Brush-like fireball lily is specialized for butterfly visits
On butterfly wings, the pollen of fireball lily, Scadoxus multiflorus, is transferred from one plant to another, as Hannah Butler and Steve Johnson show.
Like bees, butterflies are pollinators. They visit flowers to drink nectar, pick up pollen and deposit pollen grains on the pistil when visiting the next flower. Flowers pollinated by butterflies are often red or orange, because that colours are attractive to butterflies. In addition, the structure of the flowers is specialized for butterfly pollination, write Hannah Butler and Steve Johnson.
The ‘salver form’, in which petals form a platform on which a butterfly can settle while inserting its proboscis into a flower, was already known. In this model, pollen grains stick to the proboscis and the head of the butterfly. Now, Butler and Johnson describe another flower form with a different pollen transfer mechanism: the ‘brush model’.
A brush model plant is fireball lily, Scadoxus multiflorus, of Africa, also known as indoor plant. The stamens and pistils extend beyond the petals, and because the flowers are placed close together in an umbel, stamens and pistils of different flowers overlap. The plant cannot fertilize itself; pollen has to be brought from another plant for seeds to develop.
Large butterflies that visit the plant do the job. A frequent visitor is the mocker swallowtail Papilio dardanus, principally males. How does it transfer pollen from one plant to another?
The butterfly flutters along the inflorescence to inspect it, touching many stamens and pistils with the wings. When drinking nectar, it continues fluttering. The flat pollen grains from the stamens it touches stick between the scales at the ventral surface of the wings, as macro photos show. And part of the grains that a butterfly carries with it will fall on the pistils; the butterfly can pollinate several flowers during a single visit, even when it doesn’t drink nectar.
So, the brush-shaped umbel is a specialisation for butterfly-wing pollination. The fireball lily belongs to the amaryllis family. As it turns out, other red flowers of that plant family also have a brush model and deposit their pollen on butterfly wings.
Willy van Strien
Photo: Mocker swallowtail Papilio dardanus (male) on fireball lily Scadoxus multiflorus. ©Steven D. Johnson
Butler, H.C. & S.D. Johnson, 2020. Butterfly-wing pollination in Scadoxus and other South African Amaryllidaceae. Botanical Journal of the Linnean Society, online March 12. Doi: 10.1093/botlinnean/boaa016