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Little is known about vegetative morphological diversification in Neotropical plant clades in comparison with diversification of reproductive characters. Phylogenetic relationships of the Neotropical Heliotropium (Heliotropiaceae) were studied using sequences of nrITS and four plastid regions (trnL-trnF, trnS-trnG, trnH-psbA, rps16). Vegetative morphological diversity (leaf morphology, habit), measured as amount of morphospace occupied and as variance of individual characters, was compared among the clades resolved and between groups of species inhabiting dry and humid areas. Three well-supported clades were recovered: (1) Heliotropium sect. Heliothamnus from the tropical Andes; (2) Heliotropium sect. Cochranea from the Peruvian and the Atacama Deserts; and (3) the Tournefortia clade, comprising the remaining American sections of Heliotropium and the mainly Neotropical Tournefortia sect. Tournefortia. Phylogenetic discordance detected between the plastid and nuclear partitions may have been due to lineage sorting, hybridization or differences in number of informative sites. Morphological diversity was largest in the Tournefortia clade and tended to be greater in dry than in humid areas, but without statistical support. Heliotropium sect. Cochranea was as diverse as the Tournefortia clade in leaf morphology and may have experienced adaptive radiation in the Atacama Desert. Lowest vegetative diversity was found in Heliotropium sect. Heliothamnus. The infrageneric delimitation in Heliotropium needs reassessment.

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Extreme arid conditions in the Atacama Desert in northern Chile have created a unique vegetation almost entirely restricted to the desert margins along the coast of the Pacific Ocean and the Andean range. In this study we provide data on the desert vegetation along elevational gradients at four localities from the western Andean slopes, between 19˚and 21˚S. Additionally, zonation of floristic data was explored. Three altitudinal zones could be classified and described in detail for each locality. Conspicuously divergent floras in the Atacama Desert have been recorded in the coastal 'lomas formations' and in the Andean desert vegetation, separated by a narrow band of absolute desert. In this study, we investigate the floristic relationships between both regions by implementing similarity analyses for 21 localities from the coastal and Andean deserts in northern Chile. Our results show a drastic east-west divergence in pairwise floristic similarity, which is in stark contrast to a weaker north-south divergence. A biotic barrier, preventing plant exchange from east to west and vice versa, imposed by the hyperarid conditions of the absolute desert, is one possible explanation for this finding. Moreover, the coastal and Andean deserts likely represent ecologically divergent habitats, e.g., in rainfall seasonality. Essential differences in factors determining plant life between both regions have probably contributed to a divergent evolution of the floras. Both explanations-ecological divergence and ecogeographical isolation-are not mutually exclusive, but likely complementary. We also combined floristic data from northern Chile and southern Peru. Similarity analyses of this combined dataset provide first floristic evidence for the existence of a biotic north-south corridor along the western slope of the Andes. Sub-Andean distributions of several species are discussed in the light of floristic connectivity between the Peruvian and Chilean Andean floristic clusters.

We present a revision of Lithospermum for South America based on extensive field work and herbarium study which leads to the recognition of ten species including five new to science: Lithospermum bolivariensis, L. cuzcoensis, L. leymebambensis and L. rodriguezii from Peru, and L. azuayensis from Ecuador. The South American species group is morphologically heterogeneous and includes a wide range of growth forms, pollen types and corolla shapes. Molecular data indicate that the species from Ecuador, Peru and Bolivia are monophyletic (South American species group) and represent the sister group of Mexican L. distichum. Lithospermum mediale, disjunct between Colombia/Venezuela and Guatemala/Mexico, represents an independent introduction to South America. Diversification of Andean Lithospermum appears to have progressed from South to North, with the basal taxa being present in the high Andes of southern Peru. The bulk of the species is concentrated in the Amotape‐Huancabamba Zone (northern Peru to southern Ecuador), with five neo‐endemic species being restricted to this area. Lithospermum apparently arrived in the Central Andes ca. 5 Ma and subsequently migrated and diversified northwards, possibly parallel to the uplift of the northern Andes.