Phylogenetic tree of vascular plants reveals the origins of aquatic angiosperms

Abstract

Although aquatic plants are discussed as a unified biological group, they are phylogenetically well dispersed across the angiosperms. In this study, we annotated the aquatic taxa on the tree of vascular plants, and extracted the topology of these aquatic lineages to construct the tree of aquatic angiosperms. We also reconstructed the ancestral areas of aquatic families. We found that aquatic angiosperms could be divided into two different categories: the four aquatic orders and the aquatic taxa in terrestrial orders. Aquatic lineages evolved early in the radiation of angiosperms, both in the orders Nymphaeales and Ceratophyllales and among basal monocots (Acorales and Alismatales). These aquatic orders do not have any extant terrestrial relatives. They originated from aquatic habitats during the Early Cretaceous. Asia would have been one of the centers for early diversification of aquatic angiosperms. The aquatic families within terrestrial orders may originate from other areas besides Asia, such as America or Australia. The lineages leading to extant angiosperms diversified early in underexploited freshwater habitats. The four extant aquatic orders were relicts of an early radiation of angiosperm in aquatic environments. Their extinct ancestors might be aquatic early angiosperms.Key words: ancestral area, aquatic plant, early angiosperm, fossil age, origin.Amborella, Nymphaeales, and Austrobaileyales represent the three earliest splits in angiosperm phylogeny (ANA grade angiosperms), followed by the five lineages of mesangiosperms, Magnoliids, Chloranthales, monocots, Ceratophyllales, and eudicots (Cantino et al., 2007;Soltis et al., 2008). The rapid diversification of angiosperms in the Early Cretaceous is well documented in the fossil record (Feild & Arens, 2005). Due to the diversity of fossils, it is impossible to draw unequivocal conclusions on the life form of early angiosperms (L€ ohne, 2006). There are two divergent views on the general habit of the earliest angiosperms: woody and terrestrial or herbaceous and aquatic . The hypothesis that the earliest angiosperms were woody is supported by the evidence that most basal angiosperms are woody and all gymnosperms are woody ).An aquatic origin of angiosperms is supported by the evidence that several of the earliest known fossil angiosperms were aquatic. Archaefructus represents one of the oldest, most complete angiosperm fossils (Sun et al., 2002). It is estimated to be approximately 125 million years old, and on the basis of morphology, it clearly was aquatic. The phylogenetic placement of Archaefructus as sister to all extant angiosperms (Sun et al., 2002), and the near-basal phylogenetic position of Nymphaeales, support the hypothesis that the aquatic habit arose early in angiosperms and the earliest angiosperms might be aquatic (Coiffard et al., 2007;Soltis et al., 2008).Aquatic plants are plants that have adapted to live in aquatic environments (freshwater or saltwater). These plants require special adaptations for living submerged in water, o...

Herbivorous dinosaur jaw disparity and its relationship to extrinsic evolutionary drivers

“…Disparity (dots) is plotted alongside jaw specimen sample size curve (diamonds). Flower represents earliest fossil angiosperms (Sun et al 2002 ; Du and Wang 2015 ). …”

Convergent Loss of an EDS1/PAD4 Signaling Pathway in Several Plant Lineages Reveals Coevolved Components of Plant Immunity and Drought Response

“…There are, however, several species such as sacred lotus (Nelumbo nucifera) and O. sativa that, according to our analysis, have retained EDS1/PAD4 and other signaling pathway members despite inhabiting water-saturated environments. Furthermore, controversy surrounds the question of whether the most recent common ancestor of monocots could have had an aquatic lifestyle (Du et al, 2016;Givnish et al, 2018). It is nevertheless tempting to speculate that loss of the RNL and EDS1 pathway can be a byproduct of the physiological changes and differing environmental selection pressures associated with each lifestyle.…”

Relationships between key functional traits of the waterlily Nuphar lutea and wetland nutrient content

“…Among aquatic plants, species of Nymphaeaceae are singular because of their basal and partly non-elucidated position in angiosperm phylogeny (Padgett, Les & Crow, 1999; Du & Wang, 2016) and their very ancient occurrence in the fossil register (Du & Wang, 2016). Their rather unique and very large size among strictly aquatic plants and their dominance in quite monospecific stands in undisturbed ecosystems (Bornette et al, 2008) make them a major contributor to aquatic plant biomass (considering both above and belowground biomass) and turn-over (Brock, Van Der Velde & Van de Steeg, 1987).…”