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The karuka (''Pandanus julianettii'', also called karuka nut and ''Pandanus'' nut) is a species of tree in the family Pandanaceae and an important regional food crop in New Guinea. The nuts are more nutritious than coconuts, and are so popular that villagers in the highlands will move their entire households closer to trees for the harvest season.

Names

The specific epithet "''julianettii''" honors naturalist Amedeo Giulianetti, who found the original type specimens.

is a loanword from Tok Pisin. Sometimes the tree is called '' or 'karuka nut pandanus'. The term 'karuka' can apply to both ''Pandanus julianettii'' and '' P. brosimos'', though the latter is usually called 'wild karuka'. Both species, as well as '' P. dubius'', can be called 'pandanus nut'. In addition to ''P. brosimos'', 'wild karuka' can also refer to '' P. antaresensis'', '' P. iwen'', and '' P. limbatus'', but nuts from these trees are a much smaller part of the local diet. In contexts where multiple karuka species are discussed, ''P. julianettii'' is sometimes termed 'planted karuka'. ''P. julianettii'', ''P. iwen'', and ''P. brosimos'' are also in the subsection named ''Karuka'', which is in the monotypic section also named ''Karuka''.

In New Guinea it goes by different names among each of the Papuan peoples. In the Ankave language it is . It is in the Baruya language. The Huli language word is , and it is also in the Duna language. In Kewa language it is ''aga'', but it is unclear which dialect(s). In the Kewa pandanus language it is ''rumala agaa''. The Kalam language term, in both standard and pandanus languages, is , but it can also be called or . The plant is called in the Wiru language. In the Pole language it's called ''maisene''. It goes by ''ank'' in Angal language, and in the Wola dialect. The Imbongu language word is .

The plant also has many names on the other half of the island. In Indonesian it is called ( lit.) and (), but the latter can also refer to ''P. brosimos'' and ''P. iwen''. The Dani people call it ''tuke''. The Lani people call it , but this might be a separate species in the complex.

Description

The species was originally described by Ugolino Martelli from only a few drupes in the collections of the Royal Botanic Gardens, Kew He was hesitant to describe it as a new species from only that, but the characteristics were so salient he published his description.

The tree is dioecious (individual plants either have male flowers or female ones), with male trees uncommon compared to females. It reaches in height, with a grey trunk of 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 long and 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 long.

The pollen has a psilate