Mucuna gigantea  (Willd.) DC. 1825

pronounced: myoo-KOO-nuh gy-GAN-tee-uh 

(Fabaceae – the pea family)

subfamily: Faboideae – the bean subfamily

common names:  Burny Bean, Velvet Bean

Mucuna mucuna giganteaburny beanmucuna gigantea leafleafis from the Brazilian name for these vines; gigantea is from the Latin giganteus, of or belonging to the giants. Mucuna is a genus of about 100 species of climbing vines and shrubs, found worldwide in tropical woodlands. The pods of some species are covered in coarse hairs that contain the enzyme mucunain, and cause itchy blisters when they come in contact with the skin. Specific names such as puriens (Latin for ‘itching’) and urens (Latinized Greek for ‘stinging like a nettle’) are testimonies to this. Mucuna pod hairs were a common ingredient in the itching powder once loved by practical jokers. On the other hand, the hairless parts of some species are used by some South American shamans to make an entheogenic snuff.

Burny Vine is a tall climber, usually high in trees; the young stems are hirsute, becoming glabrous as they age. The leaves are trifoliate, the leaflets ovate to lanceolate, 7.5–16 cm long, 2–9 cm wide, the margins entire, glabrous.

mucuna gigantea budsbudsmucuna gigantea flowersflowersThe inflorescence is an umbel on a peduncle to 12 cm long, with the flowers pea-shaped to 7 cm long, the petals a pale green.

The flattened black pod is up to 15 cm long and 5 cm wide, winged, with irritant hairs present. There are 2–6 (usually 3) seeds per pod, about 2 cm in diameter.

The vine grows in coastal forests of northern NSW, Queensland and the Northern Territory. Sir Joseph Banks collected it near present-day Cooktown while the Endeavour was being repaired there in 1770. On Magnetic Island, I have seen it growing on the banks of Gustav Creek and by the track leading off from the far end of Mandalay Avenue in Nelly Bay, and in the scrub around the lagoon in Horseshoe Bay.

The flowers are fertilized by nocturnal bats. The clusters of blossoms hang down from the forest canopy where the bats can easily access them. The bats brush against the flowers as they sip the sweet nectar, and shift pollen from one plant to another.

mucuna gigantea with green antsgreen ants on burny beanAfter pollination and the development of the seed pods, the seeds fall from the plant. The seeds have a hard, woody seed coat that makes them impervious to water, and also contain internal air cavities that enable them to float. They are washed down gullies and creeks and thence into rivers that eventually flow into either the Atlantic or the Pacific Ocean. They drift for months (or even years) in the sea, eventually washing ashore on a distant coast. They are often collected by natives and polished to be used in making necklaces and bracelets.

You will notice in the photographs that the base of the inflorescence, in particular, is much loved by our green ants. They are probably harvesting tiny scale insects from the surface of the plant.

The seeds themselves appear to be immune to seed predators, which, besides being deterred from the stinging hairs on the seed pods, probably dislike the bitter, potentially toxic amino acid, L-dopa, that the seeds contain.

Butterfly larvae that feed on the leaves include the Common Aeroplane Phaedyma shepherdi and the Green Awl Hasora discolor.

 Photographs taken at Horseshoe Bay 2011

Page last updated 28th January 2018

 

 

 

 

 

 

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