Complex sentence: The acorns are 2-3 cm long and 1.5-2 cm diameter when mature about 18 months after pollination, held in a cup covered in dense, elongated, reflexed scales.
Split into simpler sentences: The acorns are 2-3 cm long and 1.5-2 cm diameter when mature about 18 months after pollination. They are held in a cup covered in dense, elongated, reflexed scales.