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Plant species cannot be listed as endangered or threatened until scientists have done a conservation assessment. They use data, such as population numbers and habitat size, to determine a species’ risk of extinction. Conservation assessments take time and significant scientific research.

Very little of the world’s flora has been fully studied, and time is running out! Many species are losing their habitats faster than scientists can measure them. But conservationists around the world are seeking methods to quickly and accurately evaluate the species that are most in danger.

Conservation Assessment Project

How do we determine which species are endangered?

Gary Krupnick reviewing a preserved botanical specimenI am Gary Krupnick and I work in the Botany Department at the National Museum of Natural History. Here at the Museum, we devised a method to speed things up. Scientists like me work with the Museum's collection of five million herbarium specimens to decide if a species is potentially at risk and needs immediate study — before it is lost forever.

We spent four years researching our collections and learned what information would best predict a species' level of risk. We developed the flowchart you see below to sort through the thousands of species not yet assessed much more quickly than ever before.

Let me show you how we do it.


All specimens of this species collected before 1900?



No No


Collected from six or more native locations?



No No


Fewer specimens of this species than the average number of specimens for the plant family?



No No


Fewer Specimens of this species than the average number for the plant family collected after 1960?






Fig. 1 (for more information, see Krupnick, G.A., W.J. Kress, and W.L. Wagner. 2008. Biodiversity and Conservation 18(6): 1459-1474)

We developed a method to determine whether a botanical species is likely threatened, extinct, or not threatened. This method applies a series of questions that we ask about the species. Depending on the answers to each step of inquiry, we can determine the species' likely condition. The method is illustrated in Fig. 1.

Applying Our Method

We confirmed that our method worked by applying it to several endangered species known to be threatened. The IUCN lists the cactus Echinocactus grusonii as Critically Endangered. Would our method categorize this species as threatened?

illustration of Cactus species Echinocactus Grusonii

Echinocactus grusonii

  1. Were all the specimens of this cactus collected before 1900?

    The two specimens in the Museum were collected in 1906 and 1919.


  2. Are the specimens from six or more of this cactus’s native locations?

    We only have two specimens of this species, both collected from the same location.


  3. Are there fewer specimens of this species than the average number for the Cactus family?

    There are only two specimens of this species. We have, on average, five specimens per species in the Cactus family.


It worked! Our method predicts this species is likely threatened and in need of further assessment in the field—the right decision for a species already known to be endangered.

Try it Yourself

Illustration of plant species Lycast macrophylla
Lycaste macrophylla

The orchid Lycaste macrophylla has not been evaluated in the field. Try to answer the questions in the flowchart (Fig. 1) using the information below to find the answers.

Here are conditions for Lycaste macrophylla:

  • The Herbarium's five specimens were collected in three different locations in 1886, 1890, 1925, 1949, and 1950.
  • On average, we have two specimens per Orchid species in our collection.
  • On average, we have one specimen collected after 1960 per Orchid species in our collection.

Answer (don't look until you've tested our method!):

Based on the test, you should have discovered that this orchid species is likely threatened and needs further assessment in the field.

Meet Gary Krupnick, head of the Museum's Plant Conservation Unit.

Gary Krupnick, head of the Museum's Plant Conservation Unit, studying a botanical collection and taking notes.

“As head of the Museum's Plant Conservation Unit, my job is to explore ways in which data from herbarium specimens can be used in assessing the conservation status of plant species.”

Learn more about Gary

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