Evolutionary origins of the eastern North American–Mesoamerican floristic disjunction: Current status and future prospects

Abstract

Biogeographic disjunction patterns, where multiple taxa are shared between isolated geographic areas, represent excellent systems for investigating the historical assembly of modern biotas and fundamental biological processes such as speciation, diversification, niche evolution, and evolutionary responses to climate change. Studies on plant genera disjunct across the northern hemisphere, particularly between eastern North America (ENA) and eastern Asia (EAS), have yielded tremendous insight on the geologic history and assembly of rich temperate floras. However, one of the most prevalent disjunction patterns involving ENA forests has been largely overlooked: that of taxa disjunct between ENA and cloud forests of Mesoamerica (MAM), with examples including Acer saccharum, Liquidambar styraciflua, Cercis canadensis, Fagus grandifolia, and Epifagus virginiana. Despite the remarkable nature of this disjunction pattern, which has been recognized for over 75 years, there have been few recent efforts to empirically examine its evolutionary and ecological origins. Here I synthesize previous systematic, paleobotanical, phylogenetic, and phylogeographic studies to establish what is known about this disjunction pattern to provide a roadmap for future research. I argue that this disjunction pattern, and the evolution and fossil record of the Mexican flora more broadly, represents a key missing piece in the broader puzzle of northern hemisphere biogeography. I also suggest that the ENA–MAM disjunction represents an excellent system for examining fundamental questions about how traits and life history strategies mediate plant evolutionary responses to climate change and for predicting how broadleaf temperate forests will respond to the ongoing climatic pressures of the Anthropocene.

Pliocene seeds of Passiflora subgenus Decaloba (Gray Fossil Site, Tennessee) and the impact of the fossil record on understanding the diversification and biogeography of Passiflora

“…Most species in section Decaloba s.s. are Neotropical (Acha et al, 2021), with the Bahamas, northern Mexico, and the southern portions of Arizona and Texas making up the northernmost extension of the section's modern native range (Killip, 1938; MacDougal, 2001b; Kay, 2003; Goldman, 2004; Ulmer and MacDougal, 2004; MacDougal, 2011; Goldman and MacDougal, 2015; Villaseñor, 2016). It is possible that P. sulcatasperma fits an eastern North America–eastern Mexico disjunct biogeographic pattern, where related taxa (species, genera, or infrageneric clades) occur in the modern eastern North American flora and the flora of eastern Mexico and Guatemala, sometimes also ranging into Central and South America (Miranda and Sharp, 1950; Dressler, 1954; Graham, 1999, 2010; Manos and Meireles, 2015; Stull, 2023 [accepted author manuscript]). Many of these taxa are thought to have reached Mexico by dispersing or shifting their ranges southward in the Miocene or later (Miranda and Sharp, 1950; Dressler, 1954; Graham, 1999, 2010; Manos and Meireles, 2015; Stull, 2023 [accepted author manuscript]).…”

“…It is possible that P. sulcatasperma fits an eastern North America–eastern Mexico disjunct biogeographic pattern, where related taxa (species, genera, or infrageneric clades) occur in the modern eastern North American flora and the flora of eastern Mexico and Guatemala, sometimes also ranging into Central and South America (Miranda and Sharp, 1950; Dressler, 1954; Graham, 1999, 2010; Manos and Meireles, 2015; Stull, 2023 [accepted author manuscript]). Many of these taxa are thought to have reached Mexico by dispersing or shifting their ranges southward in the Miocene or later (Miranda and Sharp, 1950; Dressler, 1954; Graham, 1999, 2010; Manos and Meireles, 2015; Stull, 2023 [accepted author manuscript]). Neotropical clades have also more rarely dispersed or shifted their ranges northward into eastern North America (Manos and Meireles, 2015).…”

Variación morfológica foliar de Brickellia sección Barroetea (A. Gray) E.E. Schill. & R. Scott y especies afines

“…la magnitud de cambio morfológico del linaje C, sea la respuesta a la presión ambiental ocasionada por los eventos de sequía durante su diversificación en el Mioceno (Ramírez-Arriaga et al 2014, Stull 2023; la mayoría de las especies actuales del linaje prosperan en zonas áridas o semiáridas, mientras que las especies del linaje D (excepto Kuhnia) se distribuyen en zonas templadas o tropicales, ambientes al parecer menos estresantes para la mayoría de las plantas (Stebbins 1952). Los resultados apoyan la hipótesis de una migración de Brickellia hacia el sur, siguiendo el enfriamiento de las temperaturas después del Mioceno (Stull 2023).…”