Excerpt from Visitor's Guide to Canterbury, 1982 Edition:

"... beside the weathered stones of the ancient Kirkgard lays the oldest graveyard on the islands. Thought to have been in  continuous use since at least the mid 11th to the early 17th century, this hallowed ground has been the resting place for many of the ancient aboriginals to the island. After visiting the impressive headstones and looming mausoleums, note the canopy of broad leaves shades the cemetery. Thick fruits line the twisted and gnarled branches of the trees, ripening on heavy branches. Ratatoskrs are found chittering and skittering, protecting the engorged fruits. Ancient Skraelmen tales tell of the curious actions of these creatures, and how they would carry the messages from the graves below to the Great Cauntantowwit..."

Overview

A common sight across the archipelago from the forests of Nishsystir to the ancient graveyards of Freyfjord, the Idunn Tree (Morus ydun) is an endemic variety of mulberry. Due to the wide array of different environmental conditions found on the Mossfells from mountain highlands to swampy forests, the Idunn tree can vary greatly between islands. The characteristic that is most iconic about the Idunn tree is its large fruit. Sometimes called an Idunn apple, the fruit is generally the size of a pear or apple but can sometimes be as small as cherries or as large as a white pumpkin. 

Like other members of the Morus genus, Idunn trees are fast growing, but require 10 years to achieve maturity. Flowers are small, white, and held on pendulous catkins which grow on both new and old growth. The color of the fruit is generally a purplish red, but can also be pale pink or even green in some varieties. Unlike other relatives in the mulberry family, the fruit of the Idunn tree has a thick skin similar to that of a mandarin peel covering the segmented portions. In some varieties, the peel can be as thick as that of a grapefruit, but in commonly cultivated varieties the peel is so thin it can easily be eaten.

The Idunn tree is thought to have arrived on the Mossfells around 16 million years ago. Descended from mulberry seeds likely carried in the guts of passerine birds blown to the islands, the Idunn tree has now become a key component of the forests of the island chain. As with many of the endemic fauna of the islands, the trees have also experienced several unique ecological stimuli which have influenced their evolution. 

Based on geological evidence, it is hypothesized  that during the middle Miocene forests on the Mossfells were much more humid and much of the island land would be submerged during tides. As a result Idunn trees  have a high resistance to salty conditions and can contribute to the development of mangroves. 

Another adaptation of the Idunn tree to a salty, coastal environment is the fruit peel. Unlike other members of the Morus genus, the Idunn apple is unique for creating a fibrous and water-resistant peel around the fruit and seeds. The peel provides protection to the fruit from salt and the motion of the sea. However, the Idunn tree is not entirely resistant to the ocean, and can still be threatened by high salinity environments. It appears that the Idunn tree is a species caught in between niches: a tree analogous to a mangrove and a tree more similar to the original mulberry.

It appears that with the decrease in global temperatures starting in the Pleistocene, land no longer was scare on the archipelago. This allowed the Idunn tree to take advantage of larger forests and not complete a full transition to a mangrove resident. However, it still retains the fibrous peel of its ancestors, enabling the fruits some protection from the grinding/chewing teeth of the mammals which arrived during the Pleistocene. 

Presently the Idunn tree is seen on nearly every island in the Mossfells with many different morphs according to local environment. Thanks to the long growing season, the Idunn apple is a steady source of food for many animals on the islands - both endemic and introduced. The Idunn apple is a prominent feature in the mythology of the Viardrmen and Skraelmen cultures, often associated with bounty, harvest, and fertility. English accounts of the "magnifesent orchards layn by  nature herself" gave the islands of St. James and St. Anne the moniker the "Bountiful isles". Several cultivars of Idunn apple have been domesticated and are eaten raw or used for pastries and jams. On the Mossfells, the popular soda Vulcan!™  is made with Idunn apple and is known for "a sweet berry taste with a dream of island paradise".