A reappraisal of the genus Megacaryon (Boraginaceae, Lithospermeae) based on molecular, morphological, and karyological evidence

Abstract

The systematic position and phylogenetic relationships of Echium orientale, a rare endemic of the mountains of northern Turkey, were elucidated based on morphological, molecular, and karyological evidence.Using nuclear and plastid DNA sequences, we found that this species is not included in Echium, but is rather at least as divergent from it as other related lineages, namely the South African Lobostemon and Echiostachys. Pollen characters revealed a strong affinity with Onosma, especially in the non-reticulate ornamentation of the tectum. Fruit morphology is unique in the genera of the Echium 'alliance' (e.g. Echium, Pontechium, Lobostemon, and Echiostachys), because of the large size and the smooth, glossy nutlet surface as in most species of Onosma. Karyological observations show that this species is diploid with 2n D 12, and differing from both Lobostemon or Echium, where nearly all species have higher numbers (usually 2n D 14 and 2n D 16, respectively). Combined with a 'megaherb' habit, the weak zygomorphism of the large flowers and a restricted range in the humid mountain forests of the Black Sea region, fruit, pollen and chromosome characters suggest an isolated position for E. orientale in the Echium alliance. We therefore propose its placement in the monotypic Megacaryon, a genus originally described by Boissier, but largely disregarded by later botanists. An original specimen is designated as generic lectotype.

Molecular phylogeny and divergence times of Onosma (Boraginaceae s.s.) based on nrDNA ITS and plastid rpl32‐trnL(UAG) and trnH–psbA sequences

“…Podonosma (O. orientalis). This species appears to be clearly distinct from Onosma and more closely related to Alkanna, confirming the findings of previous molecular studies (Cecchi and Selvi 2009, Weigend et al 2009, Nazaire and Hufford 2012, Cohen 2013, Selvi et al 2017, except for the ISSR analysis of Mehrabian et al (2011). Its close affinity with Alkanna is also supported by morphological traits such as subhorizontally incurved nutlets with a small stiphate areole, gynobase with four cartilaginous cushion-like lobes and ovoid, tricolporate pollen grains (Johnston 1954, Cohen 2013, Binzet et al 2014.…”