Wednesday, October 13, 2010

Flowering bamboo

Unlike most grasses, bamboos rarely flower. Flowering, when it does occur, can range from a few spikelets of flowers on isolated culms to complete flowering of an entire population no matter where it is located on the planet (an event called “gregarious” or “mass flowering”).

There is a lot of mystery surrounding the flowering of bamboo, and the exact mechanisms triggering it are poorly understood. Gregarious flowering of bamboos is one of the big enigmas of the natural world: How do plants originating from the same genetic source know that the time has come to go into flower? Some bamboo species are on a relatively predictable flowering cycle (say, every 30-50 years), other species have never been known to flower.

Running bamboos often recover even from a complete flowering while most clumping bamboos die. Western gardeners may bemoan the loss of a beloved plant, but in countries where bamboo is an important source of food or construction material, mass flowering can have dire consequences.

Case in point: the Indian state of Mizoram where large tracts of land are covered by forests of Melocanna baccifera, a species that goes into flower every 44-48 years. It produces huge amounts of avocado-sized fruits full of protein-rich seeds. (This, in itself is fairly unique since only a very few bamboo species produce fruits while the vast majority just produce cereal-like seeds.) The abundance of Melocanna fruits and seeds typically leads to a rapid multiplication of the rat population which then proceeds to devour vital crops such as rice and potatoes. In 1958-59, this resulted in a famine which caused the death of 10,000 to 15,000 people. The Mizo people of Mizoram state call the flowering of Melocanna baccifera “Mautam”, and it has had significant economic and political consequences. For an in-depth description of the Mautam phenomenon, see this article and this one.

Another mass flowering occurred in the Indian state of Manipur just this year, and other Asian countries such as Myanmar and Thailand are routinely affected as well.

In the U.S., bamboo is not of much economic significance so when a bamboo species begins to flower, it’s of interest only to bamboo growers and people who have that species planted in their yard.

I currently have two species flowering: Pleioblastus shibuyanus ‘Tsuboi’, a small running bamboo with nicely variegated leaves, and Bambusa textilis ‘Mutabilis’, a large clumping bamboo that has the potential to grow to 35 ft.

I bought my Pleioblastus shibuyanus ‘Tsuboi’ as a small plant last fall and it began to decline almost right away. Within weeks, new culms came up but they had no leaves, just flowers. Pretty quickly, almost all leaves on the existing culms fell off and the plant looked like it was going to die. Now, 9 months later, the plant is hanging on, but barely. One culm still has a few leaves, and from the seed that was produced two seedlings have come up. Unfortunately, they are green, with no sign of the variegation that made ‘Tsuboi’ so special. ‘Tsuboi’ appears to be in the midst of a gregarious flowering cycle, and I’m hoping that somebody will be lucky enough to find a variegated seedling growing in their yard.

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Flower on Pleioblastus shibuyanus ‘Tsuboi’, February 2010

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Results of flowering on ‘Tsuboi’, October 2010

My other flowering bamboo, Bambusa textilis ‘Mutabilis’, is a very recent addition to my collection. I bought it about a month ago at Bamboo Sourcery’s going-out-of-business sale. I didn’t notice the flowers until after I got back, but it appears that only the branches on one culm have flowers while the rest of the plant is unaffected and growing happily. In fact, there are two new culms (canes) that have been growing rapidly, and many new leaves are being produced as well. It certainly looks like this is a case of partial flowering, possibly induced by the stress of being stuck in a pot that’s too small for the plant. I’m keeping a close eye on the plant but I expect it to live and thrive.

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Flower on Bambusa textilis ‘Mutabilis’, October 2010

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New culm on Bambusa textilis ‘Mutabilis’, October 2010

P.S. As you can see in the photos above, bamboo flowers are nothing to write home about. Since the pollen is distributed by the wind, there’s no reason for showy flowers that would attract animal pollinators.

More information about the flowering of bamboo can be found on the web site of the American Bamboo Society.

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