Aggregated occurrence records of invasive European frog-bit (Hydrocharis morsus-ranae L.) across North America

Study Extent

We include all accessible North American occurrences (observation- and specimen-based) dating from 1932 to July 2021 in the dataset. The data represent occurrence records from two Canadian provinces (Ontario and Quebec) and thirteen U.S. states; ten of which have recorded EFB presence (Florida, Maine, Michigan, New Jersey, New York, Ohio, Pennsylvania, Vermont, Washington State, and Wisconsin) and three of which have recorded absence only (Illinois, Indiana, and Kentucky).

Sampling

European frog-bit occurrence records were aggregated from digital data repositories, natural history collections, and university researchers. A total of 23,985 observation-based and specimen-based digital records were initially obtained; after data validation and duplicate removal, the total aggregated dataset contains 12,037 unique records. Specimen-based data in natural history collections were accessed through digital specimen data aggregators: Consortium of Midwest Herbaria, Global Biodiversity Information Facility, Great Lakes Invasives Network, and Integrated Digitized Biocollections.

Quality Control

Field names and contents of raw data were standardized to ensure consistent capitalization, spelling, grammar, taxon naming conventions, and formatting to conform to Darwin Core standards, as described in the Darwin Core Quick Reference Guide. We identified and consolidated duplicate observation-based records held by multiple online repositories, retaining all record numbers to ensure each merged record would be traceable to every online source that houses it. We merged specimen-based records only when they were taken from the same specimen sheet (as verified by examining each original specimen image) or associated with an observation-based record. When specimens were known to be physical duplicates (separate individuals collected by same collector at same time and place) or when images were not available, specimen-based records were retained. We standardized information in the eventDate and eventTime fields to conform to ISO 8601-1:2019 and recorded original dates in the verbatimEventDate field, as per Darwin Core standards. Occurrences recorded with dates on January 1 were inconsistent with the known phenology of EFB in its invasive range. For these records, only the record year was retained. One hundred fifty digitized specimen images were provided by Agriculture and Agri-Food Canada's National Collection of Vascular Plants. Image labels were transcribed to Darwin Core fields. They include data as early as 1936, in the first few years of EFB's invasive spread following its 1932 introduction. Data were corrected and modified only to the extent necessary to improve clarity and usability; original content was maintained whenever possible. When locality strings were updated using associated data or linked records, original locality strings were retained in verbatimLocality, as per Darwin Core standards. We corrected specimen sheet transcriptions and reference URLs where needed. When provided, original geographic coordinates were retained. When no coordinates of any kind were available (290 records), we georeferenced records using the GEOLocate Web Application and following the guidance of Chapman and Wieczorek (2020). We noted decisions regarding placement of coordinate points and their associated uncertainty in locationRemarks and georeferenceRemarks. Seven records could not be georeferenced due to localities that were too broad or indeterminate, and we noted this in georeferenceRemarks.

Method steps

1. See Quality Control

1. Hydrocharis morsus-ranae L.
   common name: European frog-bit rank: species

30.3207 and 49.7652 Latitude; -121.9681 and -69.8762 Longitude