Category Archives: Nettle research

Exploring Brazilian karst in Tocantins

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Karst in Aurora do Tocantins, central Brazil comprising highly dissected outcrops with open vegetation, and collapsed forested margins. Credits, Alex Monro.

I have been interested in karst since a child. My Grandparents lived at the foot of a large outcrop in France where I spent much of my holidays exploring for insects, rocks and plants. Through my work on nettles, a group of plants very diverse on karst, I have become to think of karst as a forgotten domain for plants. One that has received little focus from botanists. Karst is weathered limestone, a rock produced from the shells of organisms that lived hundreds of millions of years ago. It is soluble in water and the action of rain in warm climates results can in a dramatic landscape of razor-sharp rocks, deep chasms and caves. Its porous nature, slow accumulation of soil and chemical composition makes it a challenging habitat for plants that can require significant adaptations that frequently results in a very specialised flora. Because of its porous nature karst is also a major source of underground water, on which ca 25% of the world’s population depend.

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Forested on collapsed karst in Tocantins with several outcrops visible in the distance. Credits, Alex Monro

Having explored karst in China for several years, where it is associated with a high diversity of rare species, I was very curious to discover how this compared with South America, whose karst has been little studied. To do so, we sourced plant collections data for Brazil, the country in South America whose karst has been best mapped and collected, and the we compared the number of species and their rarity to Brazil as a whole. The result was a publication [https://doi.org/10.1038/s41598-019-53104-6] which shows that, whilst an important source of plant diversity and rare species, in Brazil it is less so than the surrounding vegetation in which it is located. This suggests that there are some fundamental differences between the karst floras of South America and Southeast Asia and prompts several hypotheses to be tested. Before doing so, however, I thought that it would make sense to spend some time collecting in one of the least known but most dramatic karst landscapes in Brazil, in Tocantins state. These are formed from 600 million year old deposits exposed ca 120 million years ago, early in the evolution of flowering plants.

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Some of the plants collected in Tocantins. L-R, T-B: An unidentified and possibly new species of Apodanthera in the cucumber family; an unusual Aristolochia species in the birthwort family; a possible new species of Acanthostachys bromeliad. Credits, Alex Monro

Together with Pablo Hendrigo, Gabriel Marcuso and Julio Lombardi of the State University of Sao Paulo we spent ten days in the field. The fieldwork was great fun, with lots of climbing and regular botanical surprises. It was, however, very hot on the exposed outcrops and the rock itself weathered into very thin serrated leaves, blocks balanced on each other, with narrow chasms between them which made clambering across a nerve-wracking and exhilarating experience. We observed that the core of an outcrop often comprised an open cactus and bromeliad dominated desert-like vegetation, whilst the collapsed edges were forested. These deciduous forests were botanically the more interesting in that they were more diverse, and each had understory species unique to it. For example, the Acanthostachys and Aristolochia species above. The open vegetation of the outcrops shared most species with each other, most of which showed adaptations to the very dry and exposed conditions. Small piles of animal droppings indicated the presence of a large rodent, that we regularly glimpsed clambering over rocks. After a rainfall many fast-moving black and yellow millipedes and snails appeared. The snails seemingly grazing the lichen covered rock. In the time that we spent there we managed to explore a small handful of outcrops and I was left feeling that we had only scratched the surface.

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L-R, Gabriel Marcuso, Pablo Hendrigo and Prof. Julio Lombardi. Credits, Alex Monro

Strange world of fleshy nettle fruits (Urticaceae)

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Top: Myrianthus arboreus, Debregeasia salicifolia, Poikilospermum suaveolens. Bottom: Dendrocnide meyeniana, Urera baccifera, Touchardia latifolia.

Brightly coloured or fleshy fruit are not what you would associate with nettles. Indeed neither would most botanists who study them in a herbarium where once brightly coloured intricately shaped structures are reduced to congealed dark brown blobs. It is thanks to field work, and the enthusiasm of many amateur naturalists and their cameras that their beauty and complexity is becoming better known. Fleshy-fruited nettles are found across the family, comprising probably 1/4 of the genera. Nettles are very inventive in producing these fruits, with stalks, petals, fruiting branches or bracts being re-purposed following flowering. Although I work on nettles and so am naturally biased, I can’t think of another plant family that has come up with so many ways to produce a tasty morsel for a bird or mammal, or which produces such complex shaped fruits.

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Dendrocnide meyeniana, here brilliantly photographed in Taiwan by Flickr user ted762563. I have inserted arrows to highlight the tiny petals which later develop into the strange clasp-shaped fruit.

In the case of the tree from Taiwan and the Philippines, Discocnide meyeniana, the three tiny and unequal green petals around each ovary swell up into a ghostly white cradle which likely flags the exposed seed to potential dispersers. In this case likely a small bird. Another species with unusual fleshy fruits is a small tree from the Dominican Republic, Gyrotaenia microcarpa. In this species it is the fused flowering branches which become fleshy, expanding in fruit to leave the seeds exposed in small clusters on the outside, a bit like a misshapen strawberry.

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Gyrotaenia microcarpa fruit. The fused flowering branches swell up and become white, the seeds becoming black creating a contrast which presumably attracts small birds or mammals to feed.

In several species fruits designed to attract consumers also have stinging hairs. This is the case of the Latin American shrub Urera baccifera. In this species, not only do the tiny green petals become white and swell up to conceal the seed, but their flowering branches and stalks become bright magenta and fleshy, curling protectively over the white berries brandishing hypodermic stinging hairs. This suggests that not any animal is welcome to take the fruit. Whatever feeds on the berry will need to delicately free it  without getting stung.

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Urera baccifera, common throughout Latin America and well known for its brightly coloured but also stinging fruit clusters.

Probably the strangest looking fruit is that of Procris, a group of succulent species from Asia, the Pacific and Africa. In these plants the flower stalks all fuse to form a swollen foot. In fruit, together with the reduced petals at the ovary’s base, this becomes fleshy and when wet the whole structure is covered by a thick slime. It is hard to imagine what kind of animal this fruit is aiming to attract!

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Procris wightiana from Southeast Asia. The cup-like structures at the base of the seeds are the reduced petals that have fused and become fleshy.

 

I hope that this very brief and subjective survey of nettle fruits demonstrates how innovative and surprising plants (and nettles in particular) can be.

Lost world discovered in twilight of Chinese caves

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Elatostema obscurinervium growing in stalagmite drip zones, one of 31 species known only from caves in China and Vietnam.

I never expected to be working in caves, that is, until I started to study nettles in Southwest China with Guangxi botanist Wei Yi-Gang. When Wei suggested that we collect in a local cave I was not hopeful. However, that first visit transported me to another world, an eerie moonscape in which plants thrived in powdery ‘soil’ and perpetual twilight. I was immediately gripped and determined to explore as many caves as possible. Over the next few years we visited over 60 caves, travelling on underground rivers, hiking across rice fields or sneaking into big tourist caves. Each time I got the same thrill from entering these strange and silent places. This has culminated in a paper just published in the scientific journal PLOS ONE.

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Yangtse cave, Fengshan County, Guangxi. Eight species new to science have been described from here.

There has been very little research on plants in caves. Having come across such a widespread and diverse flora we wanted to make sure that both botanists and cave biologists were aware of it. This is because plants growing in caves could tell us a lot about how plants adapt to extreme conditions. Also, as to how connected caves are to the surrounding landscape and each other. To do so we set out to answer a series of questions. Probably the most obvious was, are plants growing in light levels distinct to those outside? Did the species evolve in caves? Or are they survivors of a previous vegetation that at some time connected caves? And, are these plants important for conservation in the region? For example, in the restoration of the karst forests lost during the 20thC.

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Cave converted to a tourist attraction.

There are thousands of caves in Southwest China and the landscape that they helped form has long been famous in Chinese culture and art. A landscape covered in dense forest until the 20thC at which time the ‘Great leap forward’ and later the ‘Cultural revolution’ resulted in massive deforestation. Once cut, the forest has not returned but instead been replaced dry scrub. The 21stC has brought new threats from cement and tourism. The rock that forms these caves is used to make cement, now in high demand, that combined with a rapid growth in tourism has meant once untouched ‘lost worlds’ are being mined or filled with walkways, bright lights and litter.

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Collaborators from the Guangxi Institute of Botany, Fu Longfei and Chen Xiaoqin taking photosynthesis measurements.

We found that some of the plants growing in caves are surviving in very low levels of light. Levels much lower than previously known. From other cave studies we also know that daily changes in temperature and humidity are very small. There is also some suggestion from other studies that the cave atmosphere may be richer in CO2. It could be that low levels of light are being offset by more stable conditions and higher CO2 – an interesting question for future research.

We also found that whilst most of the plants we document are known from forest habitats elsewhere, 31 species are only known from caves. For reasons given in our paper we do not believe that this means that they evolved in caves but rather that they are species which were restricted to the forests lost in the 20thC.

So, it looks as if the plants that we are finding in caves are relics of forests that were lost to deforestation in the 1950s and 1970s. With a current focus on restoring these lost forests in China, these surviving populations could now become a valuable source of local plant material for restoration.

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Yin Jia cave close to Gu Lin village in Yunnan. At 1600 m above sea-level this is also one of highest elevations that we have collected in caves.

Other posts by me on this topic

2016: Studying cave-plants in SW China

2014: Caves explored last month

 

Studying cave plants in SW China

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Yangtse cave, Fengshan County, Guangxi, type locality for eight species of plant. The plant-bearing part of the cave is ca 170 m deep and 70 m wide (note the person for scale)

As part of my research on the nettle family, Urticaceae I became aware of plants growing in the entrance caverns of caves several years ago and for over a year now my collaborators at the Guangxi Institute of Botany, China lead by Professor Yigang Wei and I have been working on documenting the full diversity of this unusual flora. This lead us to think about whether these plants may have become adapted to life in caves, in particular the relatively constant climate and low light. Especially for species which grow amongst the lowest light levels at the back of caverns where they are growing in a fraction of the light they could be expected to receive in a forest. We therefore applied for a grant from the Guangxi Key Laboratory of Plant Conservation and Restoration Ecology in Karst Terrain, and the Foreign Experts Bureau to undertake some preliminary work to document the climate, light and photosynthesis of the plants in the caves.

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Fu Longfei and Chen Xiaoqin taking photosynthesis measurements using an instrument called a handheld PAM which uses fluorescence to measure various aspects of photosynthesis.

We selected the Yangtse cave as we know the diversity of plants that grow there (ten species of nettle alone), we have three data-loggers recording temperature and humidity in it and it is close to a town where we can spend the night. It is also a spectacular and beautiful place to spend several days working. The aim of our work was to collect the data necessary to test the hypothesis that the plants growing within the entrance cavern of the Yangtse cave exhibit different photosynthetic performance than the same or congeneric species growing outside of the cave. To do this we randomly selected individuals of three species of nettle in the genus Elatostema, one species of Begonia and a species of fern at four different locations in the cave, the back, midway into the entrance cavern, at the entrance and outside of the cave. We also brought two species of Elatostema from the living collection at the Guangxi Institute of Botany to compare their photosynthesis performance with members of the same species that had grown up within the cave. This was to get some indication as to how plastic their response was.

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Elatostema obscurinervium, one of 31 species known only from caves and recently collected from a cave in northern Vietnam.

Each plant was connected to a hand-held PAM chlorophyll fluorometer, an incredibly sensitive device that can measure several key outputs of photosynthetic reactions in the chloroplasts as they take place. By comparing our study plants to those growing outside of the cave and from the scientific literature we hope to see whether cave-dwelling plants differ from non-cave plants in some of those parameters, and whether those differences are dependent upon what kind of plant they are. These parameters include the efficiency of photosynthesis, that is how much of the light energy is harnessed by the photosynthetic reactions, how much is dissipated and how resilient the photosynthetic apparatus is to changing light intensity. If we find  a difference between cave and non-cave dwelling plants then taken together these measurements can provide some indication of which group of photosynthetic reactions are leading to these differences.

Exciting images of nettle flowers

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Partially dissected female flower of the subtropical shrub, Pouzolzia zeylanica showing the ovary exposed (left) and the elongated style and stigma (right) protected by tusk-like hairs. Image by Jia Dong, RBG Edinburgh

Working with Royal Botanic Gardens, Edinburgh student Jia Dong and plant anatomist Louis Ronse De Craene has resulted in some exciting and thought-provoking images of nettle flowers. The aim of our collaboration is to understand how nettle flowers develop and in the process work out what parts they have in common and which they don’t. The samples used were from living collections at Edinburgh and RBG Kew, together with my own collections in alcohol made over several years. The results are some beautiful and very informative scanning electron micrographs which show that the part of the female flower which recieves pollen (stigma) and conducts it to the egg (style) is characterised by two classes of hairs, one comprising defensive tusk-like hairs (above) and the other receptive tubular like hairs (above & below).

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Stigma hairs at the tip of the ovary of Pilea grandifolia, a succulent herb from Jamaica. Stigma hairs in the nettle family are characterised by their rounded obtuse tips and cylindrical shape. Image by Jia Dong, RBG Edinburgh.

Tubular hairs associated with the stigma are characteristic of all nettle flowers. They also appear very early in development. Combined this makes us think that they might have a role in pollination. Specifically in the reception of pollen. Being wind-pollinated, nettles don’t have a lot of control as to whose pollen reaches their female flowers and so there needs to be a way for them to control which pollen grains develop and fertilise the single egg. It seems likely that these hairs play a role and hopefully Jia will be able provide some more great images to test some hypotheses about this.

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Female flower of Cecropia sp., a tcommon ropical tree from the Americas. In addition to stigma hairs you can see an apparent fold in the ovary. Image by Jia Dong, RBG Edinburgh.

 

Herbarium visit to La Paz (LPB)

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The sorting bench where incoming material is identified in the La Paz (LPB) herbarium

One important task for specialists in a particular plant group, in my case nettles, is to visit national or regional collections and not just rely on the collections of our own institutes, no matter how good they are. As part of a conference and field trip I have just spent a couple of days in the La Paz herbarium. My colleague Nicholas Hind will spend three weeks there identifying plants from the daisy family (Compositae) and running an identification course. There were 92 boxes of unidentified Compositae waiting for him when we arrived!This herbarium was founded by German botanist Stephan Beck in 1984 and currently houses over 400,000 herbarium specimens. The reason why such visits are important both for the specialist but also for the herbarium are that although there is an active inter-herbarium loan system for plants it relies on material being accessioned, mounted and identified. This can be a real challenge to achieve in a country where there are few funds and even fewer botanists. The visit of a specialist allows material that has not been mounted or accessioned, together with unidentified material, to be reliably (one hopes) identified and so used as reference for future identifications. Continue reading Herbarium visit to La Paz (LPB)

Working on Cuban nettles in Berlin herbarium

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A Cuban species of nettle, possibly undescribed. The leaves are about 2 mm across. To the middle right of the picture you can see a small cluster of female flowers about 1/2 mm in length

Funded by the Synthesys project I am studying the Cuban nettle collections of the Berlin-Dahlem Museum. The aim is to finish my account of the nettle family for the Flora of Cuba project that I started five years ago. It might seem odd that Cuba has so many nettle species that I can still be working on it, albeit in a fragmented way, for five years. Also that Berlin should be an important repository of Cuban plants, but there is a reason.

Cuba has an exceptionally rich flora and is especially important for the nettle family, Urticaceae, which is represented by about 70 species in eight genera. Together the Greater Antilles, Jamaica, Haiti/Dominican Republic, Cayman Islands and Puerto Rico, is a centre of species-richness for one group of nettles in particular, the genus Pilea. There are over 150 species of Pilea in the Greater Antilles, 60 of which are native to Cuba. The reason for such high diversity is unknown but may have something to do with the age of the islands, preponderance of limestone substrates or something else that we haven’t thought of yet. It does, however mean that I have been spending a lot of time looking at herbarium spcimens of this genus in the Berlin herbarium.

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Room K10 in the underground, bomb-proof Berlin-Dahlem herbarium. This is where the Cuban collections are stored

The connection between Germany and the the Greater Antilles started with botanist Ignatz Urban, who did a  lot of work documenting the plant diversity of the Greater Antilles. Tragically most of his collections were destroyed in World War Two when the herbarium was bombed. During the Cold War the connection that had established between Berlin and the Caribbean switched to East Germany and the Jena herbarium impulsed by the formidable Johannes Bisse who founded the National Botanic Garden of Cuba. This lead to the foundation of the Flora of Cuba project a collaboration between the many excellent Cuban botanists and their German counterparts, initially in Jena and then from 1993 in Berlin. So that is the reason that I am in Berlin looking at Cuban nettles!

Ghost flowers in the nettle family

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A pickled Flower of Boehmeria zollingeriana, 1.2 mm in length viewed under a Zeiss Axioskop microscope. You can clearly see the two stigmas (ling filament like structures) and if you look carefully the two overlapping eggs within the ovary (dark egg-shaped structures)

Nettles are characterised, amongst other things, by having flowers with a single egg in their ovary and a single stigma, the structure which conducts the pollen to its target. Work by developmental biologists almost a century ago suggested that the ancestor of nettles probably had two eggs per ovary after discovering that at a very early stage of development nettle ovaries contain two eggs one of which disappears as the flower develops resulting in the single egged flower which characterises the family. It was therefore a great surprise when plant collections from Costa Rica examined in the 1990s were found to have flowers with two or three eggs and stigmas per ovary. These very unusual plants were described as a new species: Boehmeria burgeriana  by colleagues Melanie Wilmot-Dear and Ib Friis. Continue reading Ghost flowers in the nettle family

Soleirolia, a genus of small but perfectly formed nettles

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Close-up of a flowering stem of Soleirolia soleirolia showing the male (left) and female (right) flowers. The leaves of this tiny creeping herb are about 3 mm across

I first came across this tiny creeping herb in my garden where it had been planted as an ornamental. The bright green leaves, mostly less than 3 mm across form an attractive carpet. Until now I had never been able to spot its flowers despite having checked several times over the last few years. My guess is that this species has a relatively narrow flowering time in spring and the flowers are so tiny that they are only visible with a hand-lens. For several years the genus has intrigued me, not so much because of its small size and creeping habit but because of its distribution and evolutionary relationships.

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Engraving  of a female Soleirolia flower produced by the Anglo-French botanist Hugh Algernon Weddell in the 1850s. Weddell must have had access to microscopes of the very highest quality to produce such a drawing as the flowers that are about 1.5 mm in length

Firstly because Soleirolia consists of a single species that in the wild is only known from the Mediterranean island of Corsica. This is the only genus of nettle I know that is restricted to a single island or to the Mediterranean and I am very keen to try and found out why this could be (the history of the Mediterranean basin is quite a turbulent one). Secondly Soleirolia has traditionally been grouped with the  widespread Parietaria and intriguingly with Gesnouinia,  which also includes a single species but is restricted to the Canary Islands in the Atlantic Ocean. Whilst they look very different as plants their female flowers share many similarities of form.  It might be, therefore, that Soleirolia and Gesnouinia should be viewed  as Parietaria species that have diverged morphologically as a consequence of being isolated on islands, a common phenomenon in evolutionary biology. I am currently testing this possibility using DNA sequence data and could have a better idea in a couple of months.

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Endemic to Cosrica but now an ornamental and escaped weed throughout much of the temperate World Soleirolia soleirolia forms bright green carpets of tiny leaves

 

 

Seminar at the Royal Botanic Garden Edinburgh on the nettle family

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View of the tropical glass house at the Royal Botanic Garden, Edinburgh

Last week I was lucky enough to be invited to present a seminar on  the nettle family, the Urticaceae at the Royal Botanic Garden Edinburgh. I have been working on this group of plants for over fifteen years with various collaborators  and am finally ready to publish a revised classification of the family. I had a good audience who asked some insightful questions as well as making some good suggestions for future research. You can see a pdf of my slides by clicking on the following link: Edinburgh Urticaceae 19-6. Afterwards I had a chance to talk to a number of colleagues that I would like to start collaborating with in the future.