Tag Archives: Nettles

Studying cave plants in SW China

DSCF6421.JPG
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.

DSCF6361.JPG
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.

DSCF6334.JPG
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.

A likely new species of Pilea from the Dominican Republic

am7464 P1040445
A possible new species of Pilea characterized by large tubers which probably enable it to survive in fissures in limestone karst cliffs where it grows. Image Alex Monro.

On my recent trip collecting nettles in the Dominican Republic we came across what is very likely a new species of Pilea, a group of about succulent nettles. I thought it might be useful to outline what happens from collecting / discovering something new to it being published as a new species, from my own botanical perspective of course. In the case of this species, it has a couple of distinctive features which make it stand out from similar looking Pilea species: 1) a well developed above-ground tuber, up to the size of a small potato, and 2) relatively large male flower clusters for the group of species it is in. This gives me two diagnostic characters to check with in existing collections and in the literature. Pilea is a genus of over 700 species found in tropical and subtropical Asia, Madagascar, Africa and the Americas. All but a few species are restricted to one of these areas or a much smaller area and this knowledge enables me to delimit my search area. In this case, the Greater Antilles (Cuba, Jamaica, the Cayman Islands and Hispaniola).

am7464  DSC_2082
Close-up of the leaves and flowers. The cluster of red flowers on the left are male and are borne on a relatively long stalk, to the right you can see a cluster of female flowers. This cluster is only a few mm long and contains several flowers.

My second job is to see if the species has already been described. To do this I need to look through the collections of the most appropriate herbaria for this area, starting with the National Herbarium of the Dominican Republic. This can take quite a long time although many collections have been digitised and are available online. I then need to follow this up by reviewing the literature for the region to see if I find any descriptions which match or are close. Once I have done this I should have a list of species that are possible or close matches. These I can then compare in more detail with my possible new species and confirm whether it is new or not. This I will do by looking at the type specimens under a microscope and comparing their key features: leaf and stem shape, the nature of their hairs, the size and shape of the flowers and of course in this case, the presence or not of a tuber. This also provides me with the information I need to write the diagnosis of the new species. Once I am sure that this is a new species I can start writing the description and think of a name. A new species description will include a detailed description of the plant, a line drawing illustrating the diagnostic features and a species conservation assessment which will provide an indication as to how threatened with extinction it is.

am7464 P1040455
A cross-section through one of the tubers. The tuber likely serves as a water storage device to help the species survive dry periods growing in narrow fissures in rock.