Extra-stemmatic – or according to Trovato (2014, 134) preferably called 'extra-archetypal' – contamination is contamination by a lost witness that stems from a branch of the tradition which branched off before the tradition's archetype. Such contamination may thus preserve some readings that go beyond the archetype. Trovato (2014, 289–297, cf. illustration below) believes this to be the case e.g. in the stemma of the Lai de l'Ombre (see Bédier).
The term was coined by Timpanaro (appendix c) who contrasts it to intra-stemmatic (that is "normal") contamination.
Trovato (2014, 294): Extra-stemmatic contamination happened from lost witness r to z.
– – Timpanaro, Sebastiano. 1981. La genesi del metodo del Lachmann. 2nd ed. Padova: Liviana. – 1st ed., Firenze: Le Monnier, 1963.
– ———. 2005. The Genesis of Lachmann’s Method. Translated by Glenn W. Most. Chicago: University of Chicago Press. – Translated from Timpanaro 1981.
– Trovato, Paolo, 2014. Everything you always wanted to know about Lachmann’s method: a non-standard handbook of genealogical textual criticism in the age of post-structuralism, cladistics, and copy-text; foreword by Michael D. Reeve. Firenze: Libreriauniversitaria.it edizioni.
In other languages
DE: extrastemmatische Kontamination
FR: contamination extrastemmatique
IT: contaminazione extrastemmatica