Peripheral Isolation and the Origin of Diversity in Lepechinia sect. Parviflorae (Lamiaceae)

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Abstract
Both widespread and endemic species occur in Lepechinia sect. Parviflorae. The endemic species occur in southern Ecuador and northern Peru (the Huancabamba Deflection), a region relationship be characterized by highly dissected mountain ranges with deep, dry valleys. The relationship between phylogenetic pattern and historical process in interpreting these patterns of endemism is discussed. Results from cladistic analyses suggest that the endemic species are a more recently evolved group than are the widespread species. It is suggested that climatic fluctuations during the Pleistocene (cooler and drier glacial episodes alternating with warmer and wetter inter-glacials) resulted in periodic range contractions and expansions of Lepechinia populations and subsequent speciation. It is hypothesized that the phylogenetic pattern and historical process supports a peripheral isolate model of speciation.