CPC Best Plant Conservation Practices

to Support Species Survival in the Wild

Key Messages About Collecting Seeds
  • Species characteristics, legal parameters, and the purpose of the collection influence decisions about timing, locations, and numbers of seeds (or other tissues) that will need to be collected.
  • Ethics of doing no harm to the wild rare plant population guide actions in the field.
  • The intention of capturing representative genetic diversity guides the number of individuals and number of populations to target for collection.
  • Careful documentation is essential for maximizing the value of the conservation collection.

The Purpose of Conservation Seed Collections

The primary purpose of a conservation collection is to support species’ survival and reduce the extinction risk of globally and/or regionally rare species. A conservation collection is an ex situ (off-site) collection of seeds, plant tissues, or whole plants that has accurate records of provenance, differentiated maternal lines, and diverse genetic representation of a species’ wild populations. To be most useful for species survival in the wild, a conservation collection should have depth, meaning that it contains seeds, tissues, or whole plants of at least 50 unrelated mother plants from each population, and breadth, meaning that it consists of accessions from multiple populations across the range of the species. Conservation collections of seeds should have initial germination and viability testing, developed cultivation protocols, and periodic long-term viability testing.

Prioritizing species, populations, and regions for ex situ collecting: Threatened native U.S. oaks as a case study

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Questions to Ask Before Acquiring a Conservation Collection
  1. Does collecting pose a threat to the wild population?
  2. What is the purpose of the collection? Note: These guidelines pertain to conservation collections. Depending on the purpose of the collection, sampling strategy and numbers can vary (Guerrant and Fiedler 2004; Guerrant et al. 2004).
  3. Can the ex situ collection be made such that it benefits the species’ survival and reduces extinction risk?
  4. How many estimated or known numbers of individuals and populations exist? (The sampling universe is known.)
  5. What is the breeding system?
  6. Is the taxon monoecious or dioecious?
  7. Is it self-compatible or self-incompatible?
  8. What is the propagule dispersal mechanism?
  9. In what types of habitats does the species grow?
  10. Should seeds or other tissues be collected? (See “Questions to Ask to Determine the Most Efficient Way to Preserve the Plant Tissue Long-Term.”)
  11. What is the storage capability of the taxon? Can the seeds be stored in a seed bank or will the other forms of ex situ specialized propagation and care be required?
  12. How long will material be stored?
  13. How can the plant material be propagated? Do you know the horticulture requirements for growing plants from seeds or cuttings?
  14. What level of attrition or mortality of collected material is expected in storage and regeneration? (See Guerrant and Fiedler 2004).
  15. Will the material be used for a reintroduction or conservation translocation?

Make preparations before making collections.

  • See “Questions to Ask before Acquiring a Conservation  Collection” chart (above) and “Questions to Ask to Determine the Most Efficient Way to Preserve the Plant Tissue Long-Term” chart (below).
  • Know how to identify the species and know its natural and cultural history. Consult with local botanical experts and agency recovery staff. Work with in-country partners to make collections. By acquiring data on the species’ phenology at the target population site, you may streamline your collection trips. Visit publicly available plant collections databases, such as the Global Biodiversity Information Facility (GBIF), to determine the time of year a species typically produces flowers or fruits. Explore citizen science projects, such as iNaturalist, to view georeferenced photos of plant observations in real time. Take a reconnaissance trip to verify the actual timing of flowering and fruit set so that you can capture seeds when they are ripe. Recording flowering date and maturity of seeds in the population can aid future collections and can be reported with accession information. (See Example Monitoring Form.)
  • Understand legal obligations for collection, transport, and propagation. Obtain permission from landowners to make seed collections and report permit numbers in accession records. Realize that obtaining permits for listed species may require obtaining permits from landowners and regulatory state and federal agencies; the process may take as long as 6 months to 1 year, so it is important to begin the process well in advance of your collecting season. FAQ – How can I obtain permits to make seed collections?
  • Know sources for gathering reliable information about species’ conservation status. FAQ – How can I find out a species conservation status?
  • Research the seed storage requirements of a taxon, as this will determine how the seed will need to be processed after collection. FAQ – How do I know my species storage requirements?
  • To avoid over collection and/or to learn from other collectors, survey other ex situ collections to determine what species and populations have already been collected. For example, check records in Plant Search for Botanic Gardens Conservation International or California Plant Rescue.
  • Search for ex-situ collection status of priority species using CPC’s Rare Plant Finder
  • Become familiar with Sentinel Plant Network and Weed Risk Assessments.
  • Evaluate potential pest/pathogen issues and invasive behavior of the species you are collecting (Gordon and Gantz 2008; Gordon et al. 2008a and 2008b; Reichard et al. 2012).

Adopting a Cinderella Ecosystem: A Tale from the Great Plains

James Locklear, Lauritzen Gardens While our plant conservation work is primarily focused on individual at-risk species, Lauritzen Gardens has taken on an unanticipated role as authority... Read More
Questions to Ask To Determine the Most Efficient Way to Preserve the Plant Tissue Long-Term

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While collecting, do no harm to collecting site or the rare plant population.

  • If no previous specimen exists for the species at your collecting site or if the last known specimen is more than 10 years old and the population is large enough to accommodate removing one plant or plant part, document the identification of the species with a voucher specimen. If the population is not large enough, take good photographs. Note that permission to collect the voucher may be required prior to the collection.
  • Collect within permit guidelines. To minimize impact on the wild population, collect no more than 10% (or the maximum allowed by permits) of an individual plant’s reproductive output and/or no more than 10% of the population reproductive output in a season (Menges et al. 2004). For many species making collections at this intensity can be sustainable over multiple years, but the intensity and frequency of safe collection is influenced by populationand climate specifics. (See the “10% Rule” box below and CPC Best Practice Section,  “Acquiring a Conservation  Collection”)
  • Adhere to highest outdoor standards. Leave only footprints. Some habitats are extremely fragile. Adjust actions accordingly, including being mindful of habitats that are particularly sensitive to trampling and erosion.
  • Be aware of any sensitive animal species at your sites. Access may require permits, training, or adjusted timelines if protected animal species co-occur with or near your species of interest.

Special considerations in the seed collections of two NC rare plant species

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10 Percent Rule

How many seeds should I collect in a year?

CPC recommends collecting no more than 10% of an individual or population seed production in one season.


Flexible Seed Harvest: Revisiting the 10% Rule

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How many years can I collect from the same population without doing harm?

CPC recommends collecting no more than 10% of an individual or population seed production in one season and no more than 10 out of 90 years.

The research that supports this recommendation is derived from Menges et al. (2004). Note that it is important to know some aspects of the species population demography, life history, and the initial population size to determine whether your population could be impacted by harvesting 10% of its seed crop in multiple years. If you have enough data, it is possible to generate models to examine the sensitivity of population growth to reduction in fecundity caused by seed harvest. In the absence of this data, realize that generally a population with fewer than 50 individuals will have a higher extinction risk than larger populations. Species that depend on annual fecundity would be most sensitive to harvest. These would be short-lived species (especially annuals) that don’t store seeds in a persistent seed bank (Figure 1.1).

Menges et al. (2004) used theoretical modeling in which they categorized 22 species (25 populations with published demographic data) into three types: Extinction Prone, Sensitive I (high initial extinction risk), Sensitive II (low initial extinction risk), and Insensitive. Insensitive species, nine species with populations with 50 or more individuals, could withstand any intensity of harvest over 100 years and had no extinction risk. The insensitive species they modeled were: Ardisia escallonioides, Calochortus obispoensis, Erythronium elegans, Neodypsis decaryi, Pedicularis furbishiae at Hamlin, Primula vulgaris, Themeda triandra, and Thrinax radiata. Note that these species are trees, shrubs, and iteroparous herbaceous perennials. Species categorized as extinction prone had 100% extinction probability with or without seed harvests. They included: Arabis fecunda, Ariseaema triphyllum, Eupatorium perfoliatum, and Pedicularis furbishiae at St. Francis. The Sensitive I species (Danthonia sericea and Eupatorium resinosum) were iteroparous herbs with clonal growth that had high extinction risk >40% without seed harvest and increased extinction risk with seed harvest above 10% in 50% of the years, while Sensitive II species (Arabis fecunda, Astragalus scaphoides, Calathea ovandensis, Dipsacus sylvestris, Fumana procumbens, Heteropogon contortus, Horkelia congesta, Pana quinquefolium, Pedicularis furbishiae, and Silene regia) had initially low extinction risk that increased with seed harvest frequency and intensity at levels above 10% harvest in over 10% of years. Frequent low-intensity harvests produced models with lower extinction risk than infrequent high-intensity harvests.

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Figure 1.3 – Extinction percentages by sensitivity class for initial population size of 50. Models conducted with 25 populations of 22 total species. Note 19 of 25 populations can withstand harvest of 10% of seeds in 10 of 90 years.

Capture representative genetic diversity.

  • Capture representative genetic diversity across the population’s spatial expanse and diversity of morphology and seed appearance. Include seeds from large and small maternal plants, along the edge and from the center of the population. It is also good to sample across years to capture diversity.
  • Strive to collect mature seeds.
    • Wild populations will almost invariably have seeds at different stages of maturity. If possible, visit a single site multiple times to collect mature seeds on several dates during the fruiting period. However, if only one harvest is possible (perhaps because a site is remote), collectors should sample representatively. A sample containing more than 10% immature seed must be processed expeditiously and should be targeted for cryogenic storage.
    • If possible, collect parallel leaf samples for DNA banking while making seed collections.

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Plan your sampling strategy for the collection.

  • Use population size and fecundity to plan your sampling strategy for the collection.
  • An ideal collection would have 3000 seeds from 50 maternal plants for each FAQ: Why should I try to collect 3000 seeds?
  • Ideal is not always reality. Some populations are simply too small to produce 3000 seeds in a season—or even across multiple years. For the rarest taxa, collecting fewer than 100 seeds may be the only option. If you cannot collect 3000 seeds or seeds from 50 maternal plants, collect no more than 10% of the seed output of a population in a season. Do the best you can.
  • Realize that extremely small seed collections (<100 seeds) will require making additional collections in the future. Plan to make additional collections. If more than 300 seeds cannot be collected within 5 years, to increase quantities of seeds in storage, try a seed increase rather than wild collection. See CPC Best Practice Section “Curating Small Samples: Increasing the Number of Seeds for Storage and Restoration” if it is unlikely that a collection can ever surpass 100 seeds or 300 seeds in 5 years.
  • Strive to collect from 50 maternal plants. (See CPC Best Practice Chapter “Genetic Guidelines for Acquiring, Maintaining, and Using a Conservation  Collection;” Bureau of Land Management 2016). FAQ: Why should I try to collect seed from 50 maternal  plants?
  • If a population has fewer than 100 individuals and maternal plants produce small numbers of seed, attempt to capture up to 10% of the seeds from each of the reproductive individuals. For larger populations, subsamples are sufficient (see Figure 3.1).
  • It is always better to collect and maintain maternal lines because it gives options to equalize family lines in reintroductions and may add value to potential projects down the line or a use unanticipated at the time of collection. If your species has individuals that produce fewer than 20 seeds, so that collecting 10% of a maternal line equals one or two seeds, it may be appropriate to bulk the collection, maintaining an equal number of seeds collected from each mother plant.

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Collecting herbarium vouchers with seed collections helps document the identity of the collection longterm. Matt Lobdell is pictured collecting Magnolia ashei at Torreya State Park Photo credit: Greg Paige.

Seek to capture at least five populations.

  • If they exist, seek to capture at least five populations of a species, across space and time (Falk and Holsinger 1991). (See CPC Best Practice Chapter “Genetic Guidelines for Acquiring, Maintaining, and Using a Conservation Collection”)
  • If it is a widespread species, collect from populations across the distribution and capture each ecoregion.
  • If it is narrowly distributed, collect from as many populations as possible.

Document the collection appropriately.

  • Essential accession information includes: institution name, accession number, collector, collection date, species name, family, locality information, georeferenced latitude and longitude, site ownership, permit documentation, and population information (the total number of individuals in the population, number of reproductive individuals, and number of individuals sampled for seeds that were harvested). (See Example Field Collection Form from California Botanic Garden.)
    • Providing habitat information may provide clues to germination or tissue culture requirements of the species. Recommended fields include light and moisture conditions, soil type, slope orientation, and associated species. Provide photos of the habitat and the plant in its habitat.
    • Be sure to document any associated collections (for example, leaf litter, soil, mycorrhizal fungi) and maintain the link through processing of samples.
    • Gather and report additional accession data according to their institutional protocols. Complying with International Transfer Format for Botanic Garden Plant Records and/or Darwin Core standards will allow easy transfer of information to partners.
    • Complete one field form per accession. Multiple accession numbers and field forms only need to be created for collections made from populations, which are separated by at least 1 kilometer.
    • Transmit accession data to CPC and ARS-USDA National Laboratory for Genetic Resources Preservation (NLGRP) via online form provided to Participating Institutions through the CPC Resources section of this site. The electronic accession form can be found under the “NLGRP Submission” tab.
Determining Storage Requirements

Several authors have examined patterns in seed storage behavior (see references) that can help collectors. Begin with a literature review to check if any previous research has been done on your taxon. You can check congeners, but beware that this is not always reliable or conclusive. Our Hawaiian colleagues have found quite varying storage behavior within a single genus (Walters, Weisenberger and Clark, personal communications). Many factors determine variation in seed tolerance to desiccation or freezing. The following are some general patterns observed in seeds that tend to withstand orthodox storage or not.

Trait Likely to Be Orthodox
(Desiccation and Freezing Tolerant)
Questionable Tolerance to Orthodox Storage
Habitat Arid is especially likely; If it is not growing in a wetland, it is likely Wetland, riparian
Conditions in nature Seeds normally experience dry down and/or hard freezes Seeds normally remain moist and do not experience hard freezes
Season of seed production Not spring Spring
Life form Not tree tree
Seed bank Persistent Not persistent
Dormancy With dormancy No dormancy
Seed moisture content at time of maturation Dry when it is naturally shed from plant High (30%–70%)
Seed size Very large (avocado seeds aren't desiccation tolerant) or very small (orchid seeds and fern spores require storage in liquid nitrogen)
Plant Groups with High Proportion of Desiccation Sensitive Seeds Plant Groups with Predominantly Orthodox Seeds
ANITAGrade Arecales Ericales Fagales Icacinales Laurales Magnoliales Malpighiales Myrtales Orchidaceae Oxalidales Santalales Salicaceae Sapindale Solanaceae Poaceae Asteraceae Brassicaceae
GPS Clippers Marker
Notebook Tweezers
Collecting envelopes (coin envelopes or glassine envelopes)
Paper bags
Camera Glue sticks or tape to seal envelopes
Flagging to mark individuals in the field

International Standards

Reference for CPC Guidelines
FAO Genebank Standards for Plant Genetic Diversity (FAO 2014)
Standards for Acquisition of Germplasm
4.1.1 All seed samples added to the genebank collection have been acquired legally with relevant technical documentation.
4.1.2 Seed collecting should be made as close as possible to the time of maturation and prior to natural seed dispersal, avoiding potential genetic contamination, to ensure maximum seed quality.
4.1.3 To maximize seed quality, the period between seed collecting and transfer to a controlled drying environment should be within 3 to 5 days or as short as possible, bearing in mind that seeds should not be exposed to high temperatures and intense light and that some species may have immature seeds that require time after harvest to achieve embryo maturation.
4.1.4 All seed samples should be accompanied by at least a minimum of associated data as detailed in the FAO/Bioversity multi-crop passport descriptors.
4.1.5 The minimum number of plants from which seeds should be collected is between 30-60 plants, depending on the breeding system of the target species.
MSB Partnership Collections (Millennium Seed Bank Partnership 2015)
Seed, herbarium vouchers, and data are collected to recognized protocols or guidelines:
1.1 Genetic materials, including traditional knowledge, are legally collected and conserved.
1.2 Collection names are verified (ideally by reference to herbarium voucher specimen).
1.3 Genetic diversity of sampled population is adequately represented.
1.4 Essential field data is recorded.
1.5 Survival of source population is not compromised.

Baskin, C. M., and J. M. Baskin. 2014. Seeds: ecology, biogeography, and evolution of dormancy and germination. 2nd ed. Academic Press, San Diego.

Brown, A. D. H., and D. R. Marshall. 1995. A basic sampling strategy: theory and practice. Collecting plant genetic diversity: technical guidelines. CABI, Wallingford, UK: 75–91.

Bureau of Land Management. 2016. Technical protocol for the collection, study, and conservation of seeds from native plant species for Seeds of Success.

Falk, D. A., and K. E. Holsinger. 1991. Genetics and conservation of rare plants. New York, Oxford University Press.

Food and Agriculture Organization of the United Nations (FAO). 2014. Genebank standards for plant genetic resources for food and agriculture. Rome, Italy. http://www.fao.org/3/a-i3704e.pdf.

Gordon, D., and C. Gantz. 2008. Screening new plant introductions for potential invasiveness: a test of impacts for the United States. Conservation Letters 1:227–235.

Gordon, D. R., D. A. Onderdonk, A. M. Fox, and R. K. Stocker. 2008a. Consistent accuracy of the Australian weed risk assessment system across varied geographies. Diversity and Distribution 14:234–242.

Gordon, D. R, D. A. Onderdonk, A. M. Fox, R. K. Stocker, and C. Gantz. 2008b. Predicting invasive plants in Florida using the Australian weed risk assessment. Invasive Plant Science and Management 1:176–195.

Griffth, M.P., M. Calonje, A. W. Meerow, F. Tut, A.T. Kramer, A. Hird, T.M. Magellan, and C.E. Husby. 2015. Can a botanic garden cycad collection capture the genetic diversity in awild population. Int. J. Plant Science 176: 1-10.

Guerrant, E. O., Jr., and P. L. Fiedler. 2004. Accounting for sample decline during ex situ storage and reintroduction. Pages 365–385 in E. O. Guerrant, Jr., K. Havens, and M. Maunder, editors. Ex situ plant conservation: supporting species survival in the wild. Island Press, Washington, DC.

Guerrant, E. O., Jr., K. Havens, and M. Maunder, editors. 2004. Ex situ plant conservation: supporting species survival in the wild. Island Press, Washington, DC.

Millennium Seed Bank Partnership (MSB). 2015. Seed conservation standards for “MSB Partnership Collections.” Royal Botanic Gardens, Kew, UK.

Reichard, S., H. Liu, and C. Husby. 2012. Is managed relocation of rare plants another pathway for biological invasions? In J. Maschinski and K. E. Haskins, editors. Plant reintroduction in a changing climate: promises and perils. Island Press, Washington, DC.

Seed Conservation Hub. Accessed August 3, 2017..

Volk, G. M., D. R. Lockwood, and C. M. Richards. 2007. Wild plant sampling strategies: the roles of ecology and evolution. In Plant breeding reviews, volume 29. John Wiley and Sons, Inc., New York, New York.

Wieland, G. D. 1995. Guidelines for the management of orthodox seeds. Center for Plant Conservation, St. Louis.

Wyse, S. V., and J. B. Dickie. 2016. Predicting the global incidence of seed desiccation sensitivity. Journal of Ecology. doi: 10.1111/1365-2745.12725.

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