Chromosomal evolution, environmental heterogeneity, and migration drive spatial patterns of species richness in Calochortus (Liliaceae).

We used nuclear genomic data and statistical models to evaluate the ecological and evolutionary processes shaping spatial variation in species richness in Calochortus (Liliaceae, 74 spp.). Calochortus occupies diverse habitats in the western United States and Mexico and has a center of diversity in the California Floristic Province, marked by multiple orogenies, winter rainfall, and highly divergent climates and substrates (including serpentine). We used sequences of 294 low-copy nuclear loci to produce a time-calibrated phylogeny, estimate historical biogeography, and test hypotheses regarding drivers of present-day spatial patterns in species number. Speciation and species coexistence require reproductive isolation and ecological divergence, so we examined the roles of chromosome number, environmental heterogeneity, and migration in shaping local species richness. Six major clades-inhabiting different geographic/climatic areas, and often marked by different base chromosome numbers (n = 6 to 10)-began diverging from each other ~10.3 Mya. As predicted, local species number increased significantly with local heterogeneity in chromosome number, elevation, soil characteristics, and serpentine presence. Species richness is greatest in the Transverse/Peninsular Ranges where clades with different chromosome numbers overlap, topographic complexity provides diverse conditions over short distances, and several physiographic provinces meet allowing immigration by several clades. Recently diverged sister-species pairs generally have peri-patric distributions, and maximum geographic overlap between species increases over the first million years since divergence, suggesting that chromosomal evolution, genetic divergence leading to gametic isolation or hybrid inviability/sterility, and/or ecological divergence over small spatial scales may permit species co-occurrence.

Ecophysiological adaptations shape distributions of closely related trees along a climatic moisture gradient.

Tradeoffs between the energetic benefits and costs of traits can shape species and trait distributions along environmental gradients. Here we test predictions based on such tradeoffs using survival, growth, and 50 photosynthetic, hydraulic, and allocational traits of ten Eucalyptus species grown in four common gardens along an 8-fold gradient in precipitation/pan evaporation (P/Ep) in Victoria, Australia. Phylogenetically structured tests show that most trait-environment relationships accord qualitatively with theory. Most traits appear adaptive across species within gardens (indicating fixed genetic differences) and within species across gardens (indicating plasticity). However, species from moister climates have lower stomatal conductance than others grown under the same conditions. Responses in stomatal conductance and five related traits appear to reflect greater mesophyll photosynthetic sensitivity of mesic species to lower leaf water potential. Our data support adaptive cross-over, with realized height growth of most species exceeding that of others in climates they dominate. Our findings show that pervasive physiological, hydraulic, and allocational adaptations shape the distributions of dominant Eucalyptus species along a subcontinental climatic moisture gradient, driven by rapid divergence in species P/Ep and associated adaptations.

Plant biology: Phylogenomics of mustards and their relatives.

A new nuclear phylogeny for the large family Brassicaceae opens the way for advanced comparative studies of adaptation, development, coevolution, hybridization, and diversification in this crucial group, which is the source for many of the genomic resources now used across the flowering plants.

Phylotranscriptomic Analyses of Mycoheterotrophic Monocots Show a Continuum of Convergent Evolutionary Changes in Expressed Nuclear Genes From Three Independent Nonphotosynthetic Lineages.

Mycoheterotrophy is an alternative nutritional strategy whereby plants obtain sugars and other nutrients from soil fungi. Mycoheterotrophy and associated loss of photosynthesis have evolved repeatedly in plants, particularly in monocots. Although reductive evolution of plastomes in mycoheterotrophs is well documented, the dynamics of nuclear genome evolution remains largely unknown. Transcriptome datasets were generated from four mycoheterotrophs in three families (Orchidaceae, Burmanniaceae, Triuridaceae) and related green plants and used for phylogenomic analyses to resolve relationships among the mycoheterotrophs, their relatives, and representatives across the monocots. Phylogenetic trees based on 602 genes were mostly congruent with plastome phylogenies, except for an Asparagales + Liliales clade inferred in the nuclear trees. Reduction and loss of chlorophyll synthesis and photosynthetic gene expression and relaxation of purifying selection on retained genes were progressive, with greater loss in older nonphotosynthetic lineages. One hundred seventy-four of 1375 plant benchmark universally conserved orthologous genes were undetected in any mycoheterotroph transcriptome or the genome of the mycoheterotrophic orchid Gastrodia but were expressed in green relatives, providing evidence for massively convergent gene loss in nonphotosynthetic lineages. We designate this set of deleted or undetected genes Missing in Mycoheterotrophs (MIM). MIM genes encode not only mainly photosynthetic or plastid membrane proteins but also a diverse set of plastid processes, genes of unknown function, mitochondrial, and cellular processes. Transcription of a photosystem II gene (psb29) in all lineages implies a nonphotosynthetic function for this and other genes retained in mycoheterotrophs. Nonphotosynthetic plants enable novel insights into gene function as well as gene expression shifts, gene loss, and convergence in nuclear genomes.

Phylogenomic resolution of order- and family-level monocot relationships using 602 single-copy nuclear genes and 1375 BUSCO genes.

We assess relationships among 192 species in all 12 monocot orders and 72 of 77 families, using 602 conserved single-copy (CSC) genes and 1375 benchmarking single-copy ortholog (BUSCO) genes extracted from genomic and transcriptomic datasets. Phylogenomic inferences based on these data, using both coalescent-based and supermatrix analyses, are largely congruent with the most comprehensive plastome-based analysis, and nuclear-gene phylogenomic analyses with less comprehensive taxon sampling. The strongest discordance between the plastome and nuclear gene analyses is the monophyly of a clade comprising Asparagales and Liliales in our nuclear gene analyses, versus the placement of Asparagales and Liliales as successive sister clades to the commelinids in the plastome tree. Within orders, around six of 72 families shifted positions relative to the recent plastome analysis, but four of these involve poorly supported inferred relationships in the plastome-based tree. In Poales, the nuclear data place a clade comprising Ecdeiocoleaceae+Joinvilleaceae as sister to the grasses (Poaceae); Typhaceae, (rather than Bromeliaceae) are resolved as sister to all other Poales. In Commelinales, nuclear data place Philydraceae sister to all other families rather than to a clade comprising Haemodoraceae+Pontederiaceae as seen in the plastome tree. In Liliales, nuclear data place Liliaceae sister to Smilacaceae, and Melanthiaceae are placed sister to all other Liliales except Campynemataceae. Finally, in Alismatales, nuclear data strongly place Tofieldiaceae, rather than Araceae, as sister to all the other families, providing an alternative resolution of what has been the most problematic node to resolve using plastid data, outside of those involving achlorophyllous mycoheterotrophs. As seen in numerous prior studies, the placement of orders Acorales and Alismatales as successive sister lineages to all other extant monocots. Only 21.2% of BUSCO genes were demonstrably single-copy, yet phylogenomic inferences based on BUSCO and CSC genes did not differ, and overall functional annotations of the two sets were very similar. Our analyses also reveal significant gene tree-species tree discordance despite high support values, as expected given incomplete lineage sorting (ILS) related to rapid diversification. Our study advances understanding of monocot relationships and the robustness of phylogenetic inferences based on large numbers of nuclear single-copy genes that can be obtained from transcriptomes and genomes.

Functional traits mediate individualistic species-environment distributions at broad spatial scales while fine-scale species associations remain unpredictable.

PREMISE: Numerous processes influence plant distributions and co-occurrence patterns, including ecological sorting, limiting similarity, and stochastic effects. To discriminate among these processes and determine the spatial scales at which they operate, we investigated how functional traits and phylogenetic relatedness influence the distribution of temperate forest herbs. METHODS: We surveyed understory plant communities across 257 forest stands in Wisconsin and Michigan (USA) and applied Bayesian phylogenetic linear mixed-effects models (PGLMMs) to quantify how functional traits and phylogenetic relatedness influence the environmental distribution of 139 herbaceous plant species along broad edaphic, climatic, and light gradients. These models also allowed us to test how functional and phylogenetic similarity affect species co-occurrence within microsites. RESULTS: Leaf height, specific leaf area, and seed mass all influenced individualistic plant distributions along landscape-scale gradients in soil texture, soil fertility, light availability, and climate. In contrast, phylogenetic relationships did not consistently predict species-environment relationships. Neither functionally similar nor phylogenetically related herbs segregated among microsites within forest stands. CONCLUSIONS: Trait-mediated ecological sorting appears to drive temperate-forest community assembly, generating individualistic plant distributions along regional environmental gradients. This finding links classic studies in plant ecology and prior research in plant physiological ecology to current trait-based approaches in community ecology. However, our results fail to support the common assumption that limiting similarity governs local plant co-occurrences. Strong ecological sorting among forest stands coupled with stochastic fine-scale interactions among species appear to weaken deterministic, niche-based assembly processes at local scales.

Leaf NPK stoichiometry, δ15 N, and apparent nutrient limitation of co-occurring carnivorous and noncarnivorous plants.

Previous meta-analyses suggested that carnivorous plants-despite access to N, P, and K from prey-have significantly lower leaf concentrations of these nutrients than noncarnivores. Those studies, however, largely compared carnivores in nutrient-poor habitats with noncarnivores in more nutrient-rich sites, so that the differences reported might reflect habitat differences as much as differences in nutrient-capture strategy. Here we examine three carnivorous and 12 noncarnivorous plants in the same nutrient-poor bog to compare their foliar nutrient concentrations, assess their patterns of nutrient limitation using leaf NPK stoichiometry, and estimate percentage N derived from prey by carnivores using a mixing model for stable N isotopes. We hypothesized that (1) carnivore leaf nutrient concentrations approach or exceed those of noncarnivores in the same nutrient-poor habitat; (2) species in different functional groups show different patterns of stoichiometry and apparent nutrient limitation; and (3) noncarnivores might show evidence of using other means of nutrient acquisition or conservation to reduce nutrient limitation. At Fallison Bog in northern Wisconsin, carnivorous plants (Drosera rotundifolia, Sarracenia purpurea, Utricularia macrorhiza) showed significantly lower leaf percentage C and N:P ratio, higher δ15 N, and no difference from noncarnivores in leaf N, P, K, and δ13 C. Sedges had significantly lower leaf percentage P, percentage C, and N:K ratio, and higher K:P ratio than nonsedges restricted to the Sphagnum mat, and may tap peat N via aerenchyma-facilitated peat oxidation (oxipeditrophy). Evergreen ericaceous shrubs exhibited significantly higher levels of percentage C and lower values of δ15 N than mat nonericads. Calla palustris-growing in the nutrient-rich moat at the bog's upland edge-had very high values of leaf N, K, δ15 N, and N:P ratio, suggesting that it may obtain nutrients from minerotrophic flows from the adjacent uplands and/or rapidly decaying peat. Stoichiometric analyses indicated that most species are N limited. A mixing model applied to δ15 N values for carnivores, noncarnivores, and insects produced an estimate of 50% of leaf N derived from prey for Utricularia, 42% for Sarracenia, and 41% for Drosera.

Hydroscapes, hydroscape plasticity and relationships to functional traits and mesophyll photosynthetic sensitivity to leaf water potential in Eucalyptus species.

The isohydric-anisohydric continuum describes the relative stringency of stomatal control of leaf water potential (ψleaf ) during drought. Hydroscape area (HA)-the water potential landscape over which stomata regulate ψleaf -has emerged as a useful metric of the iso/anisohydric continuum because it is strongly linked to several hydraulic, photosynthetic and structural traits. Previous research on HA focused on broad ecological patterns involving several plant clades. Here we investigate the relationships between HA and climatic conditions and functional traits across ecologically diverse but closely related species while accounting for phylogeny. Across a macroclimatic moisture gradient, defined by the ratio of mean annual precipitation to mean annual pan evaporation (P/Ep ), HA decreased with increased P/Ep across 10 Eucalyptus species. Greater anisohydry reflects lower turgor loss points and greater hydraulic safety, mirroring global patterns. Larger HA coincides with mesophyll photosynthetic capacity that is more sensitive to ψleaf . Hydroscapes exhibit little plasticity in response to variation in water supply, and the extent of plasticity does not vary with P/Ep of native habitats. These findings strengthen the case that HA is a useful metric for characterizing drought tolerance and water-status regulation.

A new carnivorous plant lineage (Triantha) with a unique sticky-inflorescence trap.

Carnivorous plants consume animals for mineral nutrients that enhance growth and reproduction in nutrient-poor environments. Here, we report that Triantha occidentalis (Tofieldiaceae) represents a previously overlooked carnivorous lineage that captures insects on sticky inflorescences. Field experiments, isotopic data, and mixing models demonstrate significant N transfer from prey to Triantha, with an estimated 64% of leaf N obtained from prey capture in previous years, comparable to levels inferred for the cooccurring round-leaved sundew, a recognized carnivore. N obtained via carnivory is exported from the inflorescence and developing fruits and may ultimately be transferred to next year's leaves. Glandular hairs on flowering stems secrete phosphatase, as seen in all carnivorous plants that directly digest prey. Triantha is unique among carnivorous plants in capturing prey solely with sticky traps adjacent to its flowers, contrary to theory. However, its glandular hairs capture only small insects, unlike the large bees and butterflies that act as pollinators, which may minimize the conflict between carnivory and pollination.

Mesophyll photosynthetic sensitivity to leaf water potential in Eucalyptus: a new dimension of plant adaptation to native moisture supply.

Photosynthetic sensitivity to drought is a fundamental constraint on land-plant evolution and ecosystem function. However, little is known about how the sensitivity of photosynthesis to nonstomatal limitations varies among species in the context of phylogenetic relationships. Using saplings of 10 Eucalyptus species, we measured maximum CO2 -saturated photosynthesis using A-ci curves at several different leaf water potentials (ψleaf ) to quantify mesophyll photosynthetic sensitivity to ψleaf (MPS), a measure of how rapidly nonstomatal limitations to carbon uptake increase with declining ψleaf . MPS was compared to the macroclimatic moisture availability of the species' native habitats, while accounting for phylogenetic relationships. We found that species native to mesic habitats have greater MPS but higher maximum photosynthetic rates during non-water-stressed conditions, revealing a trade-off between maximum photosynthesis and drought sensitivity. Species with lower turgor loss points have lower MPS, indicating coordination among photosynthetic and water-relations traits. By accounting for phylogenetic relationships among closely related species, we provide the first compelling evidence that MPS in Eucalyptus evolved in an adaptive fashion with climatically determined moisture availability, opening the way for further study of this poorly explored dimension of plant adaptation to drought.

Mistletoes and their eucalypt hosts differ in the response of leaf functional traits to climatic moisture supply.

Trade-offs between photosynthesis and the costs of resource capture inform economic strategies of plants across environmental gradients and result in predictable variation in leaf traits. However, understudied functional groups like hemiparasites that involve dramatically different strategies for resource capture may have traits that deviate from expectations. We measured leaf traits related to gas exchange in mistletoes and their eucalypt hosts along a climatic gradient in relative moisture supply, measured as the ratio of precipitation to pan evaporation (P/Ep), in Victoria, Australia. We compared traits for mistletoes vs. hosts as functions of relative moisture supply and examined trait-trait correlations in both groups. Eucalypt leaf traits responded strongly to decreasing P/Ep, consistent with economic theory. Leaf area and specific leaf area (SLA) decreased along the P/Ep gradient, while C:N ratio, leaf thickness, N per area, and δ13C all increased. Mistletoes responded overall less strongly to P/Ep based on multivariate analyses; individual traits sometimes shifted in parallel with those of hosts, but SLA, leaf thickness, and N per area showed no significant change across the gradient. For mistletoes, leaf thickness was inversely related to leaf dry matter content (LDMC), with no relationship between SLA and mass-based N. In mistletoes, reduced costs of transpiration (reflecting their lack of roots) and abundant succulent leaf tissue help account for observed differences from their eucalypt hosts. Trait-based analysis of atypical functional types such as mistletoes help refine hypotheses based on plant economics and specialized adaptations to resource limitation.

Fine-scale environmental heterogeneity and spatial niche partitioning among spring-flowering forest herbs.

PREMISE: Environmental heterogeneity influences plant distributions and diversity at several spatial scales. In temperate forests, fine-scale environmental variation may promote local coexistence among herbaceous species by allowing plants to spatially partition microsites within forest stands. Here we argue that shallow soils, low soil water-holding capacity and fertility, and reduced light near tree boles should favor short, shallow-rooted, evergreen species like Anemone acutiloba with low moisture, nutrient, and light requirements. Farther from trees, richer, deeper soils should favor taller, deeper-rooted herbs with greater moisture and nutrient demands, such as Sanguinaria canadensis and Trillium flexipes. METHODS: We tested these hypotheses by mapping the fine-scale distributions of Anemone, Sanguinaria, and Trillium individuals within a 50 × 50 m plot, comparing local species' distributions with respect to soil depth and proximity to neighboring trees, and characterizing intraspecific and interspecific spatial associations. RESULTS: Local plant distributions were consistent with our predictions based on leaf height, physiology, and phenology. Anemone was found in microsites on shallower soils and closer to trees than either Sanguinaria or Trillium. In all three species, individual plants were spatially aggregated within 2 m, but spatially segregated from individuals of the other species beyond 2 m. CONCLUSIONS: Differential plant responses to fine-scale environmental heterogeneity and observed spatial associations suggest that local species-environment associations could facilitate coexistence. These findings illustrate how fine-scale environmental heterogeneity coupled with phenological and physiological differences likely contribute to spatial niche partitioning among spring-flowering forest herbs and maintain high local plant diversity within temperate forests.

Adaptive associations among life history, reproductive traits, environment, and origin in the Wisconsin angiosperm flora.

PREMISE: We tested 25 classic and novel hypotheses regarding trait-origin, trait-trait, and trait-environment relationships to account for flora-wide variation in life history, habit, and especially reproductive traits using a plastid DNA phylogeny of most native (96.6%, or 1494/1547 species) and introduced (87.5%, or 690/789 species) angiosperms in Wisconsin, USA. METHODS: We assembled data on life history, habit, flowering, dispersal, mating system, and occurrence across open/closed/mixed habitats across species in the state phylogeny. We used phylogenetically structured analyses to assess the strength and statistical significance of associations predicted by our models. RESULTS: Introduced species are more likely to be annual herbs, occupy open habitats, have large, visually conspicuous, hermaphroditic flowers, and bear passively dispersed seeds. Among native species, hermaphroditism is associated with larger, more conspicuous flowers; monoecy is associated with small, inconspicuous flowers and passive seed dispersal; and dioecy is associated with small, inconspicuous flowers and fleshy fruits. Larger flowers with more conspicuous colors are more common in open habitats, and in understory species flowering under open (spring) canopies; fleshy fruits are more common in closed habitats. Wind pollination may help favor dioecy in open habitats. CONCLUSIONS: These findings support predictions regarding how breeding systems depend on flower size, flower color, and fruit type, and how those traits depend on habitat. This study is the first to combine flora-wide phylogenies with complete trait databases and phylogenetically structured analyses to provide powerful tests of evolutionary hypotheses about reproductive traits and their variation with geographic source, each other, and environmental conditions.

The Adaptive Geometry of Trees Revisited.

The Adaptive Geometry of Trees had an important conceptual influence on plant ecology and helped inspire many new approaches to understanding succession, plant adaptation, and plant competition. Its central model provided an elegant potential explanation for how optimal canopy form should shift with ecological conditions, change those conditions through time, and thus help drive succession and be a consequence of it. Yet on close examination, this deeply inspirational model does not lead to the predictions for which it is widely known. Here I show that the Horn model actually favors monolayer canopies over multilayers under all light conditions if relative growth rate (growth per unit investment) is maximized. Horn's conclusion that multilayers would be favored over monolayers in brighter sites is an artifact. I propose that self-shading multilayers might gain an advantage in brightly lit sites by reducing water loss, reducing the costs of branch construction and maintenance, reducing photoinhibition, increasing light capture in sidelit microsites, and increasing water and nutrient supplies (or leaf longevity) when combined with one or more of the previous potential advantages. I conclude with a brief discussion connecting Horn's model to other conceptual frameworks in plant ecology and outlining possible future extensions.

Plant distribution, stature, rarity, and diversity in a patterned calcareous fen: tests of geochemical and leaf-height models.

PREMISE: In patterned fens, patches of short, sparse, species-rich vegetation often occur on substrates rich in precipitated carbonates near calcareous springheads, with taller, denser vegetation farther away. Boyer and Wheeler (1989) hypothesized that phosphorus co-precipitation near springheads limits plant productivity and coverage, and Givnish (1982) proposed that aggregations of rare, short-statured plant species might reflect their competitive restriction to sparsely covered microsites. METHODS: We tested these hypotheses by quantifying species distributions, leaf heights, plant coverage, community composition, and substrate and leaf chemistry of Eupatorium perfoliatum along a gradient of hydrology and geochemistry in a wetland complex in southeastern Wisconsin, USA, ranging from marl flats and fens on peat mounds near springheads to surrounding sedge meadows. RESULTS: Community composition was strongly correlated with a one-dimensional environmental gradient along which coverage and height increased moving downslope from marl flats, while soil carbonate, phosphorus immobilization capacity, and local species richness decreased, consistent with theory. Regionally rare species were short and restricted to sparsely covered microsites; within and among species, leaf height increased with local coverage. NPK tissue stoichiometry did not entirely support the Boyer-Wheeler hypothesis, although nitrogen limitation appeared strongest in sedge meadows. Shifts in stature and tissue chemistry of E. perfoliatum along the marl flat-sedge meadow gradient suggested that zinc toxicity may help limit coverage near springheads despite no significant change in soil zinc content. CONCLUSIONS: We propose a modified Boyer-Wheeler hypothesis to account for cascading effects of phosphorus co-precipitation near springheads on nitrogen fixation, nitrogen+phosphorus co-limitation, and zinc mobility.

Spatial phylogenetics reveals evolutionary constraints on the assembly of a large regional flora.

PREMISE OF THE STUDY: We used spatial phylogenetics to analyze the assembly of the Wisconsin flora, linking processes of dispersal and niche evolution to spatial patterns of floristic and phylogenetic diversity and testing whether phylogenetic niche conservatism can account for these patterns. METHODS: We used digitized records and a new molecular phylogeny for 93% of vascular plants in Wisconsin to estimate spatial variation in species richness and phylogenetic α and ß diversity in a native flora shaped mainly by postglacial dispersal and response to environmental gradients. We developed distribution models for all species and used these to infer fine-scale variation in potential diversity, phylogenetic distance, and interspecific range overlaps. We identified 11 bioregions based on floristic composition, mapped areas of neo- and paleo-endemism to establish new conservation priorities and predict how community-assembly patterns should shift with climatic change. KEY RESULTS: Spatial phylogenetic turnover most strongly reflects differences in temperature and spatial distance. For all vascular plants, assemblages shift from phylogenetically clustered to overdispersed northward, contrary to most other studies. This pattern is lost for angiosperms alone, illustrating the importance of phylogenetic scale. CONCLUSIONS: Species ranges and assemblage composition appear driven primarily by phylogenetic niche conservatism. Closely related species are ecologically similar and occupy similar territories. The average level and geographic structure of plant phylogenetic diversity within Wisconsin are expected to greatly decline over the next half century, while potential species richness will increase throughout the state. Our methods can be applied to allochthonous communities throughout the world.

Monocot plastid phylogenomics, timeline, net rates of species diversification, the power of multi-gene analyses, and a functional model for the origin of monocots.

PREMISE OF THE STUDY: We present the first plastome phylogeny encompassing all 77 monocot families, estimate branch support, and infer monocot-wide divergence times and rates of species diversification. METHODS: We conducted maximum likelihood analyses of phylogeny and BAMM studies of diversification rates based on 77 plastid genes across 545 monocots and 22 outgroups. We quantified how branch support and ascertainment vary with gene number, branch length, and branch depth. KEY RESULTS: Phylogenomic analyses shift the placement of 16 families in relation to earlier studies based on four plastid genes, add seven families, date the divergence between monocots and eudicots+Ceratophyllum at 136 Mya, successfully place all mycoheterotrophic taxa examined, and support recognizing Taccaceae and Thismiaceae as separate families and Arecales and Dasypogonales as separate orders. Only 45% of interfamilial divergences occurred after the Cretaceous. Net species diversification underwent four large-scale accelerations in PACMAD-BOP Poaceae, Asparagales sister to Doryanthaceae, Orchidoideae-Epidendroideae, and Araceae sister to Lemnoideae, each associated with specific ecological/morphological shifts. Branch ascertainment and support across monocots increase with gene number and branch length, and decrease with relative branch depth. Analysis of entire plastomes in Zingiberales quantifies the importance of non-coding regions in identifying and supporting short, deep branches. CONCLUSIONS: We provide the first resolved, well-supported monocot phylogeny and timeline spanning all families, and quantify the significant contribution of plastome-scale data to resolving short, deep branches. We outline a new functional model for the evolution of monocots and their diagnostic morphological traits from submersed aquatic ancestors, supported by convergent evolution of many of these traits in aquatic Hydatellaceae (Nymphaeales).