The photo above shows the undersurface of a leaf of Ficus oleifolia growing on Gunung Silam a small mountain on the east coat of Sabah, Malaysian Borneo.
The undersurface of the leaf is covered in small sunken pits (a pattern known as known as “foveolate”) which is a characteristic of several species of root climbers in Sections Rhizocladus and Kissosycea in Borneo. Note also the very prominent regular white dots on the upper surface of the leaf. These white dots are glands known as hydathodes which expel excess minerals from the sap of the plant, a process known as guttation.
The soil on Gunung Silam is very rich in minerals normally toxic to plants, such as nickel and guttation may be a way of removing these minerals from the plant.
Thanks to Mellinda Jenuit and the SFGC team for information and photos.
