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The largest flowers in the world belong to Rafflesia genus, found in southeastern Asia (Malaya, Borneo, Sumatra, Philippines).
The biggest of all is that of R. arnoldii, from Borneo and Sumatra: 11 kg, 1 m (3 feet) wide. The flower is blood-red and spreads a rotten-flesh stink, which attracts carrion flies for pollination.
But since the discovery of these plants - less than two centuries ago - they posed an enigma. Rafflesia are parasitic plants with an unusual trait. As they live on the jungle floor, extracting food from the roots of a tropical vine (Tetrastigma), they lost all organs: stem, roots, leaves. As they do not make photosynthesis,
Rafflesia do not need those organs. So, scientists found it very difficult to classify these species, creating a whole family only for them, Rafflesiaceae, and an order, Rafflesiales. "These plants are so strange - almost extra-terrestrial - wherever they were placed [within the family tree] there would be a lot of explaining to do", said Charles Davis, assistant professor of organismic and evolutionary biology at Harvard University.
But in the DNA analysis era, this obstacle could be surpassed, and to their surprise, the bizarre plants were proven to belong to the Euphorbiaceae family. The big surprise was that all plants in these family bear tiny blooms.
The most economically important species in this family are the rubber tree, castor oil plant and the cassava shrub, but in the temperate zone the most known spontaneous species are the spurges. "The big shocker, of course, is that they fall in the middle of this group with minute flowers", added Davis.
DNA analysis showed that 46 million years ago, the plants' blooms began to evolve at an accelerated pace, increasing from a tiny 2mm (0.08in) up to their enormous size. "These plants occur exclusively in tropical rainforest under-storeys, which are very dimly lit, and they are restricted to the forest floor. They don't have an easy way of presenting their flowers to various insects for pollination", said Davis. "By maximising their surface area it is much easier to waft the funky smell further