The cool blue seeds of the Malagasy traveller’s tree
By: Wolfgang Stuppy - 06/03/2012
Truly blue seeds are about as rare as hens’ teeth. In the first of his ‘Seed of the Month’ series, Millennium Seed Bank seed morphologist, Wolfgang Stuppy, explains why.
Seed of the Month - Ravenala madagascariensis
The most amazing blue seeds I have ever come across belong to the Malagasy traveller’s tree (Ravenala madagascariensis).
Malagasy traveller’s tree (left) and a single seed (right)
If blue is such a rare colour among seeds, there must be a good reason why the Malagasy traveller’s tree seeds have evolved such an exotic colour. The reason behind it is a fascinating example of the tightly interwoven natural history of plants and animals.
The Malagasy traveller’s tree is a close relative of the bird-of-paradise (Strelitzia reginae) from South Africa and the very similar big palulu (Phenakospermum guianense) from South America.
Fruits of Malagasy traveller’s tree (left) and big palulu (right) (Images: Wolfgang Stuppy © RBG Kew)
All three species belong to the Strelitziaceae family and all three produce seeds with edible appendages to attract animals for their dispersal. However, whilst the edible appendage of the seeds of Strelitzia and Phenakospermum has the appearance of a bright orange-red ‘wig’, the seeds of Ravenala are wrapped in an intensely blue, soft, wax-paper like appendage.
The red and black colour scheme is typical of, and very common in, bird-dispersed fruits and seeds whereas blue is extremely rare indeed.
Bird-of-paradise flower (left) and its seeds (right) (Images: Wolfgang Stuppy © RBG Kew)
So why are they blue?
Clearly, there must be a reason why Ravenala, geographically isolated in Madagascar, has evolved seeds with an intensely blue rather than red appendage. To the best of my knowledge, nobody has answered this question yet, but based on various pieces of evidence, I believe that the answer lies in the very special fauna of the island. So here goes my theory: There are not many fruit and seed eating birds in Madagascar so some plants have entered co-adaptive relationships with other animals to achieve the dispersal of their seeds. One such alternative are the lemurs, a diverse group of primates endemic to Madagascar.
Seeds of Ravenala madagascariensis (left) and a ring-tailed lemur from Madagascar (right)
And here comes the interesting fact...
Prosimians (‘half-apes’) such as lemurs and lorises (a related group of ‘half-apes’ found in Asia), have dichromatic vision and can only differentiate shades of blue and green but not red - whereas birds have very similar colour-vision to humans. So the shaggy red ‘wigs’ of the seeds of the bird-of-paradise flower would be wasted on the lemurs of Madagascar.
- Wolfgang -
- The Millennium Seed Bank partners in Madagascar
- Kew's Madagascar science team
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