Resolving the taxonomic enigma of Nesocaryum stylosum (Boraginaceae): phylogenetic evidence for its reclassification as Cryptantha stylosa

The classification of <i>Nesocaryum stylosum</i> (Boraginaceae) has remained unresolved for nearly a century. This species is endemic to Isla San Ambrosio, a small island located approximately 900 km due west of the coast of central Chile. Ivan M. Johnston transferred the species from the genus <i>Heliotropium</i> to the monotypic <i>Nesocaryum</i> in 1927 but noted that, despite its quite different and rather unique vegetative, inflorescence, and calyx morphology, its unit fruits (nutlets/eremocarps) resemble those of <i>Cryptantha</i>. Here, we review the morphology and taxonomic history of <i>N. stylosum</i> and provide DNA sequence data that support its placement in <i>Cryptantha</i>, for which we propose the new combination <i>Cryptantha stylosa</i>. Our data also support the placement of this species within the <i>Maritimae</i> clade, a monophyletic group of <i>Cryptantha</i> species that is phylogenetically distinct from the bulk of the genus. We propose an expanded membership of the <i>Maritimae</i> clade comprising up to 19 species: eight species (13 minimum-rank taxa) from North America and 12 species (12 minimum-rank taxa) from South America, including <i>Cryptantha stylosa</i>, with one taxon occurring on both continents. We further review evidence bearing on the biogeographic and evolutionary history of <i>Cryptantha stylosa</i> and its putative closest relatives and identify the need for additional research within the group.