Phylogeny of North American <i>Dichanthelium</i> (Panicoideae, Poaceae): Testing Species Limits in One of the Most Taxonomically Complicated Groups of Grasses
Bibliographic record
Abstract
Premise of research. Dichanthelium extends from Canada to Argentina and is most species rich in eastern North America. These C3 panicoid grasses, which are mixed mating and flower two or three times per year, displaying different vegetative growth forms over that time, are renowned for their taxonomic complexity. Thus, there are drastically differing taxonomic treatments; however, no well-sampled phylogenetic perspective is yet available to further explore relationships among species or species complexes. Methodology. We developed the first broadly sampled phylogeny of Dichanthelium, covering the entire range of the genus, but with a focus on the species-rich eastern North American distribution. We sampled 72 taxa (290 accessions), including all currently recognized taxa in the recent Flora of North America treatment. Our dataset consisted of the plastid locus rpl32-trnL and the nuclear loci internal transcribed spacer (ITS) and granule-bound starch synthase I (GBSSI) and was analyzed using maximum likelihood. We calibrated our phylogeny to test the divergence time of the North American clade and likewise used ITS data to explore putative hybridization. Pivotal results. South American species of Dichanthelium formed a grade of successive sisters to the North American clade, which we recovered as originating in the late Miocene–early Pliocene. We recovered 27 subclades, most of these representing species complexes or morphologically similar species. Numerous taxa were resolved outside of their putative species groups and are apparently morphologically cryptic species. We show several cases of putative hybridization in eastern North American and Hawaiian species. Conclusions. Our phylogeny provides a foundation for understanding this taxonomically complicated group of grasses, which will need detailed future studies into species complexes to provide greater taxonomic resolution and understanding of biological processes driving the evolution and diversification of the clade. This should include further study of autogamy and its evolutionary consequences in North American taxa. We propose an adjusted taxonomic treatment of specific members of the genus based mostly on our phylogenetic results.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".