Fossil palm reading: using fruits to reveal the deep roots of palm diversity

Abstract

Answering many fundamental questions in evolutionary biology requires information from fossils because they provide direct evidence of the diversity and geographic distributions of organisms through time. For studies of extant lineages, fossils cannot usually be incorporated without taxonomic or phylogenetic information. Unfortunately, well-sampled comparative morphological data sets are lacking for many plant clades, hindering the inclusion of fossils in many types of analyses. Comparative work in plant morphology and anatomy is therefore crucial for filling this gap and paving the way for more integrative research in plant macroevolution. We focus here on the Arecaceae (palms), which are a widespread tropical angiosperm family composed of approximately 2500 species organized into five subfamilies, 28 tribes, 27 subtribes, and 181 genera (Baker and Dransfield, 2016). They exhibit broad morphological and ecological diversity. Ranging in habit from acaulescent understory herbs to canopy trees and heavily armed lianas, today, palms occupy nearly all terrestrial environments of the tropics from rainforests to arid deserts. Palms have been prominent components of terrestrial environments for the last ~85 million years, during the Late Cretaceous and Cenozoic. Unequivocal macrofossils first appear in Coniacian strata of the Late Cretaceous (~90-86 Ma; Berry 1914, 1916) and become widespread by the Maastrichtian (~72-66 Ma), demonstrated by numerous occurrences of mangrove palms (subfamily Nypoideae;

Plastome structure, phylogenomic analyses and molecular dating of Arecaceae

“…We infer that the crown age of Arecaceae (96.60 Ma) was younger than that estimated by Janssen and Bremer (2004;110 Ma) (Janssen and Bremer, 2004;Couvreur et al, 2011;Baker and Couvreur, 2013;Mennes et al, 2015), this study selected two new suitable fossil node calibrations, and a secondary calibration point as the limit of the total root crown group time. Our findings were similar to those of most other studies, with the Arecaceae lineage originating in the Cretaceous and early Paleogene (Janssen and Bremer, 2004;Harley, 2006;Couvreur et al, 2011;Baker and Couvreur, 2013;Givnish et al, 2018;Matsunaga and Smith, 2021). The divergence times of subfamilies except Calamoideae were similar to the results of Couvreur et al, 2011;Baker and Couvreur (2013) (Nypoideae, stem, 93.5 Ma;Coryphoideae, stem, 86.6 Ma;Ceroxyloideae, stem, 78.2 Ma;Arecoideae, crown, 73.6 Ma).…”

X-ray microscopy enables multiscale high-resolution 3D imaging of plant cells, tissues, and organs

“…Alternatively, more rigid plant specimens can be contrasted in iodine and instead of agarose, stabilized with relatively X-ray transparent polyester fibers or small polystyrene beads, adding pieces of paper towel or lab wipes saturated with water or ethanol to maintain high relative humidity before sealing in sample tubes. Other robust plant materials such as wood samples ( Reynolds et al, 2018 ) or seeds and grains ( Su and Xiao, 2020 ; Han et al, 2021 ; Matsunaga and Smith, 2021 ) are readily imaged with XRM with a minimum of preparation. Supplemental Figure S8 shows XRM scans of maize, sorghum, soybean, and wheat seeds where no fixation or contrast enhancement were used.…”

Morphological reassessment of the movable calcar of delphacid planthoppers (Hemiptera: Fulgoromorpha: Delphacidae)

“…The Asiracinae Ugyopini recorded on dicotyledones mainly feed on woody dicots (most probably secondarily) and on monocotyledon Arecaceae. The family Arecaceae comprises 240 genera and approximately 2700 species predominantly concentrated in tropical and subtropical regions 105 , 106 , with fossil record reaching Late Cretaceous 107 . Type 2 calcar, as in Ugyopini, could be, on the one hand, a conservative model and, on the other, an expression of adaptation and a long co-evolutionary history with their host plants.…”