A study of Toothwort, Lathraea squamaria, in Old
Sulehay
Nick Owens
A preliminary study was made of toothwort in Old Sulehay as this is one of the key plant species in the reserve and any management should take account of its distribution and ecological requirements. Toothwort is described by Gent and Wilson1 as ‘very rare’ in Northamptonshire. It is listed from Old Sulehay Forest, Fermyn Wood, Bedford Purlieus, Castor Hanglands and Wakerley Wood. Rees2 describes toothwort as ‘quite frequent’ in Old Sulehay Forest, and to be ‘parasitic on hazel, sycamore, elder etc’. Morton Sale is mentioned as an additional site.
A hand held GPS was used to map the positions of all toothwort found in the forest, an attempt being made to cover the whole forest by wandering back and fore, searching the ground. The GPS is nominally accurate to 1m, giving a 5 figure read-out, but accuracy is probably not quite this good. The survey was done between 22/4/03 and 4/5/03, by which time the toothwort was fruiting. The mapped plants were plotted by Mike Rogers using ‘Map Maker’ software on outline maps of the reserve which he created using a similar GPS. For all colonies of toothwort found, the following details were recorded: a) the total number of flower spikes b) the nearest woody tree species and its distance from the nearest toothwort c) the percentage cover of bare ground in a 1 metre square around the centre of the toothwort ‘colony’ (ie clusters of flower spikes around one host) d) other herbaceous plant species present in the 1 metre square.
Where is toothwort found in the forest?
Click here to view a map showing the distribution of toothwort colonies in the forest. The majority of plants are in the eastern, damper area of the forest, but there are also significant amounts in the southern part of Kings Oaks. There were undoubtedly a good number of colonies missed, but none could easily be found in Cow Wood or the central area of the forest.
Which host species were used?
The commonest host was hazel, with maple also being quite a common host, especially in Kings Oaks (Table 2). There were many apparently suitable hazels and maples without visible colonies. It is not known whether all colonies flower every year. In the New Atlas3 toothwort is described as ‘annual or perennial’.
Table 2. Host species of toothwort
|
Host
species |
No. |
% |
|
Hazel |
22 |
67 |
|
Hawthorn |
2 |
6 |
|
Field
Maple |
8 |
24 |
|
Elder |
1 |
3 |
How many flower spikes were there in each colony?
Thirty three colonies were found and studied. The number of
spikes per colony varied from 1 to 27. The mean was 11.12, s.d. = 8.88. Many of
the spikes were touching or very close to the base of the trunk, and most were
within 0.5m. In one case the nearest woody plant was a hawthorn 1.5m away, and
in another case an ash 0.5 – 2.0m from the toothwort. This ash was is not
included in the list of host plants below as there was no other evidence that
ash was a host. Ash is listed as a host species in the New Atlas3.
The majority of specimens were adjacent to living plants, which is consistent
with a parasitic lifestyle.
Does toothwort prefer bare ground?
The percentage of bare ground (ie either bare earth or a carpet of dead brown leaves) varied from 0 to 95%. The mean was 48.8%, s.d. = 30.05, n = 33. By hunting among the dog’s mercury around hazel trunks, some toothwort was found, apparently in a healthy condition, where there was no bare ground at all. As toothwort requires no light for photosynthesis it may not need much open space, and the common impression of its being most abundant on bare ground may be mistaken. Pollination requirements may be significant however (see below).
Which herbaceous plants were associated with toothwort?
The plant species occurring within an area of 1m2 around the centre of each colony were as follows:
|
Plant species |
Total sites (n = 33) |
% sites |
|
Dog's mercury |
27 |
82 |
|
Wood anemone |
15 |
45 |
|
St John's Wort |
1 |
3 |
|
Cuckoo pint |
5 |
15 |
|
Nettle |
2 |
6 |
|
Bluebell |
13 |
39 |
|
Celandine |
3 |
9 |
|
Ash seedling |
1 |
3 |
|
Maple seedling |
1 |
3 |
|
Ramsons (garlic) |
2 |
6 |
Toothwort has a distribution which largely overlaps the distribution of wood anemone, which is in the damper, eastern end of the forest. The prevalence of dog’s mercury near toothwort reflects dog’s mercury’s abundance throughout the forest. At first it was suspected that there was no toothwort among the ramsons patches, but on closer inspection some was found, and other hidden colonies may have been missed. The part of the forest invaded by sycamore held hardly any toothwort, though one spike was found adjacent to elder by the badger sett. The flower spikes on maple in Kings Oaks were rather small, possibly because of lack of water. Toothwort is largely absent from the drier counties in East Anglia, though it is also scarce in the most westerly extremities of Britain3.
Only one pollinating insect was observed visiting toothwort – a queen Bombus pratorum on 23rd April. By 4th May most spikes had set seed, and the swollen fruits were protruding. The fruiting spikes had died down by the end of May.
The species’ confinement to ancient woodland suggests a limited ability to disperse. No evidence was seen of seeds being eaten by mammals or birds and this would repay further study. It does not seem to be known whether toothwort is an annual or a perennial3. It certainly seems to reappear at the same place in successive years, but this could be either from seed or from organs of perennation.
Toothwort is abundant in Sulehay Forest, especially in the eastern part. A return to coppice management may not be harmful to it, and some specimens seemed to be thriving in the coppiced ‘scallops’, especially in the ditch beside the wood bank. However, it would seem incautious to coppice a large area of the eastern sector of the forest. Removal of the sycamores would, however, not cause it significant harm as only one specimen was found in the sycamore area. Sycamore saplings are invading areas of hazel where toothwort occurs, but most have now been removed. Sycamores may dry up the ground too much for toothwort to thrive. The exact ecological requirements of toothwort need further investigation and should include long term studies of individual colonies.
1. Gill Gent, Rob Wilson et al. 1995. The Flora of Northamptonshire and the Soke of Peterborough p. 222. Robert Wilson Designs.
2. Rees, John S. 1970. A Flora of Oundle, p.99. Oundle School Natural History Society.
3. Preston,C.D, Pearman,D.A and Dines,T.D. 2002. New Atlas of the British and Irish Flora p.576. Oxford University Press.
