…The more recent study by Yu & al. () highlighted the same polyphyletic issue as Dong & al. () but did not follow the taxonomy proposed in Pinto‐Carrasco & al.…”

“…In that chapter, the phylogenetic relationships of the various clades in the family were discussed, and five disconnected phylogenetic trees were shown that included lists of unplaced taxa based on their assumed affinity. Although there have been numerous phylogenetic studies since 2013 (e.g., Schneider & al., ; Uribe‐Convers & Tank, ; Fu & al., ; Pinto‐Carrasco & al., ; Gaudeul & al., ; Yu & al., ; Li & al., ), most have been focused on a particular group (tribe) within Orobanchaceae. It appears that there does not exist in the literature an attempt to incorporate all the available phylogenetic information to produce a “super tree” of Orobanchaceae.…”

“…Yu & al. () included two species of Brandisia and showed moderate support for this clade as sister to tribes Buchnereae, Rhinantheae, and Pedicularideae.…”

“…In contrast, Yu & al. () used nuclear ribosomal ITS sequences to show that this clade diverged later and was sister to the remaining members of the family. This topology places the holoparasitic Orobancheae as sister to the entire family, a result also obtained using low‐copy nuclear genes (Li & al., ).…”

Allopolyploidy in the Wintergreen Group of tribe Gaultherieae (Ericaceae) inferred from low‐copy nuclear genes

“…The species of Leucothoides have their center of diversity in the Himalaya and Hengduan Mountains in East Asia, and the latter in the Andes of South America. These regions are recognized as 'species pump' areas (Terborgh 1992, Jetz et al 2004, with highly variable environmental parameters involving area, elevation, topography and climate (Körner 2004, Tang et al 2006, Schwery et al 2015, Yu et al 2018) promoting hybridization and subsequent (allo)polyploid speciation (Rauscher 2002, Nie et al 2005, Schmidt-Lebuhn et al 2010.…”