Skip to main content
ARS Home » Northeast Area » Washington, D.C. » National Arboretum » Floral and Nursery Plants Research » Research » Research Project #425386

Research Project: Taxonomy of Landscape Trees and Shrubs

Location: Floral and Nursery Plants Research

2014 Annual Report

The long-term objectives of this project are 1) to improve the understanding of interrelationships and the distribution of genetic variation (especially genome size and ploidy level) in understudied groups of specialty crops (primarily woody landscape plants), 2) to further develop the National Arboretum as a scientific resource, and 3) to investigate emerging and suspected invasive woody plants among groups of interest to the nursery industry and to National Arboretum plant introduction programs. These goals will be achieved through the following specific objectives: Objective 1: Identify and characterize genetic resources in understudied priority groups of woody landscape plants, including, but not limited to, Ulmus, Celtis, and Carya, to elucidate their genetic relationships and variation within species. Sub-objective 1.A. Determine taxonomic and genetic relationships among selected species of elms (Ulmus). Sub-objective 1.B. Determine ploidy level and comparative genome size in Carya using flow cytometry. Sub-objective 1.C. Determine the distribution of apomixis and polyploidy in North American species of hackberry (Celtis) and their taxonomy and relationships. Sub-objective 1.D. Resolve taxonomic problems and determine the amount and apportionment of genetic diversity in selected white oaks (Quercus sect. Quercus). Sub-objective 1.E. Carry out research projects to meet needs for taxonomic research expressed by stakeholders, such as the production of regional floras and botanical manuals in collaboration with other scientists and horticulturists. Objective 2: Maintain and enhance the National Arboretum Herbarium as a scientific resource and a collection documenting important agricultural research and germplasm. Sub-objective 2.A. Maintain and enhance the U.S. National Arboretum Herbarium as a scientific resource and a collection documenting important agricultural research and germplasm. Sub-objective 2.B. Maintain and enhance the U.S. National Seed Herbarium as a scientific resource and a collection documenting important agricultural research and germplasm. Objective 3: Determine the identity and basic biological characteristics of selected invasive woody plants in the United States. Apply herbarium records of woody plant introduction and naturalization in the mid-Atlantic area to test statistical models for predicting characteristics contributing to invasive behavior in woody plants.

Investigations will utilize a variety of different data types, primarily morphological data, DNA sequence variation, and variation in single-locus DNA markers within variable sites in the genome, analyzed using phylogenetic analyses and other multivariate statistical methods. Organisms will be studied in the field, herbarium, laboratory, and garden.

Progress Report
Elm research (Objective 1A) has concentrated on the Ulmus americana polyploid complex. Continuing fieldwork in the central and southern part of the species’ native range, from Tennessee and Alabama west to Texas, Oklahoma, and Kansas, has added a great deal to our knowledge of this germplasm. Flow cytometry on tissue from this area has improved our knowledge of the distribution of the ploidy races; living material has been brought back for propagation and potential future testing for disease resistance, and material was collected for future DNA analysis, which will allow many more populations of Ulmus americana to be characterized for different SSR markers. Studies of representative species of elm native to the Old World that are in cultivation in the United States are being carried out via a cooperative agreement with Morton Arboretum. Herbarium collecting is allowing the identifications of newly introduced germplasm to be checked and corrected where necessary. Study of their relationships using DNA sequencing has been delayed while the Cooperator was on research leave in Europe, but research plans are being made to complete the project next year. In collaboration with another ARS scientist, flow cytometry estimates were obtained of nuclear DNA content of representative Carya species (Objective 1B), including species whose ploidy level was previously unknown. Work continued on the taxonomy and the distribution of triploidy and apomixis in Celtis (Objective 1C). Chloroplast DNA sequences are being analyzed and work at additional herbaria (University of Texas Herbarium, Lundell Herbarium, U.S. National Herbarium, Boise State University Herbarium) has yielded additional morphological data, while flow cytometry of additional populations has revealed the presence of occasional diploids in the predominantly triploid species Celtis reticulata, previously believed to consist entirely of triploid populations. For Additional projects (Objective 1E), staff collected data on leafout time of 249 representative species as part of a multiyear study of factors influencing leafout time in collaboration with seven other gardens across the Northern Hemisphere. The first results of this study, analyzing data from 2011 and 2012, were submitted and published in New Phytologist. Staff also conducted research for sections of three important collaborative manual projects: the Flora of North America (Rubiaceae), Flora of Oregon (Rhamnaceae, Adoxaceae, Fagaceae and Caprifoliaceae), and the Vascular Plants of Northeastern United States and Adjacent Canada (Simaroubaceae, Hamamelidaceae, Platanaceae, and Menispermaceae), and submitted manuscripts for publication in all three of these books. Volume 3 of Steyermark's Flora of Missouri was published, containing several treatments written by staff. All of them will be important and widely-used sources of information on the native and invasive plants of the United States, and all of them will be used by horticulturists, botanists, land managers, educators, and conservationists throughout the United States, insuring that work on native plant horticulture, invasive species management, and plant conservation will be based on full, accurate and up-to-date information about the basic biology and relationships of these organisms. In addition, staff participated in a trip to three of the most important herbaria in China to carry out research on the taxonomy of Asian Catalpa species, in support of the project "Evaluation and Genetic Improvement of Woody Ornamental Landscape Plants for Disease and Pest Tolerance, Non-Invasiveness, and Ornamental Traits." A manuscript on classification of the genus Catalpa and the related genera Chilopsis and X Chitalpa is in preparation. Activity in the herbarium (Objective 2A) centered around the job of moving the specimens back into the building and reorganizing the approximately 800,000 specimens following the 2010-2013 renovation of the main building at the National Arboretum. This work involved cleaning and reorganizing the spaces the herbarium occupies and moving 520 boxes of specimens from storage (in Suitland MD) and filing them in their proper places in the collection. Completing the move has taken a great deal of time, but having a renovated building with adequate climate control will benefit the herbarium. Staff is now catching up with the backlog of work, especially filing that could not be done during the 2.5 year period when most of the collection was inaccessible during the renovation. The specimens in the herbarium provide material that is essential for our research program and for identification of plant material for researchers and the nursery industry. They also provide an important scientific record of past research and plant breeding work across USDA, and commercial releases that resulted from our work. Staff and volunteers have added approximately 3,500 records to the herbarium database. Herbarium collecting has involved the collection of voucher specimens of the living collections at the National Arboretum, collections documenting important cultivated plant collections in the Pacific Northwest through a cooperative agreement with the University of Washington Arboretum in Seattle, and collecting associated with the Ulmus americana and Celtis research projects. Altogether, approximately 500 specimens were collected, 2000 specimens mounted and added to the main herbarium. We continue to loan and exchange specimens with other herbaria around the world. Approximately 220 boxes of books were moved back from storage, and they are being filed. The herbarium staff trained an intern in techniques of herbarium management. Our cooperative agreement with the University of Washington Arboretum ended this year. Over the course of the agreement, we received a total of 3,106 specimens consisting of 974 taxa, including a good representation of ornamentals cultivated in the Pacific Northwest. In addition, the project provided financial support for students learning herbarium techniques at the University of Washington Arboretum. In the U.S. National Seed Herbarium (Objective 2B), approximately 320 seed samples of Poacaeae and Rubiaceae were cleaned, relabeled, hermetically sealed in plastic bags and filed. For the invasive risk assessment project (Objective 3), species on the target list are being coded for geographical area of origin, invasive status, and selected biological traits used in weed risk assessment, and approaches to data analysis have been discussed with possible collaborators.


Review Publications
Panchen, Z., Primack, R., Nordt, B., Ellwood, E., Stevens, A., Renner, S., Willis, C., Fahey, R., Whittemore, A.T., Du, Y., Davis, C. 2014. Leafing out phenology in woody plants of the Northern Hempisphere show phylogenetic, ecological and anatomical patterns. New Phytologist. DOI: 10.111/nph.12892.
Whittemore, A.T. 2014. Ulmaceae for Flora of Missouri. Flora of Missouri. 1178-1192.
Parfitt, B.D., Whittemore, A.T. 2013. Ranunclulaceae. Flora of the San Juan Basin. 877-895.
Whittemore, A.T. 2014. JUGLANDACEAE. Flora of Missouri. 282-294.