Caves explored last month

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Yin Jia cave close to Gu Lin village in Yunnan. This is the 37th cave we have explored. At 1600 m above sea-level this is also one of highest elevations that we have collected in caves. Click to see a clip of the cave entrance

Thanks to funding from the Bentham Moxon Trust and the Guilin Botanical Garden, myself and colleagues explored five caves for plants in October of this year (2014). There are likely thousands of caves in the limestone karsts of south-east asia which contain plants. Whilst of great interest botanically and for conservation they are also beautiful in their own right and each cave is unique. I thought I would provide a portrait of each one to show how varied they are in their form, where plants grow in them and their size.

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Cave #40. We spotted this cave from the road and getting to it involved climbing onto an aquaduct that ran along the base of a large cliff and then jumping off into the cave. The elevation of this cave is 660 m above sea-level and it is located in the province of Guizhou.

The cave above was one of the few that we spotted from the road and then were able to get to. It is also one of the few that had little evidence of human disturbance, very few footprints and areas of pure white travertine that had fallen from the roof had not been walked on or collected. The main plant-bearing cavern of the cave was about 25 m deep and the roof 15 m high and it had a well developed flora, you can see plants from the african-violet family (Gesneriaceae) in the foreground and we collected five species of nettle here.

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This is the enormous Xiangshuidong Tian Keng cave in Guizhou, known to us as cave#38. Click to see a panorama from within the cave

Xiangshuidong Tian Keng cave in Guizhou was one of the largest caves that we have collected in, but also one of the most impacted by tourism and use by local communities. The main cavern is about 250 m deep with a roof between 45 and 30 m high and it is set within a huge cliff forming the side of a mountain. It also has a waterfall and river running across the back of it. It is in this cave that we found a very rare and unusual form of Elatostema oblongifolium that has its male flowers borne on specialised shoots but overall the plant diversity of the cave was quite low, presumably because of the large numbers of local tourists and associated trampling of much of the ground available for plants

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This is Cave #36, Yuen Ja cave close to Mahi Po Niochan village in Yunnan. The cave has two main chambers, each with their own entrance and which come together at their back where a new and unexplored chamber continues on. Each of the main chambers is 30 to 40 deep and the entrances 3 to 6 m high.

This was the first cave that we encountered on this field trip. We found it after first being taken to a hole in the ground as what must have been a mistranslation from Mandarin into the local dialect. The cave was relatively big and had a trail running inside. The main cavern shelves very steeply meaning that very little light penetrates into the cave. Despite this and the relatively high altitude, 1500 m, we collected seven species of nettle from here.

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Unfortunately I didn’t record the local name of this cave so it is known only as Cave 39. It is in the province of Guizhou at an elevation of 600 m. The main cavern was about 40m deep and  the entrance about 10m high and 30m wide. Click to see a panorama of the interior of the cave.

This cave should have been perfect as it shelved gently meaning that light penetrated quite deep, it also had plenty of places for plants to grow, such as boulders and rocks. We only collected four species of nettle here, probably because the cave was heavily impacted by farmers using it as a barn to keep their water buffalo in at night. Evidenced by lots of hoof prints and dung. This is a very common use of caves and the trampling of buffalo and their herders can have a significant impact on the plants in the caves (see below).

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Staminodes in nettles, an elegant use of ‘spare’ parts

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Fruit of Pilea japonica, ripe seeds are black and at their base you can see some white structures folded in on themselves. These are the modified stalks of remnants of male flower parts

Nettles have unisexual flowers, that is each flower functions only as a male or a female. Counter-intuitively though the flowers still retain the non-functional and often much-reduced organs of the non-functional sex. These are called pistillodes in the case of the rudimentary female organs in male flowers and staminodes in the case of the rudimentary male organs in female flowers.  In part of the nettle family the staminodes are put to good use: ejecting the seed from the fruit.

Male flowers of Elatostema nanchuanense (left) showing the male flower parts, a pollen sack borne on a stalk and left their modification in the female flowers of the same species

This can be best understood by considering that nettles have male flowers which open explosively, pollen being released in tiny clouds (they are also very small). In fact one species, Pilea microphylla, is commonly known as the artillery plant for this reason. The mechanism for the explosive opening of the male flower is that the stalks (filaments) of the pollen sacks (anthers) are folded in on themselves in bud. As they develop these stalks fill with water until they are all pressing against each other within the flower bud and ready to burst. At a certain point the pressure becomes too great for the thin petals of the flower bud and they rip leading to the stalks being able to straighten explosively. This has happens incredibly quickly and although it has not been recorded for nettles, in the closely related mulberry where this also happens, the flower can open in 25 millionths of a second, moving petals to velocities in excess of half the speed of sound.

Elatostema nanchuanense showing the fruiting flower head with staminodes, fruit and an ejected seed indicated by yellow arrows

In one group of nettles which includes seven genera this explosive ability of the pollen sacks has been harnessed to release the seed from the fruit. Below you can see a close-up of the fruit of Pilea japonica showing the staminodes flexed and ready to eject the seeds (dark coloured).

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Two weeks collecting in caves and gorges in South China

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Very steeply sided hills characteristic of limestone karst. This limestone was first exposed ca 240 million years ago and the karst produced by the action of rain over tens of millions of years

I have just returned from collecting nettles in South West China with my great friend and colleague Professor Wei Yi-Gang and researcher Fu Long-Fei from the Guilin Botanic Gardens. For several years we have been working on documenting the nettle diversity of the limestone karst of this region, focusing on the poorly known cave-associated floras. Karst is a form of limestone which has been weathered by rain for millions of years resulting in finely divided and sharp surfaces and very steeply sided hills, small mountains and gorges. The karst where we have been working form part of a formation which runs from Myanmar, northern Thailand and Vietnam and across into southern China and includes the famous ‘stone forests’ of Yunnan and Guangxi. I am interested in karst because it is where nettles are most diverse, both in terms of genera (species groupings) and species. At a single location it may be possible to encounter eight genera and over a dozen species!

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Yuan Jiá cave in north-eastern Yunnan close to the border with Vietnam at an elevation of 1500 m, we collected five species of nettle from this cave. Click on picture to see me introducing our work outside of the cave

Because the limestone is porous it has resulted in the formation of thousands of caves whose entrances have been colonized by plants from a small group of families: nettles (Urticaceae), african violet family (Gesneriaceae), Begonias (Begoniaceae), ivy family (Araliaceae), the coffee family (Rubiaceae) together with ferns and mosses. The most diverse of these are the nettles, one group of which, Elatostema has about 1/5 of the species from this region known only from caves. As well as having very low light levels, sometimes 1/10 of 1% daylight, the caves have constant humidity and low temperatures which contrast strongly with the cave exterior. The cool air of a cave can be felt up to 20 m from the entrance, often before the cave itself can be seen. We believe that the species associated with caves have likely come from the deep shade of the forests that once dominated this area but which have since been lost to agriculture. It also possible that some of the species are relicts of a previous, cooler climate during the last ice-age. This is something that we have begun to study.

Elatostema binatum, one of over 15 species of Elatostema known only from caves in Guangxi, Yunnan and Ghuizou. This species is unusual in bearing male flowers on young shoots, female flowers have never been seen!

Caves represent a last refuge for several hundred species in SW China and now is a time of great change as caves come under threat from tourism, agriculture, urbanization and cement production. We want to help conserve these caves and the species that they include by first documenting their diversity and distribution across SW China. This information can be disseminated within China in the hope of raising awareness and protecting individual caves. It could also be used to identify a network of protected caves which include all of these species. Professor Wei would also like to develop protocols for cultivating the species outside of caves, something that is very difficult to achieve at the moment and which could represent a vital step for their conservation.