Form, function and environments of the early angiosperms: merging extant phylogeny and ecophysiology with fossils

Abstract

Contents Summary 1 Introduction 2 Previous images of early angiosperms and their habitats 3 Progress in understanding angiosperm phylogeny: extant ‘basal’ relations 4 Early angiosperm ecology: inferences from extant plants and reflections from the fossil record 5 The ecology of angiosperm diversification: gaining a roothold and subsequent diversification 15 The environmental context of early angiosperm evolution 17 Conclusions 20 Acknowledgements 20 References 20 Summary The flowering plants – angiosperms – appeared during the Early Cretaceous period and within 10–30 Myr dominated the species composition of many floras worldwide. Emerging insights into the phylogenetics of development and discoveries of early angiosperm fossils are shedding increased light on the patterns and processes of early angiosperm evolution. However, we also need to integrate ecology, in particular how early angiosperms established a roothold in pre‐existing Mesozoic plant communities. These events were critical in guiding subsequent waves of angiosperm diversification during the Aptian–Albian. Previous pictures of the early flowering plant ecology have been diverse, ranging from large tropical rainforest trees, weedy drought‐adapted and colonizing shrubs, disturbance‐ and sun‐loving rhizomatous herbs, and, more recently, aquatic herbs; however, none of these images were tethered to a robust hypothesis of angiosperm phylogeny. Here, we synthesize our current understanding of early angiosperm ecology, focusing on patterns of functional ecology, by merging recent molecular phylogenetic studies and functional studies on extant ‘basal angiosperms’ with the picture of early angiosperm evolution drawn by the fossil record.

Stem Anatomy and the Evolution of Woodiness in Piperales

“…This topology is suggested to support the idea that early-diverging lineages of angiosperms possessed an active bifacial cambium Feild and Arens 2005;Spicer and Groover 2010). Because of its phylogenetic position and its diversity of growth forms, Piperales has been considered as a key lineage for understanding the early diversification of angiosperms (Carlquist 2009;Isnard et al 2012).…”

Fire and the Angiosperm Revolutions

“…More frequent fires, in turn, would promote low-biomass vegetation at the expense of trees and slow-growing gymnosperms. The initial spread of angiosperms from their putative dark, damp, and disturbed understory habit (Feild and Arens 2005) to their dominance in sunlit open habitats would have been caused by the appearance of this novel flowering plant-fire cycle, according to Bond and Scott (2010). The fossil evidence suggests that angiosperms began to dominate low-to midlatitude ecosystems only by the mid-Cretaceous (Wing and Boucher 1998;Lupia et al 1999;McElwain et al 2005).…”

“…Analogous patterns probably developed in the Cretaceous in warmer low and midlatitudes, where the vegetation came to be dominated by angiosperm herbs, shrubs, and small trees that replaced gymnosperm forests. Although early angiosperms may have grown in dark, damp, understory habitats (Feild and Arens 2005;Feild et al 2009), there is considerable fossil evidence that they evolved into sun-loving, low-statured, ''weedy'' plants during the period of major expansion from the mid-to late Cretaceous (100-70 Ma; Taylor and Hickey 1996;Wing and Boucher 1998;Brodribb and Feild 2010;Royer et al 2010). Early Cretaceous angiosperm fossils often occur on disturbed alluvial sites, where flooding would have helped maintain open, disturbed habitats (Hickey and Doyle 1977).…”

“…Several studies have shown that trees on stable forest margins differ from those in the forest interior in having thicker bark and the capacity to resprout after they are burned (Hoffmann et al 2009;VanderWeide and Hartnett 2011). The ability of woody angiosperms to resprout after major disturbance may be basal to angiosperms (Feild and Arens 2005). Most conifers cannot resprout, or resprouting is derived (Agee 1998;Keeley and Zedler 1998;Bond and Midgley 2003).…”

Trait Evolution, Community Assembly, and the Phylogenetic Structure of Ecological Communities

“…This has implications for the analysis of communities in which taxa are derived from disparate ancestral environmental conditions or for communities assembled in novel or extreme environments (Ackerly 2003). For example, among angiosperms, at a global scale, temperate and boreal communities may appear more clustered than tropical communities if frost tolerance is a recently derived trait in formerly tropical lineages (Wiens and Donoghue 2004;Feild and Arens 2005).…”