Biogeography of the cosmopolitan sedges (Cyperaceae) and the area‐richness correlation in plants

Abstract

Aim Across angiosperm families, the area occupied by a family is strongly correlated with its richness. We explore the causes of this area‐richness correlation using the cosmopolitan family, Cyperaceae Juss., as a model. We test the hypothesis that, despite a proposed tropical origin, temperate lineages in the family diversified at elevated rates. We test the hypothesis that the area‐richness correlation is maintained within intrafamilial clades, and that this relationship could be described as a function of niche space. We also test the hypothesis that the partitioning of geographical and ecological space, not the extent of this space, is the factor most closely associated with clade richness. Location Cosmopolitan. Methods We use molecular data from four genes sequenced in 384 taxa to develop a chronogram of Cyperaceae. We then develop a model of ancestral ranges and measure rates of diversification throughout the history of the family. Integrating data from over 4,800,000 digitized herbarium records, we characterize the range and niche of more than 4500 species and test for correlations of the species richness maintained within clades with range size, range partitioning, range overlap, niche, clade age and rate of diversification. Results Cyperaceae originated in South America in the late Cretaceous and subsequently dispersed throughout the globe. Of three increases in diversification rate, two occurred in the temperate Northern Hemisphere. The variable most closely associated with clade richness is the partitioning of geographical space by species within each clade. Main conclusions We show that species‐rich clades in Cyperaceae are not only more widespread, occupy more niche space, and diversify more quickly, but also exhibit patterns that are consistent with the partitioning of geographical and ecological space as a major correlate to diversification.

The spatial structure of phylogenetic and functional diversity in the United States and Canada: An example using the sedge family (Cyperaceae)

“…Missing species were generally evenly spread throughout the phylogeny, except for the genera Cyperus and Rhynchospora , which were missing 33% and 44.5% of species, respectively. The topology was largely consistent with both Spalink et al () and the Global Carex Group (), with incongruences limited to nodes that were weakly supported in either analysis.…”

“…The combined datasets from Spalink et al () and the Global Carex Group () contained a total of 697 species, or about 83% of all native Cyperaceae species of the USA and Canada (Figs., S2; Data S1). Missing species were generally evenly spread throughout the phylogeny, except for the genera Cyperus and Rhynchospora , which were missing 33% and 44.5% of species, respectively.…”

“…Previous analyses have demonstrated tropical Central and South America to be the “museum” of early Cyperaceae diversification (Spalink et al, ), with migrations of individual lineages into the northern hemisphere not occurring until the Eocene (∼55 mya), and the temperate radiation of Carex not occurring until the late Oligocene to early Miocene (∼25–20 mya) (Escudero & Hipp, ; Spalink et al, ). By these estimates, the invasion and diversification of Cyperaceae in the temperate north is a relatively recent phenomenon.…”

“…The ecological correlates of chromosome number variation in Carex remain a central issue in understanding how the genus Carex has accumulated over 2000 species in just over 20 million years (Spalink et al, ). Chromosome numbers in Carex are strongly linked to recombination rates (Burt, ), speciation rates (Chung et al, ; Escudero et al, ), gene flow rates (Hipp et al, ), and the fitness of species across landscapes (Bell, ; Escudero et al, , ).…”

A tale of worldwide success: Behind the scenes of Carex (Cyperaceae) biogeography and diversification

“…The origin and worldwide diversification of Carex have been discussed in relation to chromosome evolution and adaptation to colder climates (Escudero et al, ; Gebauer et al, ; Hoffmann et al, ), as well as fine‐scale partitioning of niche and distributional ranges of individual species within continents (Waterway et al, ; Gebauer et al, ; Pender, ; Spalink et al, 2016a, 2016b, ; Benítez‐Benítez et al, ). While Cyperaceae have been inferred to have arisen in South America at the late Cretaceous, it was the migration of the ancestors of Carex to the Northern Hemisphere that was the catalyst for the major diversification of this lineage (Léveillé‐Bourret et al, , , 2018a, 2018c; Spalink et al, ). Recent phylogenetic studies have discovered that several early‐diverged lineages of Carex and its closest living relatives are Southeast (SE) Asian (Starr & Ford, 2009; Waterway et al, ; Starr et al, ; Léveillé‐Bourret et al, 2018b), supporting the long‐held view that the genus originated in SE Asia (Nelmes, 1951; Raymond, 1955, 1959; Koyama, 1957; Ball, 1990).…”