Orchids are unique in the floral world. Two distinctive characteristics that set orchids apart from other plants are the labellum and the column.

The labellum is a modified petal.  It is extremely varied in appearance; “often lobed, spurred, adorned with glands, appendages of calli (callus, a hardened swelling or thickening of the skin), sometimes mobile and highly irritable and often brightly coloured”. * The labellum is important for pollination.

The column (as described by Bates and Weber) “is a distinctive feature of all orchids and a unique structure in the plant kingdom. It is formed by fusion of the male parts ‘stamens’ and female organ ‘pistil’.”*

Below are examples of the various types of labellums and columns in some South Australian terrestrial orchids. Each genus has its own characteristic labellum and column.

Thelymitra – though the labellum is almost indistinguishable from the other petals and sepals, the column is quite complex.

Dipodium or Hyacinth Orchid

Pterostylis or Greenhoods – generally a simple labellum with the column hidden well back into the hood.

Arachnorchis (syn Caladenia) can have quite varied and complex, mobile labellums

Corybas or Helmet Orchid – the labellum dominates and the column is hidden deep inside the flower.

Diuris or Donkey Orchid – the labellum is divided giving the appearance of more than one structure.

*Bates and Weber Orchids of South Australia 1990