The tiny turtle nesting  island of Pulau  Talang Talang Kechil  just off the coast of SW Sarawak is the only proven location in Borneo of Ficus callosa south of the Sabah border. Ficus callosa is locally common in Sabah in coastal areas around Kota Kinabalu and Sandakan  and also  near Kota Belud and Tenom. Satellite photo from Google maps.

Callosa map Berg (2005) - Orange star
Corner’s (2005) F. callosa distribution map copied from Berg & Corner (2005)  shows that Ficus callosa  has a very wide native distribution from Sri Lanka and south India in the west stretching to  Timor in the east. In the middle of the map there is a large area including Johore, Singapore, most of Sumatra and all of Brunei, Sarawak and Kalimantan from which F. callosa is absent.    The 1980 collection of Ficus callosa by Bernard Lee of the the Sarawak Forest Department on Pulau Talang Talang Kechil in SW Sarawak (orange bulls eye) therefore poses a puzzle.
Ficus callosa Pulau Talang Talang Kechil Label-L.1605993.jpg
Ficus callosa collected on Pulau Talang Talang Kechil in SW Sarawak in 1980 by Bernard Lee.
Ficus callosa Talang Talang enhanced1605993 WEB.jpg
Ficus callosa collected on Pulau Talang Talang Kechil in SW Sarawak in 1980 by Bernard Lee.
Callosa Kalimantan TEXT WEB -L.1605994.jpg
Above: A collection of juvenile leaves of F. callosa labelled  “Borneo” deriving from Teijsmann’s 1859-1860 botanical expedition to the Moluccas (Maluku)  in Eastern Indonesia.

Teijsmann did not visit  Borneo on his  1859-1860 Moluccas expedition so the listing of Borneo is likely a location error. The famous Dutch botanist Teijsmann only made one expedition to Borneo from his base at the Bogor Botanic Gardens (Buitenzorg).  This was  in 1874 when he collected herbarium specimens along the Kapuas river and around Sintang and Pontianak in West Kalimantan.

Callosa Kalimantan ORIGINAL WEB-L.1605994 .jpg
Teijisman’s Borneo collection of Ficus callosa. This collection represents the juvenile leaves of Ficus callosa  and was originally identified as an Artocarpus. It was correctly identified by Corner in 1954 in the Leiden herbarium. The location given as Borneo probably relates to Sintang in West Kalimantan  but could be an error.