True Black nightshades: phylogeny and delimitation of the Morelloid clade of Solanum

Abstract

The Morelloid clade of Solanum, also known as the black nightshades or Maurella (Morella), is one of the 10 major clades within Solanum. The pantropical clade consists of ca. 76 non-spiny herbaceous and suffrutescent species with simple or branched hairs with or without glandular tips, with a centre of distribution in the tropical Andes. Although the core members of the clade have long been recognised, complete circumscription of the Morelloid clade has remained elusive. Here we provide the first detailed molecular study of the clade. Plastid (trnT-F intergenic spacers), nuclear ribosomal ITS, and low-copy nuclear (waxy) data show three of the four previously unplaced taxa loosely associated with the Morelloids to be placed outside (S. anomalostemon, S. valdiviense, S. reductum), whilst S. salicifolium, a species previously associated with the Dulcamaroid clade, is found to be nested within the group. Four monophyletic groups within the Morelloids can be recognised: (1) Black nightshade clade, including all members of S. sect. Solanum, S. sect. Campanulisolanum, branched-haired taxa, S. salicifolium, and S. triflorum; (2) Episarcophyllum clade, including most members of S. sect. Episarcophyllum; (3) Chamaesarachidium clade, including members of S. sect. Chamaesarachidium; and (4) Radicans clade, including four species from S. sect. Parasolanum. Incongruence between nuclear and plastid gene trees is discussed in relation to known ploidy level variation across the Morelloid clade, especially the African species often referred to as the S. nigrum complex. A new, revised circumscription of the Morelloid clade is provided together with morphological characterisations of the monophyletic clades recovered within it. A preliminary checklist of accepted names for Morelloids is also presented.