Topic
Trithuria
About: Trithuria is a research topic. Over the lifetime, 30 publications have been published within this topic receiving 1046 citations.
Papers
TL;DR: It is shown that Hydatellaceae, a small family of dwarf aquatics that were formerly interpreted as monocots, are instead a highly modified and previously unrecognized ancient lineage of angiosperms, indicating that water lilies are part of a larger lineage that evolved more extreme and diverse modifications for life in an aquatic habitat than previously recognized.
Abstract: The Hydatellaceae are small aquatic plants living modest lives away from the limelight, and conventionally assumed to be monocotyledonous flowering plants related to grasses. Now they have been subjected to the latest molecular techniques, and they turn out to be close relatives of basal angiosperms such as water lilies, increasing their importance immensely. They belong to a previously unrecognized lineage branching near the root of the angiosperms — a radical addition to the three deepest branches discovered in 1999 that rekindled interest amongst molecular biologists in the origin of angiosperms, what Darwin called an “abominable mystery”. Although the relationship of angiosperms to other seed plants remains controversial1, great progress has been made in identifying the earliest extant splits in flowering-plant phylogeny, with the discovery that the New Caledonian shrub Amborella trichopoda, the water lilies (Nymphaeales), and the woody Austrobaileyales constitute a basal grade of lines that diverged before the main radiation in the clade2,3,4,5,6,7,8. By focusing attention on these ancient lines, this finding has re-written our understanding of angiosperm structural and reproductive biology, physiology, ecology and taxonomy9,10,11,12. The discovery of a new basal lineage would lead to further re-evaluation of the initial angiosperm radiation, but would also be unexpected, as nearly all of the ∼460 flowering-plant families have been surveyed in molecular studies10. Here we show that Hydatellaceae, a small family of dwarf aquatics that were formerly interpreted as monocots, are instead a highly modified and previously unrecognized ancient lineage of angiosperms. Molecular phylogenetic analyses of multiple plastid genes and associated noncoding regions from the two genera of Hydatellaceae identify this overlooked family as the sister group of Nymphaeales. This surprising result is further corroborated by evidence from the nuclear gene phytochrome C (PHYC), and by numerous morphological characters. This indicates that water lilies are part of a larger lineage that evolved more extreme and diverse modifications for life in an aquatic habitat than previously recognized.
230 citations
TL;DR: The family Hydatellaceae was recently reassigned to the early-divergent angiosperm order Nymphaeales rather than the monocot order Poales, and several hypotheses on the homologies of reproductive units in Hy datellaceae are explored.
Abstract: The family Hydatellaceae was recently reassigned to the early-divergent angiosperm order Nymphaeales rather than the monocot order Poales. This dramatic taxonomic adjustment allows comparison with other early-divergent angiosperms, both extant and extinct. Hydatellaceae possess some monocot-like features that could represent adaptations to an aquatic habit. Ecophysiological parallels can also be drawn from fossil taxa that are known from small achene-like diaspores, as in Hydatellaceae. Reproductive units of Hydatellaceae consist of perianthlike bracts enclosing several pistils and/or stamens. In species with bisexual reproductive units, a single unit resembles an ‘‘inside-out’’ flower, in which stamens are surrounded by carpels that are initiated centrifugally. Furthermore, involucre development in Trithuria submersa, with delayed growth of second whorl bracts, resembles similar delayed development of the second perianth whorl in Cabomba. Several hypotheses on the homologies of reproductive units in Hydatellaceae are explored. Currently, the most plausible interpretation is that each reproductive unit represents an aggregation of reduced unisexual apetalous flowers, which are thus very different from flowers of Nymphaeales. Each pistil in Hydatellaceae is morphologically and developmentally consistent with a solitary ascidiate carpel. However, ascidiate carpel development, consistent with placement in Nymphaeales, is closely similar to pseudomonomerous pistil development as in Poales.
117 citations
TL;DR: It is shown that support for Amborella as the sole representative of the most basal angiosperm lineage is founded on sequence site patterns poorly described by time-reversible substitution models, and indicates that aquatic and herbaceous species dominate the earliest extant lineage of flowering plants.
Abstract: Correct rooting of the angiosperm radiation is both challenging and necessary for understanding the origins and evolution of physiological and phenotypic traits in flowering plants. The problem is known to be difficult due to the large genetic distance separating flowering plants from other seed plants and the sparse taxon sampling among basal angiosperms. Here, we provide further evidence for concern over substitution model misspecification in analyses of chloroplast DNA sequences. We show that support for Amborella as the sole representative of the most basal angiosperm lineage is founded on sequence site patterns poorly described by time-reversible substitution models. Improving the fit between sequence data and substitution model identifies Trithuria, Nymphaeaceae, and Amborella as surviving relatives of the most basal lineage of flowering plants. This finding indicates that aquatic and herbaceous species dominate the earliest extant lineage of flowering plants. [; ; ; ; ; .].
79 citations
TL;DR: A single genus of Hydatel-laceae, Trithuria, is distinguished, which consists of one species in New Zealand, ten species in Australia and two species in India, and is hypothesize that two south-western Australian endemics known as Hydatella dioica and Trithia occidentalis represent male and female individuals, respectively, of the same biological species.
Abstract: Hydatellaceae was traditionally circumscribed as a family of two genera, Hydatella and Trithuria. We place Hydatella in synonymy of Trithuria. We describe three new species of Hydatellaceae from northern Australia and one new species from south-western Western Australia. Thus, we distinguish a single genus of Hydatel-laceae, Trithuria, which consists of one species in New Zealand, ten species in Australia and one species in India. Two main characters were formerly used to distinguish between Hydatella and Trithuria: (1) reproductive units unisexual (homogamous) vs. bisexual (heterogamous) and (2) fruits with three prominent ribs, typically dehiscent vs. without prominent ribs, indehiscent. New evidence shows that the type of reproductive unit does not correlate with fruit morphology in Hydatellaceae. We hypothesize that two south-western Australian endemics known as Hydatella dioica and Trithuria occidentalis represent male and female individuals, respectively, of the same biological species. All four dioecious species of Hydatellaceae show similar sexual dimorphism. Male plants have reproductive units with longer and fewer involucral bracts than female ones. Anthers are much longer in dioecious species than in the morphologically closest cosexual species. The evolutionary significance of dioecy in Hydatellaceae is discussed.
60 citations
TL;DR: New data on endosperm development in the early-divergent angiosperm Trithuria (Hydatellaceae) indicate that double fertilization results in formation of cellularized micropylar and unicellular chalazal domains with contrasting ontogenetic trajectories, as in waterlilies.
Abstract: New data on endosperm development in the early-divergent angiosperm Trithuria (Hydatellaceae) indicate that double fertilization results in formation of cellularized micropylar and unicellular chalazal domains with contrasting ontogenetic trajectories, as in waterlilies. The micropylar domain ultimately forms the cellular endosperm in the dispersed seed. The chalazal domain forms a single-celled haustorium with a large nucleus; this haustorium ultimately degenerates to form a space in the dispersed seed, similar to the chalazal endosperm haustorium of waterlilies. The endosperm condition in Trithuria and waterlilies resembles the helobial condition that characterizes some monocots, but contrasts with Amborella and Illicium, in which most of the mature endosperm is formed from the chalazal domain. The precise location of the primary endosperm nucleus governs the relative sizes of the chalazal and micropylar domains, but not their subsequent developmental trajectories. The unusual tissue layer surrounding the bilobed cotyledonary sheath in seedlings of some species of Trithuria is a belt of persistent endosperm, comparable with that of some other early-divergent angiosperms with a well-developed perisperm, such as Saururaceae and Piperaceae. The endosperm of Trithuria is limited in size and storage capacity but relatively persistent.
45 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2019 | 3 |
| 2017 | 1 |
| 2016 | 1 |
| 2014 | 1 |
| 2013 | 3 |
| 2012 | 2 |