Thursday, 3 March 2011
This antisocial poisonous plant clone is not for sale
I took a stroll in our local woodland yesterday and was surprised to see how much had changed in a couple of weeks. Everywhere new green vegetation is pushing through as the snowdrops fade. Most notable are the Lord’s and Ladies (Arum maculatum) and Dog’s Mercury (Mercurialis perennis). Interestingly both of these species are reputed to be poisonous to animals, perhaps defending themselves as early emergers from the onslaught of grazing. However for Dog’s Mercury the evidence appears limited and contradictory. Watson (1998) describes suspected poisoning in cows, but such reports are rare and there are reports of animals happily grazing on the plants such as Muntjac deer. Interestingly it is also used in remedies for medicinal purposes, such as the ointment, ‘Wound-Care’, used to help accelerate wound healing (Weleda, 2009).
Dog’s Mercury is dioecious (=two forms) with clearly different male and female plants, in particular the floral parts (the plants in the image are male, showing catkin like spikes emerging from leaf axils - Rose, 2006). However this species expands mainly asexually by vegetative propagation, with rhizomes extending underground and sending up frequent aerial shoots. This produces large single sex clonal stands which appear to remain quite distinct, rather than mixing with adjacent ones (Wilson, 1968 – cited in Jefferson, 2008). Have a look and observe that most patches are distinctly male or female. Improved light conditions (such as canopy openings in woodlands) appear to favour male plants (Vandepitte, 2009b) which may exaggerate their separation from females.
Although it is a widespread and common plant in woods and shady places, its distribution appears to be limited by a strong affinity to ancient woods in Britain (Peterken & Game, 1981). There is also evidence of local declines through factors such as increasing deer browsing (Hall, et al. 2004), coppicing and other disturbance that opens up woodland canopies, bringing increased competition from other plant species. So with poor mobility and growing threats, it is probably declining gradually in parallel with the loss of older and precious ancient woodland (Grimes et al, 2007). So please look again at this apparent modest plant and see it as an indicator of the health and heritage of our woodlands which should not be put up for sale to the highest bidder.
Hall, J.E., Kirby, K.J & Whitbread, A.M. (revised 2004) National vegetation classification field guide to woodland. Joint Nature Conservation Committee.
Grime, J.P., Hodgson, J.G. & Hunt, R. (2007) Comparative Plant Ecology: A Functional Approach to Common British Species, 2nd ed. Colvend, UK: Castlepoint Press.
Jefferson, R.G. (2008) Biological flora of the British Isles: Mercurialis perennis L. Journal of Ecology, 96: 386-412
Peterken, G.F. and Game, M. (1981) Historical Factors Affecting the Distribution of Mercurialis perennis in Central Lincolnshire. Journal of Ecology, 69 (3): 781-796.
Rose,F (2006) The Wild Flower Key – How to identify wild flowers trees and shrubs in Britain and Ireland. London: Penguin Books Ltd
Vandepitte, K., Roldán-Ruiz, I., Leus, L., Jacquemyn, H. and Honnay, O. (2009b) Canopy closure shapes clonal diversity and fine-scale genetic structure in the dioecious understorey perennial Mercurialis perennis. Journal of Ecology, 97:404–414
Watson, P.J. (1998) Suspected dog’s mercury (Mercurialis perennis) poisoning in cattle. Veterinary Record, 142 (5): 116–117.
Wilson, J.F. (1968) The control of density in some woodland plants. PhD Thesis, University of Lancaster, Lancaster, UK.
Weleda (2009) Wound-Care [online]. http://usa.weleda.com/our-products/shop/wound-care.aspx [Accessed December 17th 2009]