Tuesday, November 10, 2015

An ultra-rare and DNA-rich relative of the coconut

A dozen or so solitary trees scattered within a remote part of northeastern Madagascar are all that remains of Voanioala gerardii in its natural setting.

In Malagasy, the national language of the large African island, the plant is called voanio-ala. This translates to 'forest coconut', which is appropriate given that the coconut (Cocos nucifera) is one of its closer relatives. Incidentally, the genus names assigned to several other palm trees found on Madagascar (e.g. Marojejya and Raphia) were also derived from the Malagasy language.

The species is named for Gerard Jean, who collected the tree fragments that sparked the interest of John Dransfield, a palm researcher at Kew. Dransfield came over from the UK to investigate the tree and subsequently named and described it in a scientific publication.

Like the coconut, V. gerardii grows as a tall tree (15-20 m high, compared to the 30 m maximum height attained by coconut trees) with a bare trunk and a bunch of long leaves (~5 m in length) at the very top. Both trees are harvested for their palm hearts (the scrumptious inner core of the stems of young trees) and large edible fruit (which grow in clusters).

While coconuts naturally occur on beaches (spreading via the ocean due to their buoyant fruit), V. gerardii tends to grow inland (thus being called the forest coconut).

It's been suggested that its seeds, which currently pile up under mature trees, were once dispersed by now extinct birds or mammals who were large enough to carry them around. This helps to explain why the tree hasn't spread elsewhere and is going extinct (habitat loss and being eaten by humans aren't helping much either).

DNA-filled nuclei of (a) Voanioala gerardii and (b) an onion (Source)

Among monocots, V. gerardii has the highest known number of chromosomes, with each of its cells containing close to 600 of the DNA threads. This large number is due to many instances over the evolutionary history of the plant where its existing set of chromosomes (i.e. its genome) underwent duplication. Cells of the plant also contain a relatively large amount of DNA, as shown in the above image.


References

Dransfield J. 1989. Voanioala (Arecoideae: Cocoeae: Butiinae), a new palm genus from Madagascar. Kew Bulletin 44(2):191-198. [First page]

Dransfield J. 1992. Voanioala, the forest coconut. Principes 36(3):124-127. [Full text]

Johnson MAT, Kenton AY, Bennett MD, Brandham PE. 1989. Voanioala gerardii has the highest known chromosome number in the monocotyledons. Genome 32(2):328-333. [Full text]

http://www.arkive.org/forest-coconut/voanioala-gerardii/

http://www.palmpedia.net/wiki/Voanioala_gerardii

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