Large Shrub Epiphytes

As well as being larger than those of the preceding category, these also eventually send a root to the ground and so overcome the water supply and soil nutrient problem.

Puka (Griselinia lucida)⁴⁵ is the most notable in this category. Its large, dark green shining leaves usually contrast so strongly with the foliage of the supporting tree that it stands out even to the casual observer (Fig. 45). Puka is distributed in lowland forests throughout the North and South Islands, but is more common in the north. Its seedlings generally establish in asteliad nests situated at branch forks and its roots ramify through the humic soil. After a few years a strong root begins to grow down the trunk of the supporting tree towards the ground. This root and its branches are closely appressed to the bark of the trunk, and frequently grow into crevices and behind bark flakes. The root tips are white and smooth, but a short distance away from them the root surfaces are often densely clothed with short root hairs. Where the roots are in contact with the trunk, they are anchored by the root hairs and the union is sometimes so complete that when the roots are pulled away they either remove portions of bark or leave strips of their own tissue behind.

Generally, when the root tips reach the ground, one main vertical root enlarges greatly until it attains a diameter of 10 cm or more. This main root usually has a few major branches near the ground and the whole system has a very distinctive appearance resulting from the more or less continuous and pronounced longitudinal grooves and ridges of page 80the bark (Figs. 46, 47). In its upper parts the main root gives rise to slender, horizontal, girdling roots (Fig. 48), which often encircle the trunk of the supporting tree many times and so ensure that the puka will not be dislodged even by the strongest gale.

Two other species, Griselinia littoralis and Pseudopanax colensoi, although mostly terrestrial, can grow as epiphytes in the moist montane or higher latitude forests they favour. When growing as epiphytes they are generally beyond the altitudinal or latitudinal range of asteliad nests and

Figure 46 Distinctively fluted roots of puka (Griselinia lucida) on kohekohes. Waikanae, southern North Island.
Photo: M. D. King.

page 81so establish in the moss and lichen cushions of branch forks. Like the puka, they eventually send one or more roots to the ground.

Broadleaf (Griselinia littoralis) is the only other species of its genus in New Zealand. Its leaves are smaller than those of puka, yellowish green and symmetrical or only slightly asymmetrical at the base. In puka, however, the leaf base is very asymmetrical as the two parts of the leaf divided by the midrib are of quite different lengths. Broadleaf has been observed as an epiphyte on a variety of trees. Its descending roots are

Figure 47 (opposite) Roots of puka (Griselinia lucida) on tawa (Beilschmiedia tawa). The arrow indicates the stem of a white climbing rata (Metrosideros perforata). Paraparaumu, southern North Island.
Photo: M. D. King.

Figure 48 (above) Puka (Griselinia lucida) showing girdling roots. Waikanae, southern North Island.
Photo: M. D. King.

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Figure 49 (above) Mountain five-finger (Pseudopanax colensoi) on a kahikatea. National Park, central North Island.
Photo: J. W. Dawson.

Figure 50 (right) Descending roots and a few girdling roots of the epiphyte northern rata (Metrosideros robusta). Te Marua, near Wellington. Photo: M. D. King.

often more massive than those of puka, but they are not grooved. The species ranges throughout New Zealand including Stewart Island. Beyond New Zealand Griselinia is found only in Chile, where there are five species, at least some of which are epiphytes.

Mountain five-finger (Pseudopanax colensoi) also has a wide range, but is absent north of 36 °S and from Stewart Island. I have observed it growing as an epiphyte on kaikawaka or mountain cedar (Libocedrus bidwillii) on Mt. Taranaki (Egmont) and on kahikatea (Dacrycarpus dacry-dioides) on the volcanic plateau near Mt. Ruapehu (Fig. 49).

The descending roots of puka and mountain five-finger seem too slender in relation to their height to stand alone when the supporting trees die, but this may be possible for the more massive roots of the broadleaf.