Phylogenetic patterns reflect the interplay of speciation and extinction resulting from complex interactions of organisms with their environment and offer key insight into the processes that have shaped modern biodiversity. However, clarifying patterns of radiation on a global scale and linking those patterns with shifts in distribution, ecology, and morphology are formidable challenges for most large, hyper-diverse lineages of organisms. The advent of powerful new analytic techniques coupled with an ever-increasing ease of accumulating informative sequence data provides the opportunity to construct comprehensive phylogenetic trees that form a conceptual framework for synthesis on a broad scale not previously possible. These advances have also transformed historical biogeography from a field of often speculative narrative to a complex and rigorous discipline that uses sophisticated computational methods to integrate and interpret results from molecular phylogenies, past geological processes, morphological character evolution, lineage diversification hypotheses, and more.
Despite the tremendous recent progress in these disciplines, however, our understanding of how most globally distributed plant lineages have diversified in relation to present landform distribution remains unclear. For example, did they radiate in situ after reaching new areas? Did they radiate in parallel in different areas following regional or worldwide climatic shifts? Due to their worldwide distribution, wide array of growth forms, occurrence in diverse environments, as well as unique chemical and morphological innovations, Lamiaceae (mints) are an excellent model clade to investigate how historical climatic and geologic processes, as well as the evolution of key morphological traits, have shaped present species distribution.
The mint family (Lamiaceae), with approximately 236 genera and 7200 species, is the sixth largest family of flowering plants, and has major economic and cultural importance worldwide. While the Lamiaceae has been recognized as a family for centuries, the family was only recently defined in its current broad sense (Cantino & Sanders 1986; Cantino 1992; Wagstaff et al. 1995, 1998; Wagstaff & Olmstead 1997; Harley et al. 2004; see also Junell 1934 for an earlier and very similar classification); despite recognizable features – quadrangular stems, opposite leaves, and hypogynous flowers – that are nearly ubiquitous in the family, the only clear synapomorphy is a unique ovary anatomy. Nevertheless, since its expansion to include members of former Verbenaceae, Lamiaceae possess remarkable diversity, including expansive secondary chemistry, a cosmopolitan distribution, and a broad range of growth forms and life histories (e.g., ephemeral herbs [Pogogyne] to long-lived trees [Tectona]), floral architectures (e.g., actinomorphic to strongly bilabiate flowers, with 2-18 stamens), and ecological niche preferences (e.g., rainforest canopy dominants [Tectona], high alpine scree [Marmoritis], and desert halophytes [Saccocalyx]). Although Lamiaceae have a cosmopolitan distribution and are exceedingly species-rich, different subclades apparently experienced diversification under either similar or extraordinarily different sets of ecological conditions. Given these attributes, exploration and characterization of diversification patterns in Lamiaceae may contribute greatly to our general understanding of plant diversification and biogeography on a global scale.
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A. Callicarpa acuminata; B. Westringia cheelii; C. Symphorema involucratum; D. Vitex rotundifolia; E. Tectona grandis; F. Teucrium fruticans; G. Gmelina asiatica; H. Scutellaria sibthorpii; I. Galeopsis tetrahit