It has a single thin, hollow, onion-like leaf and up to ten small green flowers.

It differs from the other two onion orchids in New Zealand, (M. unifolia and M. parviflora) in being a much smaller plant with a more pointed dorsal sepal.

Microtis oligantha is a terrestrial, perennial, deciduous, herb with an underground tuber and a single erect, smooth, tubular leaf up to 200 mm (8 in) long.

[2] Microtis oligantha was first formally described in 1968 by Lucy Moore from a specimen collected on the edge of Lake Roundabout east of Ashburton and the description was published in the New Zealand Journal of Botany.

[4]: 338 The small onion orchid grows in damp grassland and meadows in montane and subalpine parts of both the North, South and Chatham Islands.