Although most English speakers don't distinguish between the two kinds, the fruit of the chestnut tree varies: marroni are generally sweeter, with finer flesh than their near-chestnut relation, castagne. They are the ones that go into marrons glacés, which both the Italians and French claim to have invented.
There are a number of protected IGP and DOP varieties grown throughout Italy:
Marrone di Caprese Michelangelo DOP (Emilia-Romagna)
Marrone di Castel del Rio IGP (Emilia-Romagna)
Marrone di Combai IGP (Veneto)
Marrone del Monfenera IGP (Veneto)
Marrone del Mugello IGP (Tuscany)
Marrone di Roccadaspide IGP (Campania)
Marrone di San Zeno DOP (Veneto)
Marrone della Val di Susa IGP (Piedmonte)
In October, Cuneo in Piemonte holds the Fiera Nazionale del Marrone.
Image by Robert Young