Northern Ireland's Priority Species

Dencoeliopsis johnstonii – a fungus

Dencoeliopsis johnstonii

Dencoeliopsis johnstonii (Berk.) Korf
Family: Helotiaceae

This is a rare cup fungus that parasitises other ascomycete fungi on birch trees. It is a genuinely rare species across Europe.

In brief

  • The only record for this species in Northern Ireland is from Ballynahone Bog in October 1997

  • There are only five records from the British Isles, two from the 1800s, one unspecified from the 1900s, the Northern Ireland record from 1997 and a record from Surrey in 2002

  • It parasitises other fungi and is only found on birch

  • This is a rare species, even across Europe

  • As the two modern records are from downy birch surrounding a bog, the threats could be site management leading to the removal of the trees.

Species description
This is a small cup fungus that can be up to 4mm in diameter with a short stalk. The cup can be yellowish when young but is usually brown in colour. The outer surface can be scurfy. It is an ascomycete or spore shooter that shoots its spores upwards away from the fruiting body rather than a basidiomycete fungus whose spores fall down with gravity from gills, spines or pores. It parasitises other ascomycete fungi. In the British Isles, the species with which it has been recorded is Xenotypa aterrima and if this is the case, it is seen fruiting on a black lumpy crust on a birch branch (Xenotypa aterrima) which has its bark peeling back. In France, it has been recorded with Atopospora (Euryachora) betulina which resembles a black tar spot found on dead birch leaves (see Although not recorded from Northern Ireland, this is a much more common fungus than Xenotypa aterrima, although the majority of its records are pre-1970. To date, D. johnstonii has not been recorded from this substrate in the British Isles.

Life cycle
It was recorded in Northern Ireland in October. However, some books (e.g. Nordic Macromycetes Vol.1) describe it as a spring species. The October collection was long past its best and it may have first appeared in late summer.

Similar species
There are many species of cup fungi, but there are few other species of this size (most are smaller) from birch wood or leaves, especially growing out of black crusts or tar spots on the branches or leaves. Most cup fungi, however, need microscopic examination to confirm their identification and the size, colour and form of the spores need to be checked along with other microscopic characteristics.

How to see this species
The only record of this species is from the birch woods surrounding Ballynahone Bog in County Londonderry, in October. As it is typically found associated with X. aterrima which causes the bark of the branches to peel back, this can be quite noticeable and possible trees can be scanned for this character. Xenotypa aterrima has been found (commonly) at Derryadd Lough in Peatlands Park in County Armagh, as well as at Ballynahone More. Relevant access permissions should always be sought prior to visiting any sites.

Current status
The only record of this species in Northern Ireland is from the birch woods surrounding Ballynahone Bog in County Londonderry. It is genuinely rare across Europe, for example, being listed on the Danish Red Data List.

Why is this species a priority in Northern Ireland?

  • Rare, only occurring at Ballynahone Bog in Northern Ireland. This is its only Irish record and one of only two post-1970 records for the British Isles.

Threats/Causes of decline
As this species seems to be found on birch around raised bogs, site management aimed at clearing trees supporting this species is the main threat. Prior to any clearance of downy birch, a check should be carried out for the presence of this species. At Ballynahone More it was found on fire-damaged birch. At Derryadd Lough, the host Xenotypa grows on both fire-damaged and on undamaged birch. These are always fairly isolated young trees and Xenotypa has not been found in dense mature growth. The supposition is that fire plays a part, directly or indirectly, in producing the right canopy conditions for the host.

Conservation of this species

Current action

  • Only known site is an ASSI and SAC

  • Other possible sites are being searched on an ad hoc basis.

Proposed objectives/actions

  • Maintain the existing population

  • Conduct full search of the site to determine the size of the population

  • Raise awareness of the species in case it is found elsewhere.

What you can do
Contact the Northern Ireland Fungus Group with any potential record of this species. Some species of fungi can be difficult to identify, but if you are interested, please contact the Northern Ireland Fungus Group for details of how to record fungi. Records can be sent in using online recording forms or by contacting

Further information

Northern Ireland Fungus Group

British Mycological Society Fungal Records (UK wide data)

Ellis, M. and Ellis, P. (1985). Microfungi on Land Plants. Richmond Publishing County Slough.

Hansen, L. and Knudsen, H. (2000). Nordic Macromycetes Vol.1 Nordsvamp. Copenhagen.

Text written by:
David Mitchel

iNaturalist: Species account : iNaturalist World Species Observations database