Tuesday, 19 December 2017

Another parasite for Christmas, Cistanche


This being my last post before Christmas Day it's time to talk about parasites. Not those that visit you around this time of year in search of gifts and hospitality, but plants that survive off the 'generosity' of others. I've blogged about a few of them already.

The kiss-inducing mistletoe (Viscum album) is a parasite, or partly so. We call it a hemiparasite in recognition of it producing its own sugars through photosynthesis, but drawing most of its water and nutrients from the host plant.


The Western Australian Christmas Tree, Nuytsia floribunda, does the same. These hemiparasites can be attached to roots or stems. Other mistletoes are fully parasitic, such as the leafless Tristerix aphyllus growing on cactus stems.

The tiny Christmas Lantern, Thismia, is parasitic on fungi and grows entirely under the leaf litter - flower and all. Due to its obscure habit, it is unlikely to adorn a festive table, although its flower is a Christmassy red colour.

This next one isn't so beautiful in form or colour. It's the Lesser Broomrape, Orobanche minor, photographed here in the Melbourne Gardens, in early November.


The Orobanchaceae is a relatively large family (around 2000 species) of root parasites, many - such as this one - having no chlorophyll (so no photosynthesis and entirely dependent on their hosts). The Ivy Broomrape, Orobanche hederae, was one I saw commonly in the UK, and this Lesser Broomrape pops up here and there around Melbourne and much of southern Australia.

There are 140 species of Orobanche with only a variety, of Orobanche cernua, native to Australia. The Lesser Broomrape (above) was introduced into Australia from Europe, presumably inadvertently as cargo on one of its many hosts. In this case it seems to be attached to the roots of a Plectranthus.


But today I want to make special mention of a weird desert plant called Cistanche. This genus came to my attention most recently in a talk at the Chinese Association of Botanic Gardens meeting in Chongqing, China, in October. Unfortunately the presentation was in Mandarin but I could at least marvel at the photographs (the image above shows a warty underground stem, the picture at the top of the post, Cistanche deserticola in flower).

The genus extends from Europe into Asia (or vice versa...), with five species native to China. Medicines are extracted from a few of the Chinese species but Cistanche deserticola ('desert loving') is the mostly commonly used: the Flora of China states that "the stems are used medicinally for enriching the blood, invigorating the kidney and strengthening yang sexuality, and relaxing the bowels". It has become increasingly popular in recent years as an aphrodisiac, and more recently, shown to have potential as an anti-colon cancer therapy. 


I gathered from the visuals in the talk that Cistanche deserticola, or Desert Broomrape, is grown extensively in dry parts of China. It was planted in long rows, near to and perhaps parasitic on a plant that looked like Tamarisk (Tamarix) but was more likely to be Saxaul (Haloxylon ammodendron).

Huge quantities - there were lots of massive numbers and illustrations of harvest bounty - of the root are used for medicines. An annual conference is held each year in China to discuss the genus and its cultivation. 


A newspaper article from China in 2009 argued that cultivating and harvesting Desert Broomrape made the planting of Saxaul economic. Saxaul is a drought-resistant shrub used to stabilise sandy deserts in western China. However without the money brought in through the Broomrape, there is no financial incentive, or ability, to plant Saxaul.

Due to my linguistic limitations I don't know the full environmental and economic consequences of this kind of farming but Broomrape is clearly big business in China and the rows upon rows of pine-apple-like flowering stems are impressive. I just wished I'd taken more pictures during the talk.

Anyway, Merry Christmas or happy festive season, and may your bowels be relaxed and all other desires satisfied.

Images: the top image is from Urbol, the picture of the harvested root from Rainbow, and the Christmas mistletoe, from The Sun.

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