Illinois Natural History Survey - University of Illinois

****Under Construction****

Please note that due to the rapid pace of progress and frequent additions to the Illinois Plants website, this page is currently in the process of being updated with new information, in addition to undergoing general editing. Thanks for your patience while this page is being updated. (gs 2/17)


 About the Data and Databases

Interpretation of data quality is the responsibility of the data-user.  We recognize that there are errors and omissions within our database.  We rely on your help to correct those errors and to use the data with necessary caution.  We provide detailed information about the data sources below


Species Distribution & Occurrence Records: 

Species occurrence records were obtained from herbarium records, professional surveys, and an older treatment of the Illinois flora (Mohlenbrock & Ladd 1978).  The latter is only used to populate county-level maps of Illinois plants, as this is their scale of the reference. Sources for the plant distribution/occurrence records used to create statewide Illinois Plants county maps and location records each have specific assumptions, limitations, and strengths. The goal of Illinois Plants the plant mapping function is to provide as complete of location information as possible, while also maintaining a high level of accuracy (e.g., avoiding erroneous records).  Balancing these goals means that we are attempting to incorporate as much plant data as possible to get a complete record of each plant’s distribution, but the more records that are incorporated, the greater the number or errors that may arise where accuracy and confidence in records may be lower. 

County-level maps

We provide county-level mapping of occurrence records, where Illinois counties are shaded as follows: 

Absent: no recorded occurrence; not known from county

Medium confidence: historical accounts, mostly from Mohlenbrock & Ladd 1978.  These records have served as a key source of biogeographic information for Illinois plants for nearly 40 years.  These county-level records are unvouchered and are out of date for plants with rapidly changing distributions (such as invasive plants). Other records here are of unverifiable certainty.

Medium-high confidence:  Professional surveys that are unvouchered observations.  These surveys were typically performed by skilled botanists. Location information should be accurate.

High confidence:  Often vouchered herbarium records.  These records are linked to institution names and accession numbers that are represented by physical specimens (i.e. pressed or preserved plants in an herbarium or museum collection).  We have included curated georeferenced plant photographs from the PhytoImages website in this category.  While the taxonomy of vouchered records is the most verifiable and probably the most accurate, the quality of the geographic locations of these records is more variable.  The older records typically only include county-level locality information.  

Planted / introduced: Species that are otherwise native to Illinois but which may be introduced to a specific county or region of the state. Or they may extirpated from a county and since re-introduced into planted locations within county (e.g., restorations) where they were never historically present.  In time many of these distinctions may become less apparent and relevant. For example, as species ranges shift due to global climate change or even naturally (e.g., Cynachum laeve), or as restored and planted populations intermix with native ones.  Common examples include trees planted outside of their historic range (Taxodium distichium, Liquidambar styraciflua).


Detailed maps

We provide detailed maps that display occurrence records against a Google map of Illinois.  The mapping can be focused to particular data sources, botanists, or observation years. 


Because of concerns of data donors, we have obscured the exact location of dots for some records, usually by between 500-2000m.  When this is the case, it is noted in the downloadable file that shows the details of each occurrence record.  Therefore, different data sources have different potential errors associated with them. Some records are associated with an exact plant location and GPS reading, (e.g., ILL herbarium records). Other are associated with a habitat or natural area, in which case the dot location is typically the center of the GIS polygon, or the parking lot for park entrances. Other locations are a point within in a sample plot.


Data sources (updated 2/2017)



Specimens Vouchered

Geographic accuracy








Critical Trends Assessment Program INHS


50 m





Illinois Natural Areas Inventory Update beginning IDNR/INHS


500m - 1200 m depending on the region & landowner





Illinois Natural Areas Inventory IDNR/INHS


100m - 500m

point is from habitat polygon centroid





Illinois Department of Transportation Wetland Surveys IDOT/INHS


100 m - 500 m point is from habitat polygon centroid

1989 - 2015




Illinois Natural History Survey Herbarium INHS















PhytoImages SIU







Mohlenbrock & Ladd 1978






 Forest Preserve Dist. Will County  Various  Some  200m -500m

point is from habitat centroid or preserve entrance

 1969-2015  17,500  --


IDNR Heritage Threatened & Endangered Species Database









For species-level and intraspecific names, we mostly followed ITIS accepted names.  ITIS names were not followed in cases where recent taxonomic revisions updated ITIS concepts.  In a few cases where other names have a special status in Illinois (such as with Threatened and Endangered Species), we included those names even if they do not follow ITIS standards.  Higher level taxonomy on the site follows the Flora of North America.  When conflict or disagreement over species concepts exist, we attempt to include all concepts by way of listing synonyms.



Images and their metadata are handled via PhytoImages, a virtual herbarium that associates plant images with metadata.  Most photos were taken in Illinois by various photographers recognized in the photo’s metadata and used with their permission.  Information about using photographs is available at copyrights and via PhytoImages. Note that the web curators cannot verify all species identifications, so species identification for some images are left to the photographer, so USERS MUST NOT ASSUME THAT EVERY SPECIES PHOTOGRAPH HAS BEEN CORRECTLY IDENTIFIED.


Trait and Habitat Information:

Plant trait information originated from the Illinois Plant Information Network ILPIN and is detailed in Iverson et al. 1997.  Information for the ca. 200 plants not included in ILPIN (either because of taxonomy changes, novel records, or introductions) was added by the site authors.  Only some records have been updated to correct errors and omissions.  


Flowering Phenology:

Flowering or bloom period months for Illinois are mainly taken from Mohlenbrock 2014, when available. The remaining species are from the Flora of North America, Missouri Botanic Garden.Plant Finder website (mainly for horticultural species), and Silvics of North America for some trees.

In the future we hope to iincorporate more precise blooming dates from Swink and Wilhelm 1994, Wilhelm and Rericha 2017 or the Chicago Region.


Coefficients of Conservatism (C-values):

Coefficients of Conservatism are assigned to each plant species in a region based on the species sensitivity to anthropogenic disturbance and its likelihood of being found in high-quality native habitat remnants, i.e., natural areas that are biologically undegraded. These species values may be used to calculate an areas Floristic Quality, which is the degree to which its plant assemblage is intact and resembles that of a remnant, native habitat, which is again dependent on how much human disturbance and stress the area has accrued over time and how many of its sensitive, Conservative species  remain (high C-value, e.g., C=10). Floristic Quality is measured by calculated metrics; the FQI and/or Mean C value for an area. These metrics are calculated from the C-values of the species in a given area.

Note that in the IL Plants website and database we are still inputting species C-values, so some values are blank. Most blank values occur where a species name has changed or been updated, or differs across the Illinois or Chicago Region value.

Note also that the Chicago Region originally had values assigned to it, but as of 1997 values were assigned to all of Illinois. So for the counties where Chicago and Illinois overlap, users may use either set of values. However, one cannot mix species values across a region. This mean that values are relative to the region they were assigned ONLY. Thus, Chicago area users may choose to use either Illinois or Chicago values, but they cannot use both. And, Chicago area values MAY NOT BE USED outside of the Chicago Region.


For the Chicago region, species values are taken from:

  • Swink, F. & Wilhelm, G. (1994) Plants of the Chicago Region. Indiana Academy of Science, Indianapolis, IN.  Values available here.

 For the entire state, species scores are taken from:

  • Taft, J.B., Wilhelm, G., Ladd, D. & Masters, L.A. (1997) Floristic Quality Assessment for vegetation in Illinois, a method for assessing vegetation integrity. Erigenia, 15, 1–24. Available here.

 For further reading on species C-values and Floristic Quality in Illinois, users are referred to the following:

  • Spyreas, G. 2016. Scale and Sampling effects on Floristic Quality. PLoS One 11(8) (download)
  • Matthews, J.W., Spyreas, G. and Long, C.M. 2015. A null model test of Floristic Quality Assessment: Are plant species’ Coefficients of Conservatism valid? Ecological Indicators. 52: 1–7 (PDF) (Science Direct)
  • Spyreas, G., Meiners, S., Matthews, J.W., and Molano-Flores, B. 2012. Successional trends in Floristic Quality. Journal of Applied Ecology 49(2): 339-348 (PDF) (WIley)