Alder Tongue, Taphrina alni. Upton Fen, August 2020.

At this time of year we go looking for Alder Tongue fungi, Taphrina alni. We usually find some on the Alder trees by the River Wensum at Sweetbriar Marshes in Norwich, not far from where we find Alder Goblets in the late winter.

So last Sunday afternoon we went to have a look. We saw several, on the lower branches of Common Alder trees beside the tarred path that runs between the Mile Cross and Sweetbriar Road bridges.

Alder Tongues are a type of plant gall. The Ascomycete fungus Taphrina alni infects an Alder tree and produces chemicals that alter the growth of the woody female catkins (pseudocones), producing the distinctive tongue-like growth, which can grow to at least twice the length of the catkin. The structure is sometimes known as a “languet” (something that resembles a tongue).

The “tongue” tissue derives mainly from the ovarian tissues of the alder catkin or from its bracteoles. (Apparently those curling down usually come from the bracteoles tissues and those projecting upwards usually come from ovarian tissues.) Alder Tongues are smooth-edged and grooved and usually curved.

The fungus produces sexual spores from its asci, which are embedded in the gall tissue, and these are carried by the wind to infect other trees. Often a single female catkin has several Alder Tongues growing from it but sometimes the gall doesn’t develop properly – the Plant Parasites of Europe website has photographs of a gall that has failed to grow.

Alder Tongues can be green, cream, red, purple or brown. Specimens produced early in the season (July or early August) tend to be green, whereas later specimens (mid August onwards) are usually more richly coloured. Old Alder Tongues are brown and the dried structure persists into winter on the mature, browny black pseudocones. They may still be attached to fallen pseudocones in late winter.

Young, fresh Alder Tongue, Taphrina alni. Sweetbriar Marshes, Norwich, last week.

Older, brown, Alder Tongues, Taphrina alni. Sweetbriar Marshes, Norwich, last week.

Taphrina alni has been recorded from many parts of the British Isles, though mainly north of a line from the Thames and Severn estuaries. It has been found as far north as Orkney. (The NBN Atlas had 654 records at the time of writing.) It appears to be becoming more common, with an increase in sightings since the 1990s.

Outside the British Isles, Taphrina alni occurs in several European countries, including Germany, Switzerland, Norway and Denmark. It is has also been found in the USA and Canada.

Other species of Taphrina also cause gall formation in their hosts.

Taphrina betulina causes a gall known as a Witches’ Broom, a dense twig-like formation in the branches of a birch tree. It is the size and shape of a squirrel’s drey and is most obvious in winter, once birch trees have lost their leaves. (But beware: similar growths can also be caused by several other organisms, including other fungi, insects, mites, nematodes and viruses.)

Pocket Plums are caused by Taphrina pruni. The fungus infects Blackthorn (Prunus spinosa) and other species of Prunus, included domesticate varieties of Plum. Infected fruit develop into elongated green structures that resemble small runner beans. affected fruit have no stone.

There are some good photographs of Alder Tongues on the NatureSpot, Living Levels and Botany In Scotland websites.