Note the large knobbly brown fruit at the bottom of the photo.   Bangkal  Nauclea orientalis is a common small tree of river banks in Borneo.  In December  2016 when we visited the Kinabatangan river, the Bangkal trees  along the bank were flowering  and fruiting, providing a feast for the local wildlife including Proboscis Monkeys, Silvered Langurs, Long-tailed Macaques and fruit bats.

01 Nauclea orientalis 3P7A7584
The  round pop pom flower heads  provide nectar for fruit bats, squirrels, bees and wasps.
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The woody knobbly fruit can grow up to 8 cm diameter but the seeds are less than 1mm long and 0.5mm wide, making them easy to swallow by bats and fish.
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The fruit are edible but are very  woody and taste very bitter to humans. The  fruit are one of several species in Borneo which have evolved a very low sugar content so that the tiny seeds can be swallowed and dispersed by  leaf eating langurs such as the Proboscis monkey.
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Long-tailed Macaque family grooming each other in a  fruiting Bangkal tree. With so much food available close to hand there is plenty of time to play.
Nauclea orientalis distribution map from Wikimedia Commons. It may seem surprising that a fruit so popular with primates  is distributed so widely in Wallacea, New Guinea and Australia where there are so few primates. The explanation is that outside Borneo the main dispersers are giant fruit bats known as Flying Foxes and leaf eating marsupial possums. In Australia N. orientalis is known as the Leichhardt Tree.