A revision of the endemic Brazilian Solanum hexandrum group (Leptostemonum, Solanum, Solanaceae)

The Leptostemonum Clade, or the 'spiny solanums', represents half of the species diversity of the large cosmopolitan genus <i>Solanum</i> (Solanaceae). Brazil is a centre of both species and lineage diversity in 'spiny solanums' with a number of lineages occurring mostly only there. Here, we treat the <i>Solanumhexandrum</i> group, a monophyletic species group that is part of the larger and unresolved Erythrotrichum clade <i>sensu lato.</i> The six species treated here are all robust very prickly shrubs with amongst the largest and showiest flowers in <i>Solanum</i> and accrescent calyces in fruit that often completely cover the mature berry. All six species are endemic to the coastal Atlantic forests of south-eastern and north-eastern Brazil. We describe one new species, <i>S.phrixothrix</i> Gouvêa & S.Knapp, <b>sp. nov.</b>, known only from two collections made 200 years apart. Many of the species in the group occur in very small populations around isolated gneissic/granitic inselbergs, a highly threatened habitat in the region. We provide complete nomenclatural details for all recognised species and their synonyms, complete descriptions, distributions including maps, illustrations, common names and uses and preliminary conservation assessments.