In practice, the names hazelnut and filbert are interchangeably used for any of the 15 species and numerous varieties in the genus Corylus. In cooking and nut marketing, the term hazelnut is often used because it sounds sexier. It’s all very sketchy, but the name filbert may have come from the fact that in Britian, the nuts begin ripening around St. Philbert’s day, in late August. Or it could have come from the un-hip sounding voll bart, from the German for ‘full beard’ in reference to the appearance of the husk around the shell. Full beards? Beards, certainly, but not ‘full beards’. In general though, if you want to be more specific, ‘filberts’ are the European natives C. avellana and C. maxima. The nuts are medium sized and elongated. The large subspecies C. avellana grandis is referred to as ‘cobnut’, while the cultivar C. avellana ‘Barcelona’ is a very large, round nut sometimes called the Oregon hazelnut. ‘Hazelnuts’ then, are the American natives C. americana, C. cornuta and C. corlurna. Several species of Corylus native to Asia also are called hazelnuts.

If you want to get really technical, here are the accepted scientific and common names of the most widely grown species, according to the USDA Plants Database:

C. americana American hazelnut
C. avellana Common filbert
C. corlurna Turkish hazelnut
C. cornuta Beaked hazelnut
C. ferox Himalayan hazelnut
C. heterophylla Siberian hazelnut
C. maxima Giant filbert

More hazelnut/filbert terminology, for use in ice cream shops abroad:
Italian Nocciola
French Noisette, hazelnut, Aveline, filbert
German Haselnuss
Spanish Avellana

I remember hearing from a friend that Filberts and Hazelnuts are actually slightly different, but I’m curious to know whether that’s actually the case, or whether it’s REALLY just a local name thing.

Anyway, thanks for the lovely sights and info!

-Amber