Transitivity Failures in Taxonomic Name Resolution: Implications for Botanical Dataset Construction

What this was about

Adam Richard-Bollans shows that resolving names to accepted names across taxonomy versions is not transitive: a name x resolved to y in one version may not resolve to where y resolves in a later version, e.g. because heterotypic synonyms are split. Comparing World Checklist of Vascular Plants versions (2022 vs 2025), about 13,000 of ~1.4 million names (≈1%) disagree, about half at species level, implying ~0.5% species-level error in datasets that kept only accepted names, rising to 0.7% by June 2026. Errors cluster in western and southern Europe (France, Italy, Spain).

Why it matters. Many secondary datasets discard original names after resolution; this quantifies the silent error that introduces and shows it grows over time.

In the room

• Most aggregated botanical datasets resolve names to accepted names and often discard verbatim names.
• Transitivity: x→y in v1 and y→z in v2 should imply x→z in v2; heterotypic synonym splits break this.
• Example: Panicum nitidum resolved to Dichanthelium dichotomum in WCVP v10 (2022), but to Dichanthelium nitidum in v14 (2025).
• ~13,000 of ~1.4 million names disagree (≈1%); about half at species level, some at genus level.
• Regional clustering of non-transitive resolutions in western/southern Europe.
• Error grows with time since the original version (0.5% in 2025 to 0.7% by June 2026 for a 2022 dataset).
• World Flora Online results are more severe; resolving to a different taxonomy likely increases error further.

Notable moments