Report 2002: Status and Recommendations

Version 7.0 - October 2002


The woody landscape plants grown in the United States comprise 1200 to 1500 genera of trees, shrubs, groundcovers, and vines from around the world (See Appendix 1). Landscape plants enhance the quality of life by directly affecting aspects of aesthetic, environmental, and psychological well-being. Landscape plants contribute to the vitality of public, commercial, and recreational spaces, as well as add to the value of residential property. With increasing concerns regarding air pollution, noise abatement, energy conservation, and climatic change, the potential for landscape plants to ameliorate these problems makes it critical that we strive to develop improved trees and shrubs and expand the diversity of species in our communities. Environmental horticulture ranks third in the nation in gross agricultural cash receipts with an estimated $49 billion economic impact. This industry, consisting primarily of small family businesses, creates nearly half a million jobs. In addition, many plants with landscape value are also important for food, medicine, fiber, building materials, and to solve natural resource problems. Consequently, woody landscape plants represent a natural resource of considerable economic and strategic importance to the United States.


The function of the Woody Landscape Plant Crop Germplasm Committee (WLPCGC) is to serve the landscape nursery industry, consumers of its products, and the germplasm research community, by providing input to individuals and organizations, such as the U.S. Department of Agriculture's (USDA) Agricultural Research Service (ARS), State Agricultural Experiment Stations, and others, on technical matters relating to woody landscape plant germplasm management. The WLPCGC also serves as a facilitator for information dissemination, germplasm management, and partnership formation. Along with providing recommendations to USDA, the purpose of this report is to heighten the awareness of germplasm activities in the public, private, and commercial sectors; foster better coordination among sectors; and to enhance the acquisition, preservation, conservation, and utilization of woody landscape plants.

Status of Crop Vulnerability

While there is great potential for many different genera and species to be used as landscape plants, the genetic base of individual species under cultivation is often narrow. In fact, some woody landscape plants are represented by only a single clone. Moreover, many urban landscapes rely upon just a few species. For instance, green ash, redtip photinia, American sycamore, honeylocust, silver maple, Indian hawthorn, and Bradford pear are all used extensively in certain regions. Such a narrow genetic base results in increased vulnerability to catastrophic loss by insects, diseases and environmental stress. Several woody landscape plant species have suffered devastating losses to diseases and insects during the past 50 years. Extensive plantings of American elm resulted in major losses of urban street trees due to Dutch elm disease, beginning in the 1950s. During the same time period, the Lethal Yellowing phytoplasma decimated vast numbers of Atlantic Tall coconut palms in Florida. More recently, the imported wooly adelgid has caused widespread destruction of hemlocks in the eastern United States.

Many woody plant species currently maintained in the National Plant Germplasm System (NPGS) are represented by only a single accession. This situation is unacceptable from the standpoint of maintaining a sufficient variety of genotypes for enhancement, breeding, and conservation of genetic diversity.

While there are still many opportunities to collect plants, accelerated changes in land use, degradation in soil, water and air quality, and changes in the political climate towards plant collecting will continue to decrease genetic diversity in natural populations and restrict access to genetic resources in many key locations. Thus, it is imperative that the genetic base of vulnerable target species be expanded while opportunities allow.

Since the Convention on Biological Diversity (CBD) entered into force in 1993, the free and open access to genetic resources from other countries has greatly diminished. The regulation of access to genetic resources was fundamentally changed by the CBD, which became international law on 29 Dec. 1993. The CBD, now ratified by 179 countries, is an international treaty dealing with the conservation and sustainable use of biological diversity, and the sharing of benefits arising from the use of genetic resources.

Article 15 of the CBD recognizes that nations have sovereignty over their genetic resources, and provides that access to them is subject to prior informed consent from the national government and mutually agreed terms on the sharing of benefits derived from their use or commercialization. The implementation of the CBD presents challenges for germplasm source countries, as well as for those desiring access to foreign genetic resources. Countries who are party to the CBD were directed to enact national legislation regulating access to genetic resources, yet procedures for implementing these laws remain to be completed in many countries. Notably, the CBD specifies that countries should create conditions to facilitate access to genetic resources, and not impose restrictions that impede use of those resources.

State of the Nursery and Landscape Industry

The nursery and landscape industry includes thousands of small family businesses that grow, retail, install, and care for plants and landscapes. The industry employs approximately 500,000 workers during peak seasons. According to the USDA's Economic Research Service, the nursery and greenhouse industry comprises the fastest growing segment of U.S. agriculture. For example, while the number of U.S. farms of all types has declined over the last two decades, the number of nursery and greenhouse farms has increased. Grower cash receipts from nursery and greenhouse sales have grown steadily over the last two decades and are increasing at approximately $500 million per year. In 1997, nursery and greenhouse operations had sales of $10.9 billion, up 43 percent from 1992. Of 18,860 nursery-crop farms, 650 (3.5 percent) had sales over $1 million. Woody landscape plant products account for 57.5% of all nursery and greenhouse crop value.

The U.S. is the world's largest producer of and market for woody landscape crops. These crops represent an important and unique segment of agriculture whose impact is felt on the national, state, and community level. Nursery and greenhouse crops represent the third most important crop sector in U.S. agriculture. Nursery and greenhouse crops are among the top five commodities in 27 states and the top 10 commodities in 42 states. Sixty-nine million U.S. households spent $30.1 billion at retail lawn and garden outlets in 1998, according to The National Gardening Association and The Gallup Organization, while over 21 million households spent $16.8 billion on professional landscape, lawn, and tree care services.

Breadth of Woody Landscape Plant Research Activities

There are many institutions, both public and private, engaged in projects involving woody landscape plant germplasm. However, in most cases, there is limited financial support for and little coordination of these efforts. Often these activities are left to the discretion of current staff with no established institutional policies to ensure continuity. Thus, there are many areas of overlap in activities and also many major voids.

In order to determine the potential value, impact, and importance of the nation's woody ornamental germplasm, the WLPCGC conducted several informal surveys to identify stakeholders, determine their missions, and assess the relative importance of woody ornamental activities relative to other crops.

The American Society for Horticultural Science (ASHS) is the largest, most visible organization in the U.S. dedicated to advancing all facets of horticultural research, education, and application, with almost 4000 members from research, universities, government, and industry. To get an estimate of the how many of these members focus on ornamentals, a quick survey of the listings of working groups in its 2000 Membership Directory was undertaken. It revealed that, of those U.S. members who listed a working group, approximately 20% associated themselves with the Nursery, Ornamental/Landscape/Turf, Propagation, and/or Ornamental Plant Breeding working groups.

In addition, an email survey was sent specifically to nursery and ornamental working groups and colleagues in October 2001. Responses from 16 university scientists and 6 ARS scientists, who conduct breeding or selection of woody ornamental landscape plants, revealed that over 62 genera are represented by the activities of these 22 scientists alone.

Structure of Woody Landscape Plant Germplasm Resources in the United States

Woody landscape plant germplasm is conserved by numerous institutions both within and beyond the National Plant Germplasm System (NPGS). The following sections describe institutions with significant conservation efforts and the roles they play.

National Plant Germplasm System (NPGS)

The NPGS is one of the components of the U.S. National Genetic Resources Program which also conserves genetic resources of animals, microbes and invertebrates. The mission of the NPGS is to collect, document, maintain, evaluate, enhance, distribute and preserve the plant genetic resources necessary for improving the quality and production of economic crops important to U.S. and global agriculture.

National Germplasm Resources Laboratory (NGRL)

The role of the NGRL is to support the germplasm activities of the working and base collections of the NPGS through the development, enhancement and maintenance of the system-wide database, Germplasm Resources Information Network (GRIN); facilitate the acquisition of new germplasm for the NPGS through maintaining germplasm exchange and plant exploration programs and liaison with U.S. quarantine regulators; help identify needed germplasm for the NPGS; assist in the proper documentation of new germplasm; and coordinate and facilitate the activities of the Crop Germplasm Committees. The Database Management Unit (DBMU) and the Plant Exchange Office (PEO) manage the various activities of the NGRL. The DBMU develops and administers the computerized database information on all germplasm maintained within the NGRL. This database, GRIN, is available at the website: Available information on all NPGS accessions includes passport, accession, inventory and evaluation data, and needed germplasm can be requested directly through this site. The NPGS curators load and maintain these data for their assigned crops. The PEO manages the USDA/ARS Plant Exploration/Exchange Grant program to acquire needed germplasm for the NPGS. Scientists develop proposals according to PEO guidelines. The proposals are first reviewed by the appropriate Crop Germplasm Committee to insure that they support their priorities. Once proposals pertinent to woody landscape plants are endorsed by the WLPCGC, the grants are reviewed by a subcommittee of the NPGS for possible funding. The PEO works with the proposed host country to obtain the necessary access to their germplasm and develops any required agreements concerning the use, ownership and distribution of the germplasm. Collected germplasm and documentation are forwarded to the appropriate NPGS collection where they are maintained according to NPGS policy. PEO also supports the NPGS by facilitating NPGS distributions, maintaining liaisons with USDA/APHIS, assigning the NPGS PI numbers, helping determine NGPS germplasm needs, participating in plant explorations, and developing international collaborations to support germplasm activities.

Pertinent National Plant Germplasm System Repositories

Within the NPGS, a network of active sites located throughout the U.S. manages working collections of a diverse array of plant germplasm and associated information. A summary of all relevant NPGS active sites is presented in the following table. Information on the sites can be found at Active sites deal directly with germplasm users and are dedicated to making germplasm and information available for research and crop improvement. Twelve of these sites are conserving important collections of woody landscape plants. The most comprehensive collections are managed by the Woody Landscape Plant Germplasm Repository (WLPGR) in Glenn Dale, MD and Washington, DC. The overall objectives of the WLPGR are to introduce, maintain, and distribute diverse and wild-origin genetic resources of trees and shrubs for landscape use through collection, exchange, and evaluation. Woody plant germplasm is also evaluated for production potential and further characterized using biochemical and molecular DNA technologies. The repository is responsible for maintaining 182 genera. More than 1,400 accessions of seeds are maintained in a medium-term storage facility, and 2,800 plants are maintained on the grounds at Beltsville and Glenn Dale, MD, and Washington, DC. The site at Glenn Dale, where most of the in-ground collection is maintained, is scheduled to close in 3-7 years. Preparations are being made to relocate this germplasm to a site in Beltsville, MD. The Curator of the WLPGR can use the expertise of the WLPCGC and this Status Report to guide decisions regarding physical aspects of the move as well as broader germplasm issues.

NPGS active sites with important collections of woody landscape plants.
Site Location Pertinent Collections Form Held
Woody Landscape Plant Germplasm Repository Glenn Dale and Beltsville, MD, and Washington, DC ca. 180 genera Plants, seeds
North Central Regional Plant Introduction Station Ames, IA ca. 30 genera Seeds, plants
National Clonal Germplasm Repository Brownwood and Somerville, TX Carya Plants
National Clonal Germplasm Repository Corvallis, OR Amelanchier, Corylus, Cydonia, Pyrus, Riber, Rubus, Sambucus, Sorbus, Vaccinium Plants, seeds
National Germplasm Repository Davis, CA Actinidia, Diospyros, Ficus, Juglans, Morus, Olea, Pistacia, Prunus, Punica, Vitis Plants
Plant Genetic Resources Unit Geneva, NY Malus, Prunus, Vitis Plants, seeds
Plant Genetic Resources Management Unit Griffin, GA Hibiscus, Indigofera, Leucaena, Pueraria, Senna, woody legumes Seeds, plants
Tropical Plant Genetic Resource Management Unit Hilo, HI Artocarpus, Averrhoa, Bactis, Canarium, Carica, Dimocarpus, Litchi, Macadamia, Malpighia, Nephelium, Passiflora, Psidium Plants
Tropical Agriculture Research Station Mayaguez, PR Tropical genera Plants
National Germplasm Repository Miami, FL Tropical genera Plants
Western Regional Plant Introduction Station Pullman, WA Amorpha, Artemisia, Genista and various range shrubs Seeds, plants
National Clonal Germplasm Repository Riverside, CA Citrus and related Rutaceae, Phoenix Plants

Base Collection: National Center for Genetic Resources Preservation (NCGRP)

NPGS working collections are made more secure through intentional duplication in a base collection designed for long-term conservation. The NPGS base collection is managed by the NCGRP (formerly known as the National Seed Storage Laboratory) in Fort Collins, CO. The NCGRP, through its two plant-oriented research units, services active sites by providing back-up under the best possible storage conditions and by developing and testing protocols that improve long-term preservation and viability monitoring. In addition, the NCGRP houses collections for the Plant Variety Protection Office, the Center for Plant Conservation, and various other institutions. The NCGRP does not generally distribute its collections directly to users, but collaborates closely with curators at the active sites to improve overall levels of conservation and management and their interactions with a diverse community of users.

At present, only small proportions of most of the pertinent woody landscape plant germplasm collections are backed up at the NCGRP, but the Center is conducting research on preserving clonal materials (including vegetative buds) under cryogenic conditions, which should accelerate the back-up process.

USDA Natural Resources Conservation Service

The Natural Resources Conservation Service (NRCS) Plant Materials Program collects plants and develops plant science technologies for the successful conservation of natural resources. The program consists of a network of Plant Materials Centers and Plant Materials Specialists strategically located throughout the United States, which together provide conservation solutions for critical habitats, environmental concerns, management practices, and key farm and ranch programs. The collection of native (and in some cases non-native) woody species by the Plant Materials Program represents a tremendous germplasm resource. Currently, a limited amount of NRCS germplasm is submitted to NPGS for long-term preservation. Many of the species collected by NRCS can be evaluated for ornamental or landscape use, in addition to conservation uses. More information on the Plant Materials Program can be found at: .

USDA-Forest Service

Activities to conserve genetic diversity of forest species by the US Forest Service have been minimal to date. Beyond the holdings of the Center for Conservation of Genetic Diversity in the Institute of Forest Genetics at Placerville, CA, which maintains important collections of a few major species and several with restricted ranges, few, if any, materials are maintained with long-term genetic conservation as a goal. With a few notable exceptions, much diversity exists in natural populations and also in seed orchards and provenance studies at USFS installations. None of these collections has been managed with conservation of genetic diversity as a primary goal. Documentation of ex situ collections is uneven and non-standardized. Recommendations for a comprehensive strategy to conserve forest genetic resources have been developed but funding has not been approved. (see The Status of Temperate North American Forest Genetic Resources. Report No. 16, University of California Genetic Resources Conservation Program, Davis, CA, D.L. Rogers and F.T. Ledig (eds.).

American Association of Botanic Gardens and Arboreta (AABGA)

The plant collections of North American botanical gardens and arboreta are major repositories of genetic resources from throughout the world. The plant collections of numerous institutions contain rare or endangered species, documented wild-collected species, modern and historic cultivars, botanically complete collections, as well as genetically diverse collections.

With nearly 300,000 accessions growing on approximately 100,000 acres of North American gardens, these collections represent priceless genetic repositories. They are vital to horticultural and botanical research, breeding programs, nursery industry production, conservation efforts, and pharmaceutical research. Information on many of the collections held by AABGA member institutions is accessible through the AABGA Collections Directory.

Despite superb individual collections, until recently there has been little coordination among gardens sharing similar collection interests. Efforts are often duplicated, and clonal material passed from garden to garden, while other rare or otherwise important genetic resources remain unprotected.

Established by the American Association of Botanical Gardens and Arboreta in the early 1990s, the North American Plant Collections Consortium (NAPCC) has two primary purposes: 1) to coordinate a continent-wide effort among botanical gardens for the conservation of plant genetic resources and biodiversity; and 2) to act as a mechanism for elevating curatorial standards for the management of plant collections.

NAPCC can be a powerful force in conserving crucial plant genetic resources. By creating collective inventories and analyzing the data, the NAPCC can identify redundancies as well as gaps in North American plant collections. At the same time, NAPCC involvement in the development of focused management plans for target collections can ensure that significant collections are systematically replicated to protect plant genetic resources from potentially catastrophic events.

No single organization has the resources to acquire and manage the ornamental plant genetic resources of the world. In 1995, AABGA and the United States Department of Agriculture-Agricultural Research Service (ARS) entered into a Specific Cooperative Agreement to support the development of the NAPCC program. This NPGS collaboration with AABGA has enormous potential for dramatically expanding the conservation, management and utilization of plant genetic resources. To date, ARS has partially funded a part-time NAPCC Coordinator and the production of publicity materials promoting the development of collections for targeted conservation.

In return, the NAPCC plant collections will greatly expand the availability of plant genetic resources to the NPGS and the broader user community for carrying out their missions. While retaining complete autonomy of its own program, each NAPCC member is a NPGS associate germplasm repository for the taxonomic, horticultural or other grouping it has defined.

Private Collections

There is a significant and unreported amount of woody plant crop germplasm outside the formal plant germplasm preservation community. This germplasm is held and maintained by individuals and institutions ranging from personal collections to nurseries and universities. Germplasm in these holdings varies significantly in the quality and completeness of its documentation; however, many taxa have been systematically collected and preserved. Many of these holdings have been assembled by private individuals, nursery professionals and university researchers engaged in international plant exploration, collection and importation activities, but are not part of the NPGS or other documented collections. Without knowledge about the quality, quantity and location of these holdings, the plants are unavailable as genetic resources. Plant societies, nursery professionals, public garden professionals and university personnel may be able to provide information on or access to this germplasm.


Although not necessarily associated with living collections, the numerous herbaria affiliated with arboreta, botanic gardens, universities, and museums constitute a valuable resource for woody landscape plant germplasm, as they serve critical roles as repositories for vouchers of living collections, plant identification and systematics, and documentation of the extent and characteristics of natural distributions.

Germplasm Holdings

In cooperation with the NGRL, curators, and others, the WLPCGC developed a prioritized working list of woody landscape genera, along with information on the number of research programs utilizing each genus and on sites holding significant collections, both within the NPGS and outside, such as in the NAPCC (Appendix 1). Genera were ranked on a scale of 1 to 4 according to perceived importance to economic, aesthetic, or environmental well-being. Genera with which respondents were not familiar were not ranked. It became apparent that tropical genera, although important to woody landscape plant germplasm, represented a significant portion of the list, and should probably be ranked separately. Thus, there are currently two lists, one for temperate plants, and one for tropical plants. The prioritized lists can be used as an aid in acquisition, preservation and the establishment of collaborative relationships with other institutions.

Status of Woody Landscape Plant Germplasm Acquisition – Exploration & Exchange

The acquisition of both foreign and domestic plant germplasm through exploration and exchange is vital to enhance plant diversity, and drives the sustained growth of the nursery and landscape industries. Plant exploration activities have not always been coordinated with preservation; consequently, the germplasm and the associated information on many of these resources are no longer available. In the past decade, the NPGS has developed effective protocols for obtaining access to plant genetic resources in many countries, established ethical and standardized plant collecting methods, and has continued to support numerous explorations. In addition, successful explorations have been conducted by botanic gardens, as well as under commercial, university, and individual sponsorship. However, international law now dictates that genetic resources are a sovereign resource of the country of origin and no longer the common heritage of humankind. Consequently, access to plant genetic resources in many countries is limited. New strategies involving increased collaboration and additional resources are now required to continue plant exploration and exchange activities. Additionally, the importation of germplasm carries inherent risks, such as the introduction of potentially invasive plants and other biological pests.

Several arboreta have been involved in plant exploration activities. These include the National Arboretum, the Holden Arboretum, Morton Arboretum, Chicago Botanic Garden, Morris Arboretum of the University of Pennsylvania, Longwood Gardens, University of Washington Arboretum, Missouri Botanical Garden, Arnold Arboretum, Rancho Santa Ana Botanic Garden, Desert Botanic Garden, Fairchild Gardens, and Lyon Arboretum. Plant exploration and collecting has also been improved by the formation of consortia. Examples include the North American/China Plant Exploration Consortium (NACPEC) and the Midwest Plant Collecting Collaborative.

The WLPCGC is currently assessing plant collections to determine if priority genera are represented by known sources and include good representation of available genetic diversity. Based on this assessment, future collection/exchange programs can be tailored to fill gaps in species, collection locations, or specific traits.

Germplasm Preservation and Maintenance

The preservation and maintenance of ornamental germplasm are the most resource intensive components of collections activities. Curatorial standards often vary among sites. These activities are frequently under-funded. Preservation of non-clonal material may involve cycles of renewal by seed or vegetative propagation, while clonal material is usually renewed only by vegetative means. Non-clonal collections can also be maintained via long-term storage of seed, whereas clonal collections have traditionally depended on maintenance of field or greenhouse accessions. Advances in long-term in vitro storage and cryopreservation of clonal germplasm may ease this burden in the future. Due to limited resources, the preservation and maintenance of ornamental germplasm has to be prioritized by consensual standards of importance to its end-users.

The American Forestry Association ( has identified a number of Grand Champion trees, many of which have landscape value or grow in managed landscapes. In addition, there are a number of heritage trees throughout the U.S., prominent because some historical event is associated with them. In order to preserve this old and historic germplasm, groups of university scientists and some private nurseries are involved in attempts to propagate from these trees.

Status of Woody Landscape Plant Evaluation Activities

The initial characterization and field evaluation of landscape plant germplasm have been undertaken by numerous institutions on many separate occasions, as part of organized introduction schemes, breeding and selection projects, and other trials and scientific studies. While many botanic gardens, universities and nurseries continue to conduct these projects, to date, there have been few attempts to standardize the collection of these data, and retrieval of such data by potential users can be difficult. Results are often limited in value because of lack of knowledge of origin of the material under evaluation. This pitfall, coupled with the tendency to make broad recommendations, often results in erroneous conclusions about a species' adaptability. Plants of the same species from various parts of its native range often may give different results.

Another limitation of these efforts is that evaluation criteria are usually based on evaluation for direct use only and not on genetic potential for use in a breeding program. Thus, plants that may have possessed some outstanding characteristics have often been discarded because of limitations in general adaptation or other characteristics. Plant germplasm should be characterized for all important traits, including disease and insect resistance, foliar and floral characteristics, plant habit, and tolerance to various environmental stresses.

Provenance trials and biosystematic studies are also used to evaluate woody plant germplasm. The primary limitation of these reports is a lack of information on aesthetic or landscape characteristics, as well as limited scope. These studies are often not linked with germplasm preservation.

At present, there are projects underway to develop standardized databases containing pertinent evaluation data. These projects have been initiated for a variety of purposes on limited groups of genera, and little effort has been made to coordinate their activities. Such projects include the USDA-Natural Resources Conservation Service's Woody Plant Evaluations made by Plant Materials Centers for conservation purposes. In 1995, the WLPCGC developed a general framework of basic descriptors for characterizing and evaluating woody landscape plant germplasm in GRIN. Other efforts are the description systems established by the Malus, Pyrus, Prunus, Juglans, Vitis, and Small Fruits Crop Germplasm Committees for GRIN (primarily for characteristics dealing with fruit and nut production, although some descriptors will clearly be useful to other users). An additional activity is the compilation of The Directory of Landscape Tree Cultivars sponsored by the Horticultural Research Institute for named cultivars of shade and street trees. Of these examples, only the GRIN system is directly connected to germplasm preservation.

NC-7 Regional Ornamental Plant Trials

The NC-7 Regional Ornamental Plant Trials began in 1954 through the efforts of a small group of dedicated horticulturists led by Professor S.A. McCrory of South Dakota State College (now University). The Trials began with the ultimate goal of expanding the range of knowledge about useful plants for the region's nursery trade. To this end, the emphasis of the Trials is placed on detailed, long-term evaluations of plant survival, growth and aesthetic characteristics at a broad range of sites rather than on promotion of new plants. However, trial site cooperators do collaborate to varying degrees with their local nursery industry to introduce promising materials. The Trials rely on a network of horticultural cooperators at about 30 sites located throughout the North Central region and in other states with similar climatic characteristics. Cooperators are located at land-grant universities and experiment stations, public gardens, and the region's four USDA-NRCS Plant Materials Centers. There are now nearly fifty years of data collected from ten-year trials of more than 500 accessions of landscape trees, shrubs and vines, including a much wider range of genera than are maintained at the North Central Regional Plant Introduction Station. Data on plants distributed for testing since 1984 are held in a database available on the Internet at: and, when possible, are also linked to accessions in the GRIN database.


The Southern Extension and Research Activities/Information Exchange Group - 27 is sponsored by the Southern Association of Agricultural Experiment Station directors and Southern Extension directors. Representatives from extension and research programs from thirteen land-grant universities and the U.S. National Arboretum cooperate to evaluate ornamental plant germplasm adaptable to the southeastern U.S. The objective of the group is to identify, evaluate, select, and disseminate information on superior, environmentally sustainable landscape plants for nursery-crop production and landscape systems in the southeastern U.S. The group is currently evaluating 10 woody plants, although evaluation reports are not yet available.

Canadian Evaluation Programs

There are two ongoing evaluation programs for woody landscape plants in Canada: the Prairie Regional Trials for Woody Ornamentals (PRTWO) and the Alberta Regional Woody Plant Test Program (ARWPTP). A third evaluation program at sites across Quebec, originally coordinated by the Atelier "Réseau d'essai des plantes ligneuses ornementales du Québec" of the Conseil des Productions Végétales du Québec (now the Centre de Référence en Agriculture et Agroalimentaire du Québec), was recently discontinued. It produced a series of evaluation reports available from Agriculture and Agri-Food Canada (AAFC), Saint-Jean-sur-Richelieu, Quebec (see

In 1959, the PRTWO began evaluating trees, shrubs, and roses in the Prairie Provinces, under the auspices of the Western Canadian Society for Horticulture (WCSH). Since that time, more than 1430 accessions have been propagated primarily from the AAFC-Morden Arboretum and distributed to cooperators at ten locations (eight active) for five-year trials of overall adaptation and plant growth. Detailed observations and notes are filed at the AAFC - Morden Arboretum. Historically, reports on plant performance were published approximately every 3 years in the report of proceedings of the WCSH. Reports are now complied periodically and mailed to interested parties, as well as being made available at

In 1983, cooperators at a wide range of sites (presently seven) in Alberta initiated a provincial evaluation program (the ARWPTP), which conducts six-year evaluations resembling those conducted by the PRTWO. Results and images of trial plants are posted at

International Registration Authorities (IRAs)

The purpose of an IRA is to promote stability in the nomenclature of cultivars and cultivar groups within designated plant groups and to produce and promote authoritative checklists and registers of all names known to have been in use in such groups. The IRA records and registers cultivar and cultivar group names, and collects information on the cultivar, including herbarium vouchers, other illustrative materials, and evaluation data. An IRA may be an individual with superior knowledge of the taxon, or may be a member of a plant society, governmental organization, botanic garden, or university. Some genera of woody ornamental landscape plants have their own registrar (e.g. boxwood, holly, and camellia), while most fall under the registration authority for unassigned woody plants. Although the IRA does not conduct trials, judge distinctness of cultivars, or judge the superiority of one cultivar over another, the organization that sponsors the IRA often does participate in evaluation of plant materials. A list of IRAs can be found on the web site of the International Society of Horticultural Science at .

Status of Woody Landscape Plant Germplasm Enhancement/Breeding Activities

Compared to other crop commodities in the United States, breeding efforts of woody landscape plants are disproportionately low, especially considering the value of woody landscape plants to the U.S. economy. A 1985 survey by Brooks and Vest identified a total of 7.7 full time scientists devoted annually to breeding and genetics of landscape trees and shrubs by scientists at publically supported institutions in the U.S., while a survey conducted in 1994 and published as the ‘National Plant Breeding Study-I' in 1996 by Iowa State University revealed that in 1994, there were 18 ornamental breeders at universities (11.7 or 65% woody); 5 ornamental breeders in ARS (4 or 80% woody); and 64 ornamental breeders in industry (23.9 or 37% woody, omitting pine). Because of the long life cycles and the high cost involved in breeding woody plants, most small nurseries cannot afford the investment to operate breeding programs. A few genera, such as the rhododendrons and roses, have hobbyist breeders; however these efforts primarily focus on breeding for large showy flowers or other aesthetic qualities and often do not involve multi-generation crossing programs to incorporate resistance to pests or tolerance to urban and other environmental stresses.

Only a few public institutions have active woody ornamental breeding programs. These include the USDA/ARS U.S. National Arboretum, the USDA/ARS site in Poplarville, MS, the University of Minnesota, the Landscape Plant Development Center, Rutgers University, Texas A&M, North Carolina State University, the University of Georgia, Mississippi State University, the University of Arkansas, and Oregon State University. Reduced support levels have resulted in many public institutions either reducing or eliminating their breeding programs. The Holden and Morton Arboreta are the only two known private arboreta or botanic gardens known to have an active breeding program in woody landscape plants. In Canada, the Morden Experiment Station is the only institution actively involved in breeding activities.

U.S. National Arboretum

The Floral and Nursery Plants Research Unit of the U.S. National Arboretum conducts a broad-based program contributing to basic and developmental research and the implementation of new technologies for the floral and nursery industries. Emphasis is placed on developing new and superior floral and woody nursery plants. In addition, the Unit has the responsibility to collect, propagate, maintain, distribute, evaluate and preserve representative levels of inherent genetic diversity of woody landscape plants as part of the NPGS.

Landscape Plant Development Center

The Landscape Plant Development Center (LPDC) is a non-profit organization with a mission of developing stress-tolerant landscape plants for all geographic regions, with emphasis on USDA Hardiness Zones 3 through 5. The LPDC's approach is a cooperative effort with research participants at many institutions and broad industry support. Through this cooperative approach, the LPDC can utilize the plant collections of participating institutions to make desired crosses. The breeding strategy is based on the hypothesis that plants in the F1 generation are usually intermediate in hardiness between the two parents and thus may not possess sufficient hardiness for the most severe climates. In succeeding generations, however, there should be some individuals equal to or exceeding the tolerance of the hardiest original parent. Thus, to efficiently test generations and to discover the best-adapted strains, F2 populations are planted at institutions located in different regions. Superior plants that are well adapted to each region can be selected from the same F2 or later-generation population for either direct landscape use or for further breeding efforts to incorporate superior aesthetic traits with the previously selected environmental tolerance.

Environmental Issues Concerning Woody Landscape Plant Germplasm

Unlike most other crop plants, woody landscape plants are used to ameliorate certain environments, and also contribute extensively to the health of both natural and man-made ecosystems. Therefore, issues such as invasiveness, bioremediation, threatened and endangered species, and erosion control are all relevant to the WLPCGC. While these issues cannot be treated extensively in this document, it is important that these issues be considered when making decisions regarding woody landscape plant priority genera, collection/exchange proposals, and curation. The National PLANTS Database (, maintained by the USDA NRCS, maintains lists of invasive as well as threatened and endangered plants.

Invasive Plants

Invasive plants have increasingly severe environmental, political and economic ramifications, and prevention of further releases of invasive or potentially invasive species should be encouraged. The WLPCGC recognizes that plant introduction and improvement are the foundation of modern horticulture, yielding a diversity of useful plants for managed landscapes and gardens, and that only a small proportion of introduced plant species become invasive and cause unwanted impacts to natural systems and biological diversity. The issue is complicated by the fact that species can be invasive in some regions, but not in others, and the impacts of invasive species can occur at times and places far removed from the site of introduction. These principles have been reiterated by several groups, including the National Invasive Species Council established by the Federal Executive Order 13112 on February 3, 1999, and the St. Louis Declaration (December, 2001).

Threatened and Endangered Species

Concerns that species and their habitats may be adversely affected by human activities have resulted in federal, state and local legislation, including the Endangered Species Act of 1973 (ESA) (16 U.S.C. 1600-1614), as amended. ESA was enacted to provide for protection of endangered plant and animal species and their habitats. ESA's provisions include the federal listing of such species as threatened or endangered, establishment of standards for their treatment, and specification of mandated actions towards recovery of listed species. Germplasm collections can serve important roles in preserving endangered plants and providing material for research and reintroduction programs. Genotypes and even species and genera that are extinct in the wild are preserved in cultivation, and some of these (such as Ginkgo biloba and Franklinia alatamaha) have proven very valuable for landscape use.

Maintenance, distribution and research on threatened germplasm are important for the nursery industry as well as for conservation purposes. The nursery industry can play a role to in the preservation and reintroduction of threatened and endangered plants. Activities on holdings of threatened and endangered species in the United States are being coordinated by the Center for Plant Conservation, and international transportation of endangered species is governed by the Convention on International Trade in Endangered Species (CITES).


The following recommendations, the priority genera lists, and this entire report are meant to be revisited each year when the WLPCGC holds its business meeting.


Before it is practical to prioritize collection and preservation needs more explicitly, a more comprehensive inventory is needed of what already exists in cultivation. Our prioritized lists (Appendix 1) are first steps in this direction. An assessment of the extent to which that inventory constitutes authentic material representative of taxa in nature must be made. Consequently, high priority should be placed on the loading of passport and inventory information on the collections of the U.S. National Arboretum into GRIN, followed by that for the collections of any other USDA facility not already in GRIN. This effort should then be extended to any other agency of the federal government holding permanent collections of woody plants. Also, a strong effort should be made to link holdings in NAPCC collections with the GRIN accession and taxonomy areas. Once this partnership is established, decisions regarding germplasm collection and preservation needs may proceed with some assurance that they will reflect national priorities.


The task of maintaining woody plant germplasm is an enormous one and unlikely to be fulfilled completely by either the NPGS or AABGA. It would therefore be highly advantageous to both organizations to coordinate efforts due to the limited resources and to avoid duplication. The coordination of germplasm preservation among different institutions will have several important benefits, including a more complete representation of the germplasm of managed taxa, without any cooperator necessarily having to increase the size of its collection; an increase in the overall efficiency in managing plant germplasm, with the opportunity to locate plants at environmentally favorable sites; less likelihood of a catastrophic loss of germplasm of managed taxa, with different clones being located at different garden sites; and more effective long-term management and easier transfer of collections when necessary.

The efforts of the AABGA to establish a consortium of botanical gardens and arboreta with the resources and willingness to manage their documented plants as one, national collection is to be commended and supported. Because of a lack of sufficient funds, this program may be jeopardized or restricted in the future. It is in the best interest of both the NPGS and AABGA that this program succeeds. Although the partnership has begun, much work remains for this collaboration to be fully realized. Specific targets include: increased support for coordination, database linkages with distributed querying, expanded institutional participation, and improved curatorial and evaluative expertise.

Because of the diversity and number of woody landscape plant genera, a coordinated approach to preservation/curation would be most effective. The U.S. National Arboretum is well-suited to take a leadership role in this responsibility, through a support position either with Plant Records or the WLPGR. Working closely with the coordinator of the NAPCC and other NPGS curators, a full-time position at the National Arboretum could focus on integration of plant databases from other gardens and training of member curators of NAPCC. Such cooperation will identify duplication in collections, assist in increasing diversity of holdings, and help optimize survival of plants more suited to one region of the country than another. The curators should continually strengthen working relationships with other federal agencies that maintain or oversee woody plant germplasm both in situ and ex situ, notably the Bureau of Land Management, the National Park Service, the U.S. Forest Service, and the Natural Resources Conservation Service, in order to coordinate the preservation of all significant collections of woody landscape plants currently under federal jurisdiction.

We endorse a pilot study headed by Rick Lewandowski to study the ease and problems associated with transferring electronic data about plant collections at various gardens, maintained on various platforms to a spreadsheet format. Initially five genera (Camellia, Viburnum, Magnolia, Cornus, Ilex) will be studied, and Rick will request specific field information from 15 institutions. It is important to document how much time it takes, results, and problems, so that a proposal can be developed to send to the National Program Staff (NPS) for future funding of a more comprehensive effort through NAPCC. It would be useful to NPS to have an estimate of the contribution of each partner in NAPCC (i.e., what resources each member institution has committed or will commit to maintain germplasm).

We recommend that GRIN nomenclature be used if there is no established synonomy (

We endorse the concept of using distributive querying of on-line plant databases as a cooperative collection management tool, and encourage GRIN staff to join a multi-disciplinary task force to adapt existing software for this purpose. It is also recommended that grant programs be established to help support NAPCC member gardens in moving their collection databases on-line.


Although the Plant Materials Program already cooperates with the NPGS, further enhancement of this relationship is possible in the following areas: preservation of NRCS collections; submission of existing collections to NPGS; funding for future collections and evaluations; and facilitation of other NRCS-NPGS collaborations.

Germplasm Preservation

While planting out and seed banking are suitable ways to maintain woody plant germplasm, given current technology and limitations in funding, other methodologies, including cryopreservation of dormant buds and seeds, appear to have merit and may prove to be more efficient in the future because of greater economies of space and labor over time. Continued research, where information is lacking, and compilation of findings on these methodologies as they related to woody plants should be encouraged.

The search for, and collection of, diverse sources of wild populations and their preservation should take precedence over cultivated material since habitat loss could result in the loss of valuable germplasm. In addition, collection and maintenance of wild populations species is the most economical method of preserving the largest number of genes in any plant group. However, we recognize that cultivated germplasm also has value, and efforts should be made to avoid the loss of germplasm when breeders discontinue working on certain lines. The collection of any species should include samples from the various extremities of its range, ecologically as well as geographically, and from various locations between the extremities. Until information becomes available that would suggest a more feasible approach, we recommend that the core collection approach be implemented with woody landscape plant germplasm preservation.

Because research on invasive plants often requires study of the invasive species themselves, we do not recommend eliminating potentially invasive plants in germplasm collections. However, we do recommend that dissemination of these species, whether through natural seed dispersal or through distribution to users by curators, be carefully controlled.

Preservation of accessions from recent and current exploration efforts have also been identified as a high priority.

In cooperation with NAPCC, encourage the development and application of best management practices in curation and attempt to address the lack of continuity in curation of specific collections.

The Glenn Dale move

The transfer of plant germplasm from Glenn Dale to Beltsville, MD represents an opportunity for evaluation and possible consolidation of the materials, but is also a major threat to valuable and unique germplasm. The curator of the WLPGR should seek advice, as needed, from members of a subcommittee of the WLPCGC that formed specifically to advise on technical and germplasm aspects relating to this undertaking. The CGC can also take partial responsibility, if necessary, for loss of plant material that occurs as a result of its recommendations. A WLPCGC subcommittee consisting of Jim Berry, Paul Capiello (chair), Harold Pellett, and Mark Widrlechner was recently established. This subcommittee should receive a list of pertinent germplasm from the curator of the WLPGR and may visit the site if necessary, with travel support from the NPS.

Germplasm Characterization

Identify unnamed plants of known wild origin and verify named plants of known origin in existing collections.

Germplasm Evaluation

Identify substantial collections within prioritized genera to determine whether evaluation programs are justified.

The WLPCGC, working with NAPCC and other interested organizations and agencies, should develop a directory of North American evaluation programs along with a summary of how results from these evaluations can be obtained.

Better cooperation between evaluation programs and institutions that are able to maintain germplasm must be encouraged. GRIN and projects such as NAPCC should act as bridges to connect evaluation data with maintenance records. All pertinent institutions and agencies need to provide adequate maintenance for accessions being tested.


Most programs are aimed at the southern half of the U.S., with much less effort to the northern U.S., tropical regions or the southwest. We recommend support for cooperation between the LPDC and the USNA breeding programs to explore the potential to strengthen breeding efforts for northern parts of the U.S., as well as support for breeding efforts that focus on tropical or arid species.

Germplasm Exploration/Exchange

Examine germplasm holdings within GRIN (and NAPCC, as the program develops), and compare with the WLPCGC priority list to identify gaps and/or voids for future exploration or exchange. Similarly, identify substantial collections within prioritized genera and identify whether exploration is justified.

Foster support of cooperative landscape plant exploration and collecting expeditions such as those initiated by NACPEC. Encourage cross-disciplinary collaboration to make efficient use of available resources. Increase awareness of grant programs among the botanical garden and arboretum community.

In making recommendations for exploration of woody plant germplasm, the WLPCGC will consider both the invasive potential of the species in question, as well as the potential benefits to U.S. horticulture. Therefore, germplasm exploration proposals submitted for endorsement by the WLPCGC must specifically address the issue of invasive species.

Germplasm Distribution

A one or two sentence "warning" should accompany woody landscape germplasm distribution from repositories or from Indices Seminum, reminding receivers of the threat of invasive species and the regional differences in invasive behavior.

Appendix I: Excel spreadsheets (one for temperate genera, one for tropical genera) with rankings and other information for genera of woody landscape plants.

Useful Web sites related to this document
Web Link Web Site The U.S. Department of Agriculture The Agricultural Research Service The U.S. Forest Service The National Resource Conservation Service The Plant Materials Center of the NRCS The National PLANTS database The U.S. National Arboretum, including the WLPGR The National Genetic Resources Program Plant Germplasm Repositories in the U.S. GRIN Taxonomy The American Society for Horticultural Science The American Nursery and Landscape Association American Forests The International Society for Horticultural Science The American Association of Botanic Gardens and Arboreta NC-7 trials Evaluation trials from the Western Canadian Society for Horticulture Canadian evaluation trials in Quebec Canadian evaluation trials in Alberta