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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

2018 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
This is the final report for Project 8020-21000-070-00D, which ended on 3/19/2018 and was replaced by 8020-21000-080-00D. Significant progress was made on all three objectives, which fall under NP301. We continued to collect material of Fraxinus (ash) with collaborators, determining the ploidy using flow cytometry and collecting material for DNA extraction. Our primary aim this year was to better characterize the southeastern ash species. Our planned extraction techniques for next-gen DNA sequencing of ash produced DNA with insufficient fragment size, probably because of the collection protocol. Improved techniques are being tested in the lab of a collaborator. This work is allowing us to improve sampling of this valuable but critically imperiled germplasm. We checked, and in many cases corrected, identifications of elm species in the living collections of the National Arboretum, the ARS Woody Landscape Plant Germplasm Repository, and the Morton Arboretum, especially those used as samples for a radSeq-based phylogeny of the genus that we are preparing. Genetic marker (SSR) data was also gathered for the analysis of possible hybrid elms. For our studies of Quercus (oaks), a set of HybSeq baits for next-gen DNA was prepared in the lab of a collaborator to use for targeted sequencing of representative species of oaks, including loci functioning in drought resistance and spring budbreak, and these are being tested in the lab of a collaborator. This will allow us to directly characterize oaks for genes that affect physiological characteristics that are important for nursery use. A manuscript describing the native and escaped hollies (Aquifoliaceae) of North America, with identification aids, was completed and submitted. In collaboration with the Gardens Unit, a list of cultivars registered in the period March 2013 - November 2016 was published. In collaboration with scientists at five botanical gardens in North America, Germany, and China, we published an analysis of the effects of climate on fruit phenology, based on data from 406 species of plants. Herbarium management has made good progress despite the absence of a permanent curator, an essential position. For the main herbarium, over 3000 records were added to the database, and several hundred specimens, including many collections documenting recent research and germplasm projects, were added to the collection. For the seed herbarium, 200 more specimens, representing additional taxa not previously held in the seed herbarium, were added. We continued to survey escaped populations of ivy, a genus important in horticulture that has become invasive in the United States, from across North America for genome size and morphology, in order to determine the distribution and degree of invasiveness for different species. Preliminary SSR markers, useful for investigating possible hybrids, were run and results are being analyzed. Additional triploid ivies were discovered and brought into cultivation, so we can test them to determine whether they are able to produce seed. This work allows us to determine the relative invasiveness of different cultivated ivies, and to look for less invasive alternatives for the species of ivy now on the market.


Review Publications
Whittemore, A.T., Campbell, J.J., Xia, Z., Carlson, C.H., Atha, D., Olsen, R.T. 2018. Ploidy variation in Fraxinus L. (Oleaceae) of eastern North America. International Journal of Plant Sciences. 179(5):377-389. Available: