Since the opening of the new Tropical Wetlands display in May, star plant the Santa Cruz waterlily (Victoria cruziana) has been producing a succession of enormous, ferociously spined lilypads up to 1.5 metres in diameter and each with a huge upturned notched rim of up to 20 centimetres. To make room in the 12,000 gallon pool, staff have been cutting off and turning over the largest to show the elaborate vaulted ribbing that supports the leaf. Now, this plant of the Paraguyan waterways is beginning to flower, sending up large waxy waterlily flowers one after the other, again heavily spined at the base. The flowers last but 48 hours, but the biology is fascinating – a tale of sex change and entrapment.
The flowers open in the evening, the many white petals unfolding to provide a large and high-vis landing platform for scarab beetles (Cyclocephala hardyi), inexpert fliers, which pollinate the plant in the wild. As the flower opens, its temperature increases by up to 20 degrees above the ambient which encourages the diffusion of an enticing pineapple scent, luring the unsuspecting scarab beetles with the promise of a nutritious, starchy feast held within the large floral chamber.
All night the scarab beetles feast and as they do so scatter pollen from the flower they visited the night before. As dawn breaks, the flower closes up preventing the scarab beetles scarpering to freedom. When the flower opens again that evening, the petals have become flushed pink and purple and the scent is lost, indicating that the flower no longer has receptive female parts but is now in an active male phase. As the beetles exit the floral chamber, they are loaded with shed pollen which they then carry to the next white, pineapple-scented flower in female phase, and cross-pollination is effected. Fertilized flowers then sink back below the water.
Staff expect the Santa Cruz lily to flower continuously from now until the autumn, but are considering removing some of the flowers to ensure that the plant’s energy is also diverted into producing the enormous lilypads.
The Victoria waterlily is said to have inspired Joseph Paxton in his design for the Crystal Palace, and also influenced the design of the Fountain by cutler, David Mellor, that heads the Main Walk at the Garden.
Growing with the Victoria waterlily is the sacred lotus, Nelumbo, also on the point of flowering. The beautiful glaucous and rounded leaves of this plant are well known for the ease with which they repel water – droplets collect and roll from the leaf. This lotus effect has inspired engineers to develop self-cleaning surfaces based on the leaf surface structure of the Nelumbo.