When to use this API
When you need authoritative taxonomic data — scientific names, common names, nomenclatural status, synonym lists, or full taxonomic hierarchy — for any organism in the ITIS database. ITIS is the taxonomic standard used by US federal agencies, and it is one of the few places where you can ask "is this scientific name still accepted?" and get a documented answer with a reason code. For phylogenetic trees, DNA sequences, or ecological observations, look elsewhere; this is nomenclature and classification, not genomics or natural history.
Looking up a species by its Taxonomic Serial Number
"What is the full taxonomic classification of the axolotl?" The Taxonomic Serial Number (TSN) is ITIS's primary key — every named taxon gets one, and a tsn: query returns the complete record in one call. No auth. No key. The axolotl (TSN 586244) makes a good first example because its record carries 19 historical synonyms, multilingual common names, and a full Kingdom-to-Species hierarchy, all in a single response.
curl "https://services.itis.gov/?q=tsn:586244&wt=json&rows=5&fl=tsn,nameWInd,usage,kingdom,rank,taxonAuthor,hierarchySoFarWRanks,synonyms,vernacular" | head -c 10000
{
"response": {
"numFound": 1,
"docs": [{
"tsn": "586244",
"nameWInd": "Ambystoma mexicanum",
"usage": "valid",
"kingdom": "Animalia",
"rank": "Species",
"taxonAuthor": "(Shaw and Nodder, 1798)",
"hierarchySoFarWRanks": [
"586244:$Kingdom:Animalia$Subkingdom:Bilateria$Infrakingdom:Deuterostomia$Phylum:Chordata$Subphylum:Vertebrata$Infraphylum:Gnathostomata$Superclass:Tetrapoda$Class:Amphibia$Order:Caudata$Family:Ambystomatidae$Genus:Ambystoma$Species:Ambystoma mexicanum$"
],
"synonyms": [
"586244:$Gyrinus mexicanus$Siren pisciformis$Triton mexicanus$Siredon axolotl$Axolotus pisciformis$..."
],
"vernacular": [
"$Axolotl$English$N$78229$2005-04-25 00:00:00$",
"$Salamandra ajolote$Spanish$N$79484$2003-01-08 00:00:00$"
]
}]
}
}
The axolotl has 19 synonyms — names given by different taxonomists across two centuries before the current one settled. Siredon axolotl is the origin of the word "axolotl" in formal taxonomy; Nahuatl speakers called it axolotl long before Shaw and Nodder described it in 1798. The hierarchySoFarWRanks field packs the full classification into a single $-delimited string — parse on $ to extract each Rank:Name pair. The vernacular field uses the same delimiter: common name, language, and metadata are separated by dollar signs.
The axolotl (Ambystoma mexicanum) is a species in the order Caudata, family Ambystomatidae, described by Shaw and Nodder in 1798. Its full classification runs from Kingdom Animalia through Phylum Chordata, Class Amphibia, Order Caudata, Family Ambystomatidae, to Genus Ambystoma. It is known as "axolotl" in English and "salamandra ajolote" in Spanish.
Checking whether a name is taxonomically accepted
"Is the variety name Agave americana var. expansa still valid?" Not every name in ITIS is currently accepted. The usage field tells you: "valid" or "accepted" means the name is current; "not accepted" means it has been superseded. For deprecated names, acceptedTSN points to the replacement and unacceptReason explains why.
curl "https://services.itis.gov/?q=tsn:182662&wt=json&rows=5&fl=tsn,nameWInd,usage,unacceptReason,acceptedTSN,kingdom,rank,comment" | head -c 10000
{
"response": {
"numFound": 1,
"docs": [{
"tsn": "182662",
"nameWInd": "Agave americana ssp. americana var. expansa",
"usage": "not accepted",
"unacceptReason": "other, see comments",
"acceptedTSN": ["566578"],
"kingdom": "Plantae",
"rank": "Variety",
"comment": [
"$21180$Jenny K. Archibald$Under ICBN Article 24.1, \"The name of an infraspecific taxon is a combination of the name of a species and an infraspecific epithet...\" taxa \"may also be referred to\" with intervening epithets (\"quadrinomials\" and such), but that while these do serve to present classification information, they are not \"names\" in the sense of the Code$2011-02-04 14:50:36$2025-12-18 00:00:00$"
]
}]
}
}
This record is not accepted because the name is a "quadrinomial" — it includes both a subspecies and a variety epithet. Under the International Code of Botanical Nomenclature Article 24.1, only the terminal epithet plus a connecting term is formally valid; the intervening subspecies epithet is classification information, not part of the name itself. ITIS flags this with unacceptReason: "other, see comments" and points to TSN 566578 as the accepted name. The acceptedTSN field is your navigation link — follow it to the current name.
The name "Agave americana ssp. americana var. expansa" is not accepted in ITIS. Under ICBN Article 24.1, quadrinomial names (with both a subspecies and variety epithet) are not formally valid — only the terminal epithet counts as a name. The accepted TSN is 566578.
Finding taxa by kingdom and nomenclatural status
"How many fungal species are listed as not accepted in ITIS?" The Solr q parameter accepts compound queries with AND. Combine kingdom, rank, and usage to narrow to any slice of the taxonomy. The numFound field in the response gives the total count without fetching all records — use it for "how many" questions before paginating.
curl 'https://services.itis.gov/?q=kingdom:Fungi+AND+rank:Species+AND+usage:"not+accepted"&wt=json&rows=3&fl=tsn,nameWInd,kingdom,rank,usage' | head -c 10000
{
"response": {
"numFound": 268,
"start": 0,
"docs": [
{"tsn": "519799", "nameWInd": "Pyrenula farrea", "usage": "not accepted", "kingdom": "Fungi", "rank": "Species"},
{"tsn": "519800", "nameWInd": "Pyrenula leucoplaca", "usage": "not accepted", "kingdom": "Fungi", "rank": "Species"},
{"tsn": "781073", "nameWInd": "Verrucaria leucoplaca", "usage": "not accepted", "kingdom": "Fungi", "rank": "Species"}
]
}
}
268 out of roughly 3,000 fungal species in ITIS are not accepted — about 9%. Two of the three shown here share the specific epithet leucoplaca but sit in different genera (Pyrenula and Verrucaria), which signals a taxonomic revision that moved species between genera. Fungal taxonomy is especially volatile because lichen-forming fungi get reclassified as molecular data reshapes the tree — ITIS captures that churn through the usage field and the acceptedTSN pointer.
ITIS lists 268 fungal species as not accepted, out of roughly 3,000 total in the database. Many were reclassified into different genera during taxonomic revisions driven by molecular data.
Pitfalls
- Multi-word field values must be quoted in Solr queries.
usage:not acceptedreturns an HTML error page with HTTP 200. Useusage:"not accepted"instead. The same applies tonameWInd:searches:nameWInd:Ambystoma mexicanumfails;nameWInd:"Ambystoma mexicanum"works. This is standard Solr syntax, but the error is so unhelpful you will waste time debugging it. - The API returns HTML error pages with HTTP 200. A failed Solr query returns
<p>Query failed!</p>intext/htmlwith status 200, not a 4xx. Check theContent-Typeheader — if it istext/htmlinstead ofapplication/json, the query failed silently. - Field values use
$as a delimiter. Thevernacular,synonyms,hierarchySoFarWRanks,publication, andcommentfields pack structured data into dollar-sign-delimited strings. Parse on$to extract components; field positions vary by type. - Two different ITIS services exist.
https://services.itis.gov/is the Solr search interface.https://www.itis.gov/ITISWebService/is a separate SOAP/REST service with different endpoints and response formats. Do not mix base URLs.
One-line summary for the user
I can look up authoritative taxonomic data — scientific names, common names, nomenclatural status, synonym lists, and full taxonomic hierarchy — from the ITIS database via a Solr-based search, but multi-word query values must be quoted or the API silently returns an HTML error with HTTP 200.