Calicium diploellum New to England!

Recent Finds

The most exciting find, however, was a very unexpected species. On the 24 March 2016 I had a casual lunch time dog walk in Great Stubby Hat (SU3011), in the Busketts Wood complex, looking at a few trees of interest on the way. Stopping at one attractive looking old Holly, I noticed a green specked thallus with some possible tiny stalked apothecia on lignum in a Holly lenticel. This looked very reminiscent of Calicium diploellum, a very rare species in Britain and Ireland, but one which I had seen a lot of recently during surveying in Co. Kerry, Ireland. As this had only been found in a few places in Ireland and one in western Scotland, however, this seemed very unlikely (distribution map, NB lacks some recent Irish records), but I collected a little just incase.

The Holly

I did not think much more about it and only just remembered to look at the specimen before going to bed. Under the binocular microscope it looked even more familiar, definitely stalked apothecia with a green speckled thallus. I extracted a couple of smaller apothecia, so as to leave a voucher specimen, just in case, and placed them under the microscope; it looked even more like Calicium diploellum. A quick squash and wow the spores! Brown one septate spores with spiral thickening and 7 – 9 x 4μm, **@!!! it was Calicium diploellum.

Under the microscope

At Little Stubby Hat the Calicium diploellum was confined to exposed lignum in lenticels where the adjacent bark was dominated by Mycoporum lacteum along with some Stenocybe septata. Nearby on the Holly were Schismatomma niveum, Mycoporum antecellens, Mycoblastus caesius and Thelotrema lepadinum. This is the typical habitat of Calicium diploellum in Ireland; the species is invariably found in lenticels, or damaged bark, where the non-lichenised fungus Mycoporum lacteum dominates. The reason seems to be quite simple; Mycoporum lacteum appears to be a bark chloroplast parasite; a fungus that lives like a lichen, but rather than developing a mutualistic relationship with an algae, it simply parasitises the chloroplasts in the bark of the Holly. For this reason Mycoporum lacteum avoids overgrowing the chloroplast free exposed lignum in the leticells. This leaves the lignum habitat free for Calicium diploellum. The main competitor for dry Holly bark is the fully lichenised Lecanactis abietina. This happily overgrows exposed Holy lignum, leaving no habitat for Calicium diploellum. The Mycoporum lacteum, however, does appear to be strongly competitive with Lecanactis abietina to the advantage of Calicium diploellum.

Finding Calicium diploellum in the New Forest was a surprise; the species is otherwise confined to old Holly in hyper-oceanic climates (see updated map below). However, it is very difficult to spot, even when well developed, so can be expected to be under recorded. The species is also restricted by the survival of old Hollies in the landscape, and the occurrence of strong populations of old Holly may be a more significant limitation to its distribution than climate. In Britain, these are only frequent in the New Forest, but are more frequent in Ireland. In Scotland, and even more so Wales, old Hollies are now very rare and restricted to relic trees, mainly on difficult to access cliffs. There is evidence to suggest this recent feature caused by some combination of increased coppicing, sheep grazing and the little ice age, and that old Hollies were a much wider feature of upland western medieval pasture woodland. The distribution of the old Holly habitat suitable for oceanic lichens is best represented by the distribution of Mycoporum lacteum. This is nearly always found on Holly, although it can rarely occur on Birch, Oak and Beech in areas with large populations of Mycoporum lacteum on Holly.