The fact that the flower colour of Gladiolus liliaceus changes between day and night was first noted by the botanist Henry Andrews as long ago as 1798. Veld and Flora (June 2011) published an interesting article on a school project in Japan. A high school teacher in Japan decided to investigate this strange phenomenon by looking at the cellular structure of the tepals of Gladiolus liliaceus, an indigenous South African bulbous plant much admired by the international flower trade as it is easy to cultivate. The article ‘The amazing colour-changing flower’ is the actual study undertaken by a high school class in Japan. It is an excellent study on how to set about a scientific investigation and “hypothesis testing” study for Grade 12. Using the step by step instructions the article shows how the high school students in Japan worked out what was making the flower change colour.
Gladiolus liliaceus has the incredible ability to change colour after nightfall; the drab light brown flowers become bluish to mauve and intensely sweetly clove-scented. The flowers has a particularly interesting flowering physiology. The tepals of the large flowers are partly closed during the day and coloured a translucent rusty red, cream or brown. At sunset the tepals undergo a rapid change to a light, translucent mauve. At the same time the tepal open more widely and the flowers release a strong, heady scent redolent of carnations and cloves. The behaviour is clearly an adaptation to pollination by moths, two species of which have been recorded visiting the flowers. Large long-tongued moths are rewarded by large quantities of sweet nectar which is held in the lower half of the perianth tube.
Gladiolus liliaceus, commonly known as the Large Brown Afrikaner, Aandblom or Ribbokblom, occurs on clay slopes mainly in renosterveld in the south-western and southern Cape – roughly from the Cape Peninsula to Leliefontein and Ceres to Port Elizabeth. Here in the Knysna area I have found a few specimens growing on the hilly pastures of the Eastern Head.