The effect of indigenous languages of South America on Spanish is strongest in the lexicon (especially with toponyms, zoonyms, and phytonyms) and identifiable, but much more modest, in phonetics/phonology (e.g., vowel variability and reduction and nasalization) and morphosyntax (e.g., the different use of selected verb forms and constituent order). The phenomena called Media Lengua and Yopará differ from this picture in that the former roughly consists of a Spanish lexicon combined with Quechua grammar, while the latter is a fluid Guaraní-based system with numerous borrowings from Spanish. The effects of contact are socially and areally variable, with low-prestige, typically rural, varieties of South American Spanish showing the most significant systemic impact, while high-prestige, typically urban, varieties (including the national standards) show little more than lexical borrowings in the semantic fields mentioned. This result is hardly surprising, due to historical/sociolinguistic factors (which often led to situations of dominance and language shift) and to the typological dissimilarities between Spanish and the indigenous languages (which typically hinders borrowing, especially of morphological elements).