Llanelli Naturalists Newsletter - October 2001 - No 67
Nigel Stringer And Dic Davies

Since 1995 the authors have been recording the distribution of rust species in Carmarthenshire.  Rusts are plant parasites which occur on native plants but are most commonly thought of in relation to the problems associated with commercial crops such as cereals and conifers.  Severe rust infections of cereals can result in total crop failure and there have been many famines over time as a result of this disease.

Although there are considered to be about 6000 species of rust worldwide, only about 300 have been recorded in Britain.  Rusts are microscopic fungi that can only exist on living plants.  Their life cycle is very complex and it is these spore structures that we see on infected plant material.  Spore masses tend to be orange in colour which is why the leaves have a ‘rusty’ appearance – hence the name. Due to the complex nature of the life cycle some rusts have 5 different spore types whilst others have only 2.  To complicate matters even more, these spore stages can be produced on 2 different plant hosts!

The recording of rusts in Carmarthenshire started in 1995 and up to this date there were only a handful of records for the county.  Rust species are generally under-recorded in the whole of Britain and for Wales only about 500 records were listed prior to 1995.  Rusts like other ‘mushrooms’ are seasonal but are dependant on the appearance of a host plant.  Thus, rusts can be found on a particular plant at all times of year and keen rustologists don’t have to wait for spring and autumn like many other mycologists!

Over the last 6 years the project has grown from a Carmarthenshire base to a whole Wales approach.  This was due to colleagues working in other parts of Wales sending in records and specimens and also the need for a Wales Rust Flora database, which is urgently required in relation to concerns relating to our biodiversity remit.

Thus to date we have over 4500 records for Wales (some dating from the 1850’s) and the Carmarthenshire total now stands at 2000.  The total number of rust species for Wales is 190 (145 found in Carmarthenshire).  The work has proved to be very important in national terms with 34 new plant hosts being found since the last census list in 1966.  These new hosts include species such as Sneezewort (Achillea ptarmica), Hay-scented Buckler-fern (Dryopteris aemula), Black Poplar (Populus nigra ssp.betulifolia) and Reflexed Saltmarsh-grass (Puccinellia distans), all found in Carmarthenshire.  Of great interest is finding a rust new to Britain – Puccinia scorzonericola on Viper’s-grass (Scorzonera humilis) from Glamorganshire. 

The most commonly occurring rust genera have been found on fern species (which constitutes about 5% of the total records).  Literature prior to 1996 indicated that rusts on fern species were ‘very scarce’ or ‘rare’.  Clearly there is a case of under-recording for rusts in general and the need for extra information relating to their distribution and abundance.  One reason for under-recording is the need for microscopic examination of the material to determine certain species of rust, which can infect different host plants.  A case in point are the many rusts found on sedges and grasses.  However, many rusts are host-specific – for example Uromyces muscari only infects Bluebell and Puccinia buxi only Box (Buxus spp).

We do not know the distribution of common rusts on common hosts and members of the Llanelli Naturalists can play their part in the recording scheme.  Of great importance is the correct identification of the host plant (because of host specificity of some rust fungi).  Being a ‘competent’ taxonomist need not put people off, however, as even ‘easily identified’ host plant information is much needed.  There are workers in the rest of Wales who concentrate on single species (Box, Bluebell, polypody fern etc) and this would be a useful contribution by those people who are not confident in identifying complex species groups.

Specimens can be collected (a leaf is all that is required) and pressed as a herbarium specimen.  Details required are: collector, grid reference, date and correct name of specimen.  The specimen should be sent for determination to R N Stringer, c/o Countryside Council for Wales, Beechwood Offices, Talley Road, Llandeilo, SA19 7HR.