From the Mediterranean to the Pacific: re-circumscription towardsNotelaea s.l.and historical biogeography of a generic complex in Oleinae (Oleaceae)

Abstract

Tackling the complicated infrafamilial classification of the economically important Oleaceae requires a piecemeal approach that addresses generic circumscriptions. Here, focusing on the distinct clade formed by the generic complex Nestegis, Notelaea, Osmanthus, Phillyrea, and Picconia within the subtribe Oleinae, we aim to elucidate their boundaries and relationships and to evaluate their biogeographic history in light of their peculiar disjunct distribution in the Macaronesian, Mediterranean, and Pacific Regions. Based on phylogenomic data from plastid and nuclear DNA of an extensive sampling, the results show six subclades within this generic complex, which are also geographic segregates found in Australia (Notelaea), Hawaiian Islands (Nestegis sandwicensis), Macaronesia (Phillyrea and Picconia), Mediterranean Region (Phillyrea), New Caledonia (Osmanthus section Notosmanthus), and New Zealand (Nestegis s.s.). Accounting for broad morphological overlaps within this clade, we recognize three genera (Phillyrea, Picconia, and Notelaea s.l.), subsuming all Pacific taxa under Notelaea s.l. Molecular dating and biogeographic analyses indicate that this clade originated in Eurasia during the Early Miocene (mean 23.2 Mya, 95% HPD: 23.8 -14.7). Finally, dispersal (rather than continental vicariance) is likely the main explanation for the global, disjunct distribution of this group; with island-hopping and local extinction as the hallmarks of its evolutionary history.

Comparative and phylogenetic analysis of the complete chloroplast genomes of Osmanthus (Oleaceae) species

“…Notosmanthus in traditionally morphological classification system. As members of Oleinae subtribe, traditional Osmanthus species did not formed a monophyletic group in our phylogenetic inference, which was consistent with previous studies based on DNA barcodes (Guo et al 2011, Yuan et al 2010, Wallander and Albert 2000, Dupin et al 2022). The phylogenetic position of O. austrocaledonicus, distributed in New Caledonian, appeared to be closer to Notelaea and Nestegis species of NNPPO clade than species of major Osmanthus clade.…”

“…Leiolea and Sect. Notosmanthus were more closely related to species of other genera such as Chionanthus, Olea, Nestegis, Noronhia and so on, rather than Osmanthus species belonging to other three sections (Yuan et al 2010, Guo et al 2011, Dupin et al 2022. Li et al (2020a) suggested that the East Asian Sect.…”

“…Wallander and Albert (2000) reconstructed the phylogenetic tree of Oleaceae family based on trnL-trnF region and rps16 intron, and found that five Osmanthus species were not monophyletic taxa. Subsequently, based on different DNA fragments, more Osmanthus species and closely related species were included in phylogenetic analysis (Yuan et al 2010, Lu et al 2011, Guo et al 2011, Dupin et al 2022, which further determined the polyphyly of 3 genus Osmanthus. The cluster results in these phylogenetic studies showed that the species of Sect.…”

Reticulate evolution of the tertiary relict Osmanthus

“…Notosmanthus . With the application of molecular systematics to this genus, it has been found that Osmanthus is not a monophyletic taxon; for example, sections Leiolea and Notosmanthus have been proven not to belong to Osmanthus (Dupin et al., 2022; Li et al., 2020). While the remaining three sections cannot correctly reflect grouping relationships, our 4‐clade framework provides new insight and suggests that a revision of the sectional classification of Osmanthus is warranted.…”

“…Chang are classified as ‘vulnerable’ or ‘endangered’ due to declining populations (Melia et al., 2012; Qin et al., 2017; Tamar, 2020). The taxonomy of Osmanthus is controversial due to convergent trait evolution among unrelated species or genera, with molecular approaches aiding the delimitation of intergeneric boundaries (Dupin et al., 2022; Li et al., 2020, 2022). However, within the genus, conflicts persist between the nuclear and plastid gene trees, suggesting the existence of reticulate evolution (Guo et al., 2011; Li et al., 2020; Yuan et al., 2010).…”