In the Spring of 2006 my field work was ended abruptly one day by very heavy rain. I decided to look at some indoor plants and went to the Exotic Plant Company at Aldeburgh. In one of their poly tunnels are some large tree ferns (Dicksonia antarctica) and at the base of the trunk of two of these I found patches of a moss. It looked unfamiliar and turned out to be a southern hemisphere species Leptotheca gaudichaudii. The manager of the plant centre was surprised that I had found anything of this nature on the tree ferns because he said that they underwent such a thorough cleansing before import that he had heard of plants being killed during the process. A short time later I went to another garden centre, at Coggeshall, that specialises in similar plants and found Leptotheca gaudichaudii on some of their tree ferns, again Dicksonia antarctica. At this centre there was a bundle of recently delivered tree fern trunks that were completely clean with no sign of any moss.

When browsing round a garden centre in north Suffolk May 2008 I came across a display of tree ferns. These were a mixture of Dicksonia fibrosa and D. squarrosa and were about 50cm. tall. All had some mosses and liverworts growing on their trunks. Some were familiar things that are common in Suffolk such as the mosses Eurhynchium praelongum and Leptobryum pyriforme and liverworts Lophocolea bidentata and Marchantia polymorpha. There were also others that were unfamiliar and in all I was able to identify three mosses Archophyllum dentatum, Leptotheca gaudichaudii and Wijkia extenuata and four liverworts Chiloscyphus coalitus, Lejeuna primordialis, Lophocolea muricata and Teleranea longii. These are all southern hemisphere species and are fairly common in New Zealand. The tree ferns had been imported from Holland and bore the trade name Ponga. I think they must have been imported ready potted and with the bryophytes already well developed. Perhaps there are fewer restrictions on importing tree ferns via Holland rather than direct from New Zealand or Tasmania.

Introduced bryophytes occur in glasshouses in a number of botanical gardens. The moss Leptotheca gaudichaudii has been found growing on the trunk of tree ferns in a garden in Ireland and Archophyllum dentatum amongst filmy-ferns in a damp grotto in a private garden in Cornwall. Also present at this site is an Australian species of filmy-fern Trichomanes venosum, which is thought to have been introduced with tree ferns in the last century.

With the current popularity of tree ferns I began to wonder if any of the bryophytes that I had been seeing in garden centres would survive after being planted in gardens locally. The answer came sooner than expected when I visited the gardens at East Bergholt Place. In a damp area close to a small lake are some fairly large specimens of Dicksonia antarctica and on the base of two of them I found the mosses Archophyllum dentatum and Leptotheca gaudichaudii and the liverwort Lophocolea muricata. Mr Rupert Eley the owner of the garden tells me the tree ferns were planted between four and five years ago, so it is possible for these introduced species to survive given the right conditions. At East Bergholt the tree ferns are planted in an area that remains damp throughout the year, tree cover provides protection in summer and in February the fronds of the tree ferns die and hinge downwards adding further shelter round the base of their trunks.

Bryophytes are unlikely to be the only things imported with tree ferns, so what other strange things are out there waiting to be found?

References

Rumsey, F. J. Archophyllum dentatum (Hook. f. & Wils.)
Vitt & Crosby. Naturalised in Britain. J. Bryol. 23, 341-4 2001.
Smith, A. J. E. The Moss Flora of Britain and Ireland. 2004. CUP.