The trunk of this fern has a black, woody core of bone-like texture covered with matted rootlets which by their increase keep adding to its diameter. According to Hooker the trunks are occasionally 30 to 50 ft high in the wild and as much as 4 ft in diameter. In the wild the fronds of large old trees are up to 12 ft long, tapering to a point at the end; in smaller, younger ones 4 to 6 ft long. They are twice pinnate, the primary divisions up to 18 in. long, thus giving the fronds a diameter of 3 ft. The ultimate divisions are 1 to 2 in. long, 1⁄4 to 3⁄8 in. wide, pinnately lobed, upper surface dark bright green, lower one dull. The life of a frond is from one to two years, and when a new tier of the young, bishop’s crozier-like fronds are uncurling in spring, those of the older tier start to droop downwards and fall against the stem, where they soon die but cling on for several years. There they serve a useful purpose in keeping the youngest rootlets of the trunk moist and growing, and although to many people somewhat unsightly, undoubtedly add to the vigour and rate of growth of the plant.
The dicksonia is a native of New South Wales, Victoria, S. Australia, and Queensland, as well as of Tasmania, where 10 to 20 ft is the usual height.
It thrives and reproduces itself freely at Caerhays Castle, Trewidden and Penjerrick, Cornwall; at Logan in Wigtownshire; and in Eire at Derreen and Rossdohan, Co. Kerry. At Penjerrick the tallest has a stem 141⁄2 ft high and 43⁄4 ft in girth (1966). The colony at Derreen, Lady Mersey tells us, was planted around 1900. The tallest there have less luxuriant fronds than the younger ones and have put on little growth in the past twenty-five years.
A thriving colony of this fern might well serve as an indicator of the British climate in its mildest and dampest form. Apart from freedom from severe frost, shade, moisture and protection from wind are its chief necessities.