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Rotenone flowers

March 3, 2013

Tuba root or rotenone (Derris elliptica syn. Paraderris elliptica, Fabaceae) is a liana of the bean family currently in blossom at Dokmai Garden in Chiang Mai. Some people in Malaysia and Thailand used to crush the root in a barrel of water and then empty the water into a stream or pond to stupefy or kill fish. The insecticidal rotenone chemical prevents oxygen uptake in gills. ’Tuba’ is a Malayan word for the plant.’Roten’ is the Japanese name. ’Hang lai daeng’ or ’lai nam’ are northern Thai names.

The industrial rotenone chemical has been used to wipe out predatory fish in lakes to make way for breeding trout and other economical fish. Sometimes rotenone has been used to eradicate invasive exotic fish species (and all other fish too) in water restoration projects.

Many tropical gardening books suggest one should crush the seeds and extract the rotenone chemical as a home-made pesticide. That seemed to be a good piece of advice, but the many recent studies linking neurotoxic pesticides, natural or artificial, with Parkinson’s disease show that rotenone may be dangerous to your health. To a Stone Age fisherman with an average life span of 30 years rotenone-poisoned fish would not be a primary problem, but for modern man who lives longer a repeated damage to the nervous system should be avoided. Chewing the raw root is a suicidal technique in New Guinea according to Mabberley‘s Plant-book.

The Greek word ’derris’ means ’membrane’, ’skin’ or ’leather’, and refers to the leathery seed pods. The genus name was coined by the Portuguese Jesuit Joao de Loureiro in 1790 (Flora Cochinchinensis vol.2 page 432). The newer genus name ’paraderris’ means ’beyond derris’. That name was coined by Friedrich Anton Wilhelm Miquel in 1855 as a section of the genus Derris, but erected to genus by Robert Geesink in 1984.

The differences between the two genera Paraderris and Derris do not seem very clear but generally Paraderris has 2-3 (5) flowers at each branchlet tip, while Derris has more flowers scattered along the branchlet. However, pedigrees based on recent (November 2012) DNA analyses by Yote Sarichamorn and colleagues show that Paraderris is not different from Derris and so should no longer be used.

Smitinand (2001) lists 12 species of Derris (including Paraderris) in Thailand.

The rotenone plant was originally described in 1832 by Nathaniel Wallich as Pongamia elliptica, later transferred to the genus Derris by George Bentham, and even more recently (2000) transferred to Paraderris by Fredericus Adema. As mentioned above research published 3 months ago show that Paraderris should no longer be used. Keeping track of the scientific names and their synonyms is difficult. The famous Plant List treats the two names (Derris elliptica and Paraderris elliptica) as two accepted species while in fact they refer to the same plant, and the famous Flora of China and Mabberley’s Plant-book (2008) treat rotenone as Paraderris elliptica which is now obsolete.

For a tropical garden enthusiast or nature lover the sheer number of tropical plant species is enough to suffocate the urge to learn more about them. In addition, as shown in this blog the botanical nomenclature may seem hopelessly complicated, and there is not one source of information but publications are scattered and often unavailable outside the universities. These three facts, and a widespread inability to digest international publications due to language problems, create a threshold explaining the general lack of knowledge about plants growing in Southeast Asia. A general lack of knowledge is dangerous since destruction may go on without notice until too late. We hope Dokmai Garden and Dokmai Dogma will help bringing some enthusiasts above that threshold, and we are grateful for corrections and additional information.

Replacing the fantastic Southeast Asian forests with rubber trees, teak plantations, corn fields and Mexican sunflowers would make the world a poor and ugly place. It would be like replacing a thousand different restaurants and their delicious menus with a brightly coloured, factory-made and sweetened goo. Children who never tasted anything else would call it food.

Derris elliptica.March3.2013.72At Dokmai Garden we grow rotenone in a shady and regularly moistened area. It will shed its leaves during the cool dry season but immediately respond to the warmer nights in mid February and start making Wisteria-like leaves and flowering buds resembling golden acorns. These buds will soon burst into very attractive flowers, reminding me of Cleisostoma simondii orchids, bleeding heart (Dicentra spectabilis) or chocolate, strawberry, pistachio and vanilla ice cream.

Text & Photo: Eric Danell

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