Sunflowers. Two sunflowers (Helianthus sp.) in bloom. Sunflowers are grown commercially for the oil obtained from the seeds. The plants can grow up to 3 metres tall, whilst the large solitay bloom can be up to one metre in diameter. The oil is used widely in cooking and as a base for soaps and candles. The flower is a compound of many smaller flowers, which form the dark inner portion, as well as the yellow petals.