Photo above shows  two different species of root climbing fig plants  Ficus recurva (left) and Ficus villosa (right)  growing next to each other  on an old  stump next to the  Temburong river, Brunei. Both plants show  bathyphyll  (juvenile) phase leaves.

There are two groups of root climbing figs in Borneo. Section RHIZOCLADUS (11 species) and Section KALLOSYCE  (11 species). All root climbing figs  grow from the ground upwards  tightly clinging to a tree trunk. When they reach the canopy their leaves change shape and they start branching and fruiting.

During the root climbing  (juvenile) phase the leaves are known as BATHYPHYLLS and when they reach the canopy, change shape and start fruiting  the (adult) leaves are known as ACROPHYLLS.

In this article we illustrate both the bathyphyll  (juvenile) and acrophyll (adult) leaves of Borneo’s 2 most common root climbing figs, F. recurva and F. villosa.  This enables them to be easily distinguished in the field in their bathyphyll phase when they are not fruiting.

Ficus recurva:  Bathyphyll (juvenile)  leaves. Note the roots growing on the opposite side of the leaves. These roots are are used for climbing up tree trunks (root climbing).
Ficus recurva : Acrophyll (upper) leaves  when branching and fruiting. Note that there are only 3 to 4 side veins on the leaf. This is an important distinguishing feature from Ficus villosa which normally has 6 to 8 pairs of side veins in the  acrophyll phase .
Ficus villosa: Bathyphyll (juvenile) leaves  growing on rock. The bathyphyll leaves are very distinctive. They are never opposite each other on the liana. The side veins are heavily impressed (sunken) on the upper surface  creating a  corrugated or bullate appearance and all parts of the plant are covered in hairs. Note that there are only four pairs of side veins.
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Ficus villosa: Bathyphyll (juvenile) leaves  growing on a tree trunk. This is a VERY common sight in the forests of Borneo. Many botanists do not realize that F. villosa is probably Borneo’s most common fig as they fail to connect  the very distinctive bathyphyll leaves with the acrophyll (adult) leaves  in most herbarium collections.
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Ficus villosa: Acrophyll (upper) leaves produced in the adult fruiting phase. Note that the number of side veins has increased from 4 to 7 compared with the bathyphyll phase.
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Ficus villosa: Acrophyll (upper) leaves produced in the adult fruiting phase. Note that although the twigs remain very hairy the upper surface of the leaf is much less hairy than the bathyphyll phase.

Most of the root climbing figs in Section Kalosyce and Section Rhizocladus  found in Borneo show differences in their adult and juvenile leaves. See this article on Ficus pumila as an example.