The extensive diversity of the tribe Orobancheae, the most species-rich lineage of holoparasitic Orobanchaceae, is concentrated in the Caucasus and Mediterranean regions of the Old World. This extant diversity has inspired hypotheses that these regions are also centres of origin of its key lineages, however the ability to test hypotheses has been limited by a lack of sampling and phylogenetic information about the species, especially in the Caucasus region. First, we assessed the phylogenetic relationships of several poorly known, problematic, or newly described species and host-races of four genera of Orobancheae occurring in the Caucasus region–Cistanche, Phelypaea, Phelipanche and Orobanche–using nuclear ribosomal (ITS) and plastid (trnL–trnF) sequence data. Then we applied a probablistic dispersal-extinction-cladogenesis model of historical biogeography across a more inclusive clade of holoparasites, to explicitly test hypotheses of Orobancheae diversification and historical biogeography shifts. In sum, we sampled 548 sequences (including 196 newly generated) from 13 genera, 140 species, and 175 taxa across 44 countries. We find that the Western Asia (particularly the Caucasus) and the Mediterranean are the centre of origin for large clades of holoparasitic Orobancheae within the last 6 million years. In the Caucasus, the centres of diversity are composed both of long-branch taxa and shallow, recently diversified clades, while Orobancheae diversity in the Mediterranean appears to represent mainly recent diversification.

A new, probably endemic species, Orobanche mlokosiewiczii (Orobanchaceae) is described from Georgia, in the Greater Caucasus. The species grows near waterfalls, on slopes with thermo-hygrophilous subalpine tall herbaceous vegetation, and is exclusively parasitic of another endemic species: Aconitum cymbulatum. It is a graceful whitish or pale white-yellow plant, characterised by campanulate flowers and usually a very wide open throat of corolla. So far, for the Orobanche parasite on Aconitum (exlusively A. lycoctonum) only one species O. lycoctoni is known—occurring in the Cantabrian Mts. in Spain and in the Alps. A detailed description, diagnosis, illustrations, and comparison with possible related species (O. lycoctoni, O. krylowii, O. inulae, O. flava subsp. cicerbitae) are provided. We also present phylogenetic analysis, and nomenclatural notes about the above species, and a lectotype of O. inulae is designated. Moreover, inside the Orobanche sect. Orobanche, a new combination Orobanche subsect. Curvatae and a new series Orobanche ser. Krylowianae are proposed and their types are designated.

Several parasitic plants are known to have acquired mitochondrial genes via a horizontal transfer from their hosts. However, mitochondrial gene transfer in this direction has not yet been found in the parasite-rich family Orobanchaceae. Based on a phylogenetic analysis of the mitochondrial atp6 gene in selected species of Orobanche s.l., we provide evidence of a host-to-parasite transfer of this gene in O. coerulescens, which is a Eurasiatic species that parasitises Artemisia (Asteraceae). We did not find the original Orobanche atp6 gene in this species, which suggests that it has been replaced by a gene that was acquired from Asteraceae. In addition, our data suggest the occurrence of a second HGT event in the atp6 sequence -from Asteraceae to Phelipanche. Our results support the view that the transfer of genetic material from hosts to parasites influences the mitochondrial genome evolution in the latter.

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Orobanche javakhetica (Orobanchaceae) is described as a new, probably endemic, species from the Lesser Caucasus in Armenia. It grows on a subalpine meadow, where it parasitises Lomelosia caucasica (Dipsacaceae). The newly-described species is very characteristic and different from other known Orobanche, however some morphological similarity may exist with species from the Orobanche subsect. Curvatae, particularly with species of the Orobanche series Krylowianae. A detailed description, illustrations, a comparison with the most similar species with identification key, and phylogenetic analysis are provided.