The Noble Rhubarb: Himalayan Marvel of Nature’s Ingenuity

At almost two meters tall, the Noble Rhubarb (also known as Sikkim Rhubarb) stands out – just a little - in its Himalayan habitat. While nature has designed its neighboring herbs and shrubs to grow short and stumpy, this species of rhubarb has other ideas. It towers above the other local plant life and is often visible from miles away.  How does this strange, ethereal plant survive – let alone thrive – in this inhospitable environment? Its secret is simple but ingenious: it is its own greenhouse.

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You might mistake what you can see as a rather peculiar flower (once you get over the momentary panic that the triffids are having another day).  What you see is not a flower. The conical tower that is visible to the passing traveler is made up of translucent bracts. A bract is a specilaized leaf associated with the reproductive structure of a plant and they come in a multitude of shapes and sizes (often dependent on the plant’s pollinator).  In the case of noble rhubarb, these bracts create a translucent curtain which surround the stem and flowers contained within.

As such, they form a protective layer against the wind, the cold and ultraviolet radiation (which is higher at this altitude), acting to all intents and purposes like a tent.  However, sunlight can pass through these bracts which then creates a greenhouse effect inside, allowing the stem and flowers to grow and thrive at a much higher temperature than their surroundings.  The result is a microclimate which supports the plant’s growth and also attracts pollinators.

Of course, the pollinators are already cold-resistant. These insects (mostly blowflies, flesh flies and beetles) are especially adapted to the extreme alpine environment where more common pollinators like bees are scarce due to low temperatures and strong UV radiation.  However, think about it.  Given the choice, especially at night when temperatures plummet, would you rather huddle against a mountainside or take advantage of a tent that you have stumbled upon? So, as well as creating a shielded habitat for itself, the noble rhubarb attracts pollinators in search of some respite from the witheringly cold weather.

 

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Lifting the bracts reveals delicate, pink, papery stipules (which is the name for an outgrowth at the base of a leafstalk). Nestled within them are short, branched panicles bearing tiny green flowers. A panicle is a type of flower cluster with many small branches. Each flower usually has its own little stem.

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As the fruit matures, the once-protective bracts turn brown and start to drop off. The plant may appear lifeless, but it has one final task to perform. Rheum nobile relies on the wind to carry its seeds. It produces small, winged fruits known as achenes. These light, papery structures are easily lifted by the breeze, helping the seeds travel away from the parent plant to settle and grow in new locations.

If you look closely at the picture above, you can see the fruit ready to be taken by the wind.

 

At the end of the life-cycle, all that is left is the stalk, but the seeds have scattered, ready to begin the process again. Effectively, the noble rhubarb (Rheum nobile) has adapted to fill a unique ecological niche in alpine zones between 3,500 and 4,800 metres elevation in the countries of India, Pakistan, Tibet, Myanmar and Afghanistan.  The large, green leaves at the base of the plant (known as radicles) are often harvested to be boiled or stewed.  Like the rhubarb we know (and some of us love, especially with crumble and custard) these have a tangy flavour due to the presence of oxalic acid.  Once cooked and sweetened the bitterness is reduced, but it’s not to everyone’s taste.

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However, Rheum nobile is also part of traditional Tibetan and Himalayan medicine, often used to treat digestive issues, inflammation, or wounds. The dried root (which is incredibly hefty and often as long as the plant is tall) is sometimes ground into powder or steeped as a decoction (that is boiled for ages and then strained with the resulting liquid used either as a tea or for medicine).

Wait, there’s more. The stems of noble rhubarb contain a clear, limpid liquid, which can be drunk for refreshment during treks or herding in the high-altitude zones where it is found. As you can see, it's easy to spot. The water within is naturally filtered and mildly acidic. It is sometimes believed to have cooling or purifying effects, although this has never been scientifically confirmed.

As such, it’s useful to us in a number of ways.  That’s good news for us but bad news for the noble rhubarb. Its reproduction is sensitive to environmental pressures, including grazing by livestock like yaks, which can hinder its ability to produce seeds.  Plus overharvesting has made it scarcer than it once was - and it was never common by any means. Although the plant is not classified as endangered, botanists have noticed that its numbers seem to be in decline.  The old story – the more of us, the less of everything else…

Fingers crossed that the plant will persevere.  Let’s hope the noble rhubarb continues to astonish all who encounter it for the first time, for countless generations to come.

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