Today’s entry was written by Tamara, who scribes:
For this BPotD entry, I chose to compare two species of Clivia in order to highlight how one species in a group has evolved to use a different set of pollinators. Thank you to the late James Gaither (aka J.G. in S.F.@Flickr) for his photo of Clivia caulescens taken at the San Francisco Botanical Garden, and to Priscilla Burcher (Priscilla Burcher@Flickr) for her image of Clivia miniata taken at the Walter Sisulu National Botanical Garden in South Africa.
Clivias are endemic to South Africa and Swaziland. These yellow, orange, or red-flowering plants have been popular ornamental species in Western gardens since they were first collected by the British explorers William Burchell and John Bowie in the early 19th century. Clivias have long, dark-green strap-shaped leaves and are adapted to the low-light conditions of the forest floor. They have been extensively bred for ornamental qualities, and even have a global fan base (check out the Global Clivia Enthusiast Forum if you also share this passion). Clivia miniata is the most-cultivated of the genus, commonly called Natal lily or bush lily. It reaches a height of about 45 cm, and in its native habitat grows in well-drained, humus-rich soil of forest floors or, rarely, in the fork of a tree. Clivia caulescens is rarely cultivated. This species has an unusual stem for a Clivia, which reaches to 90cm in height with aerial roots along its length.
Natal lily is the only Clivia that is pollinated by butterflies, while Clivia caulescens, like all other species of Clivia, is pollinated by sunbirds. The botanists Ian Kiepiel and Steven D. Johnson, in the 2013 article Shift from Bird to Butterfly Pollination in Clivia assert that the ancestor of Natal lily was a sunbird-pollinated species like the other members of the genus. In the evolution of Clivia miniata, a transition to butterfly pollination occurred. One of the most pronounced shifts found by Kiepel and Johnson was that the flowers went from the pendulous, tubular flowers exemplified by today’s image of Clivia caulescens to the upright, trumpet-shaped flowers of Clivia miniata. This change is best explained by examining the pollinating methods of sunbirds compared to butterflies. Sunbirds desire a perch while consuming their nectar, and the drooping flowers of Clivia caulescens allow these birds to perch on the flower stem and probe upwards for the nectar. Upright flowers, on the other hand, are nearly impossible for these birds to reach when perched on the stem. Rather than a perch, butterflies need a landing pad, which the upward-facing flowers of Clivia miniata provide. Upwards-facing flowers also allow the species to take advantage of butterflies that brush past as they explore and claim territory, collecting pollen on their wings and dispersing it onto the upright stamens. Kiepel and Johnson point out that these flower forms are similar to those found in other genera pollinated by either sunbirds or butterflies, respectively.
Other differences in flower physiology include lower pollen production and greater scent in Natal lily than in other members of the genus; birds require a greater amount of pollen than butterflies do, and rely much less on their sense of smell. The characteristics that did not change when the species shifted its pollination strategy are as interesting as those that did. Flower colour – a vibrant orange-red possessing a high UV reflectance, is the same for the sunbird and butterfly-pollinated clivias. Sunbirds and butterflies both have UV receptors, and are likely to be able to perceive the clivias in a very similar fashion. It is likely that this similarity in visual perception is one of the factors that made the change in pollinators possible. In case you want to know what a Clivia miniata flower looks like to a sunbird or butterfly, see Dr. Klaus Schmitt’s image on the Photography of the Invisible World site.