Orchid flowers (Dendrobium helix). This orchid is known as the corkscrew orchid because of the elongated and twisted shape of two of its three petals. The third petal (centre left on the flower in the foreground) is the specialised lip, a petal on which pollinators land. The other petal-like structures are actually sepals. This orchid grows on trees (it is said to be an epiphyte) in the lowland tropical forests of New Guinea. There are more than 30,000 species of orchids worldwide, many of which are grown as ornamental flowers.