Botanical Name: Pandanus julianettii
Synonyms: Pandanus jiulianetti Martelli.
Common Names:Karuka, Karunga, Pandanus nut
Habitat: Pandanus julianettii is native to Australasia – New Guinea.
Pandanus julianettii is an evergreen Shrub growing to 4 m (13ft) by 3 m (9ft) at a fast rate.
The tree is dioecious (individual plants either have male flowers or female ones), with male trees uncommon compared to females. It reaches 10–30 metres (33–98 ft) in height, with a grey trunk of 30 centimetres (12 inches) in diameter and supported by buttress roots. The trunk has white mottling and is generally smooth with occasional warts or small knobs as well as rings of leaf scars. Inside the trunk is pithy and lacking cambium. The top of the tree sometimes branches, producing three or four crowns of leaves. Each crown will produce a single cluster of nuts, typically once every other season. Production is affected by the seasonality of local rainfall.
Leaves spiral up the trunk in opposite pairs. The large leathery leaves are 3–4 metres (9.8–13.1 ft) long and 8–12 centimetres (3.1–4.7 in) wide. The apex of the leaf is attenuate and doubly-pleated, with prickles pointing up at the tip and along the margins and midrib. The leaves are dark green on top and dull cyan underneath.
The inflorescence on male trees is a densely-branched spadix with a dozen long spikes, each containing many staminate phalanges. In each phalange is a column 3 mm long topped by up to 9 subsessile anthers. The male flowers are white, and the whole male flowering organ may be up to 2 metres (6 ft 7 in) long.
The pollen has a psilate exine (unornamented outer wall) 0.8 ?m thick. The ornamentation is granular between echinae (short spines). The ulcerate aperture is 3 ?m in diameter. Pollen grains measure an average of 30 × 14.5 ?m in size.
On female trees, the inflorescence is a single ellipsoid or ovoid syncarp, or fruiting head, with off-white bracts. Female flowers can produce fruit without pollination, and are typically the only trees cultivated. The tree stops making leaves when new fruit is growing. The syncarp has up to a thousand densely-packed single-celled carpels that later turn into drupes.
The clavate, pentagonal drupes measure up to 12 cm long and have a sharpened base, but typically are 9×1.5 cm, and are a pale blue-green color. Each cluster contains about 1000 nuts. The endocarp is bony and thin, 5½ cm long, with rounded edges about 1½ cm wide. The seed-bearing locule is around 4 cm long. The core of the mature head (mesocarp) has an appearance like honeycomb and is spongy and pink. The top of the mesocarp is fibrous, from 3 cm long and up. Though Martelli did not have a complete syncarp, he knew the cluster of fruit must be large, estimating at least 30 cm in diameter. He was correct, as the fruiting cluster is typically 15 to 30 cm in diameter. A mature head and stalk weigh up to 16 kg, but average 6 kg.
It most closely resembles P. utilissimus, which is found the Philippines. People also harvest and eat nuts of P. antaresensis, P. brosimos, P. dubius, P. iwen, and P. limbatus, and P. odoratissima.
A plant of the humid tropics, where it is found at elevations from 1,700 – 2,900 metres. Plants grow best in areas where the mean annual temperature is within the range 13 – 24c, but can tolerate 6 – 30c. They may tolerate temperatures as low as 0c for short periods and down to 3c for prolonged periods. They prefer a mean annual rainfall in the range 3,000 – 4,000mm, tolerating 2,500 – 4,000mm. Succeeds in sunny positions and in light shade. Prefers a well-drained, humus-rich, light to medium soil. Prefers a pH in the range 4.5 – 5.5, but tolerates 3.5 – 5.6. Plants can be harvested for their fibre the first time 6 – 8 years from planting, with an economical life of 20-40 years and with a total lifespan of up to 70 years. Require 90-120 days from flowering to fruiting and have no obvious seasonality. This species has potential for commercial use. Branches do not have dormant buds and so will not resprout if cut back into the old wood. A dioecious species, both male and female forms need to be grown if fruits and seed are required.
Seeds are edible. The seeds are oily and contain a fair amount of protein. Sometimes the inner leaves and the tips of the aerial roots are eaten cooked
On New Guinea karuka is cultivated crop, and has been used as a major food source since nearly 31,000 years ago in the Pleistocene. In PNG nearly 2 million people (almost half the rural population) live in regions where karuka is commonly eaten. There is high demand for it in the New Guinea Highlands: Entire households (including pigs, who are sometimes fed the fruits) will move from the valleys to higher elevations at harvest time, often for several weeks. Each household will average 12 to 176 trees.
Medicinal Uses: Not known.
A fibre obtained from the plant is used for making textiles.
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