Complex sentence: The "flowers" of "Protea cynaroides" are actually composite flower heads (termed an "inflorescence") with a collection of flowers in the centre, surrounded by large colourful brac, from about 120 mm to 300 mm in diameter.
Split into simpler sentences: The "flowers" of "Protea cynaroides" are actually composite flower heads (termed an "inflorescence") with a collection of flowers in the centre, surrounded by large colourful bracts. The flowerheads vary in size, from about 120 mm to 300 mm in diameter.