Complex sentence: Cultivated varieties have been grown since at least the 16th century, with a great increase in varieties during the 1800s; in particular, the first really widespread cultivar, the Kentish Cobnut, was introduced in 1830.
Split into simpler sentences: Cultivated varieties have been grown since at least the 16th century, with a great increase in varieties during the 1800s. In particular, the first really widespread cultivar, the Kentish Cobnut, was introduced in 1830.