Wild service - Alisier - and its rust fungus
The leaves of the Wild Service tree look somewhat like a maple, but its fruits are similar to extremely small apples, often not much bigger than a large pea. The fruits, as a French book states 'fournissent une liquer alcoolique estimée' . The fruits become spotted or chequered as they ripen, and are sometimes called 'chequers'. From this fact, so some books say, may arise the reason for the common name of 'The Chequers' for pubs in Kent, this beer perhaps being an original brew in those parts.
In England, because of the destruction of so many ancient woods, the tree is now uncommon and it is regarded by ecologists as a useful indicator species of ancient woodland. Here in southern France it grows commonly on the limestone soils. The leaves tend to attract your attention because of the orange spots which frequently decorate them. If you look through a lens at one on the underside of the leaf, it can appear as in my photograph. The actual size of this rather beautiful structure is about 5 mm. Out of the orange spot grow a number of small stiff but curved hollow horns. The structure is a fungus and spores are scattered through the horns. The trees in England rarely have this affliction and I have no doubt that, strange though it may seem, this is because of the lack of juniper trees nearby. Juniper trees are even more rare than wild service and wild service and juniper trees growing together rarer still.
The spores fall on stems of juniper in summer and then infect that species of tree. The infected stem becomes swollen and cankered. This can take a few years. In the spring small orange-yellow 'tongues' develop on the juniper stems. These are a secondary form of the rust fungus. These projections produce a different form of spores and they in turn reinfect the young leaves of wild service trees, or a close relative like the true service tree. You cannot find the rust on the wild service unless juniper is growing nearby. In my wood the two species actually touch.