Thomas J. Givnish
Henry Allan Gleason Professor of Botany and Environmental Studies
Ph.D. (1976) Princeton University • 315 Birge Hall • 608-262-5718 • givnish@wisc.edu
Plant ecology and evolution; adaptive radiation and molecular systematics;
phylogeography; physiological ecology; landscape dynamics
Over the past decade, my colleagues and I at six major North American institutions have conducted extensive research to document the evolution of the economically most important group of plants on earth – the monocots – supported by grants from the Assembling the Tree of Life (AToL) Program and the Systematics Program at the National Science Foundation,
Monocots comprise more than 65,000 species of flowering plants, including such groups as grasses, sedges, palms, gingers, bananas, orchids, onions, yams, pondweeds, and philodendrons. They occur in almost all habitats on Earth, and provide the basis for the great majority of the human diet. Monocots also account for much of the commerce in cut flowers and horticultural bulbs such as crocuses, irises, hyacinths, tulips, and lilies. Previous attempts to analyze relationships among different monocot groups have made substantial progress but have fallen short, perhaps because many major groups diverged more than 90 million years ago, leaving only subtle and difficult-to-detect traces of deep relationships in their form and genetic material.
My colleagues and I used a new approach to develop a definitive family tree for the monocots. For the first time, we sequenced and analyzed hundreds of whole chloroplast genomes (the circles of DNA inside the green organelles that conduct photosynthesis). Almost all previous studies using DNA to infer plant relationships have relied on sequences of only one or a few genes or spacers between genes. Our phylogenomic approach provided sequences for more than 80 chloroplast genes and, in some cases, the spacers between them, providing an avalanche of new data with which to assess evolutionary relationships. Our analyses have shifted the positions of 16 monocot families, and provided the basis for studies of trait evolution and historical biogeography in several groups. Research led by my lab led to the first fully resolved and strongly supported backbone phylogeny of the orchids – the largest family of angiosperms – and led to tests of the morphological and biogeographic drivers of their extraordinary diversification. We also led analyses of evolution in the order Liliales, synthesized our phylogenomic conclusions regarding the monocots as a whole, quantified how the resolution of and support for species relationships depends on branch length, branch depth, and number of loci used, and advanced a new, function-based model for the origin of monocots as underwater aquatic plants.
Our MonAToL team has also sequenced dozens of transcriptomes – that is, the entire complement of RNA expressed in tissues, primarily from nuclear DNA – from the leaf tissue of representatives of all monocot orders. The unparalleled amount of genetic information from both the plastid and nuclear genomes has allowed us to conduct some of the most powerful analyses to date of relationships among any group of organisms.
Currently, my colleagues and I – including post-doc Nisa Karimi, Alan Lemmon, and Emily Lemmon, and several taxon-specific specialists – are using phylogenomic data from hundreds of single-copy nuclear loci and whole plastomes to reconstruct the phylogeny, historical biogeography, and patterns of diversification in Calochortus and Lilium. The study of lilies worldwide will include tests of quantitative convergence on floral syndromes associated with pollination by butterflies, hawkmoths, hummingbirds, and bees, respectively, in the 21 North American species, as documented by my student Mark Skinner. We are also re-examining evolution in the Hawaiian lobeliads using phylogenomic data.
Monocot AToL PIs:
Cecile Ané
Jerry Davis
Claude dePamphilis
Tom Givnish
Alejandra Gandolfo
Sean Graham
Jim Leebens-Mack
J. Chris Pires
Dennis Stevenson
Wendy Zomlefer
© 2021 University of Wisconsin Department of Botany
Last updated: 27 November 2021
