Calophyllum Linnaeus is one of the largest genera of Calophyllaceae with about 190 living species. Until now, there have been two pollen records of Calophyllum from the Middle Miocene of Thailand. 

In a recent study published in Palaeoworld, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences reported well-preserved fossil leaves of Calophyllum from the late Oligocene–Early Miocene of the Ban Pu sub-basin in the Li Basin, Lamphun Province, northern Thailand. It is the first macrofossil record of this genus in Thailand. 

The researchers collected five fossil Calophyllum leaves from the Ban Pu sub-basin of Li Basin, Thailand. They identified the fossils by detailed morphological comparison with leaves of extant and fossils. The fossils were assigned to Calophyllum, based on several key leaf characteristics, such as oblanceolate or oblong in shape and parallel secondary veins, nearly perpendicular to the midvein, and secondary veins alternate, closely placed, craspedodromous, parallel, dense, and distinct on the surface, forming marginal veins. 

The leaf fossils from the Li Basin are most similar to C. suraikholaensis. Based on the morphological details, it is difficult to further assign the fossil leaves to the species level with the limited morphological characters preserved. Therefore, the researchers treated these fossils as Calophyllum sp. 

"Our fossils are the first macrofossil record of Calophyllum in Indochina. The fossils in this study, together with previous fossil records, show that, the vast regions from India through the Indochina Peninsula to south China were connected by subtropical forests with floristic exchange in the Miocene. It suggests that India may have been a center of origin for Calophyllum and that it spread to other regions," said SU Tao of XTBG. 

The discovery of Calophyllum fossils represents a humid, subtropical to tropical climate in the late Oligocene–Early Miocene in the Li Basin.

Fossil leaves of Calophyllum suraikholaensis. (Image by XTBG)