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

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