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The cool blue seeds of the Malagasy traveller’s tree

Wolfgang Stuppy
6 March 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)

Attracting animals

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.

The answer lies in the very special fauna of the island. 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 -
 


 

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Comments

27 October 2013
Comment: 
We have one right outside our 2nd floor apartment window in Miami Beach, Florida USA. The seed pods have sprung open to reveal the most amazing color blue seeds.
3 August 2012
Comment: 
Especially, since Madagascar is being deforested so rapidly. I was asked one time, if the five species of bamboo lemurs were to became extinct, how would like affect the 19 species of mouse lemurs. My answer was that bamboo would start growing and crowding out the angiosperms. Angiosperms provide the fruit, flowers, and gum that the mouse lemurs feed upon. So we are seeing what mouse lemurs and ring-tailed lemurs feed upon, if it was threatened.
15 March 2012
Comment: 
Hello Wolfgang, Great to come across this blog post... especially given you've featured these extraordinary blue seeds with the captivating story. I imagine this was a thrilling discovery ... were you sent these at the MSB or did you actually find them in-situ on a trip? On first sighting last October when with you all over there these seeds looked like small colourfully-wrapped gifts. My photos of them are so imprecise but still capture the colour. I will have to link this to my blog. Greetings to you all over there! Sophie M, from Brisbane
8 March 2012
Comment: 
This is fascinating! I immediately thought of blueberries, though, and wondered whether fruits were more likely to be blue than seeds, and what this might say about their dispersal. Great post!
6 March 2012
Comment: 
Interesting comment from Daniele. I have not yet found this relationship or any other of that kind published anywhere. I pieced this together myself from the available facts as described in the text above. However, a few months ago , I have discussed my 'hunch' with Sir David Attenborough when he visited the MSB for some filming and he confirmed to have seen lemurs in Madagascar feeding on the seeds (or rather their arils) of Ravenala. It would be interesting to investigate the significance of the difference in morphology and texture between the arils of Ravenala and Strelitzia/Phenakospermum. The texture of the aril of Ravenala is similar to wax paper whereas the arils of the latter two is more like a tuft of thick, dry hairs. I can only guess, but this might reflect the different feeding preferences of these two animals groups or some practicalities to do with harvesting and/or aril removal.
6 March 2012
Comment: 
It is a very interesting story. I wonder if other examples of "blue seeds/prosimians" interactions have been described. There is also a striking difference in the shape of the appendices between Ravela and Strelitzia seeds. Does it contribute to seed dispersal?

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