I had discussed the Family Dipterocarpaceae in an earlier post. This is a group of plants coming under the Order Malvales (which includes the likes of Balsa, Baobab, Cacao, Cotton, Durian, Hibiscus, Kapok, Kola, and Okra). The Dipterocarpaceae are named after the type genus Dipterocarpus, having around 70 species in the tropical forests of South and Southeast Asia. Their name is derived from the Greek ‘di’ (meaning two), ‘pteron’ (meaning wing) and ‘karpos’ (meaning fruit). Taken together, they stand for ‘two-winged fruits’, a hallmark of the genus. The wings around the fruits (or seeds) become dry and stiff, helping disperse them over several hundred meters. Apart from Dipterocarpus, the Family includes the following genera:
- Anisoptera (South and Southeast Asia, and New Guinea)
- Cotylelobium (South and Southeast Asia)
- Dryobalanops (Southeast Asia)
- Hopea (South and Southeast Asia, and New Guinea)
- Marquesia (Southern Africa)
- Monotes (Central and Southern Africa, and Madagascar)
- Neobalanocarpus (Malay Peninsula)
- Parashorea (Southeast Asia)
- Pseudomonotes (northwestern Amazon Basin)
- Shorea (South and Southeast Asia)
- Stemonoporus (Sri Lanka)
- Upuna (Borneo)
- Vateria (South Asia)
- Vateriopsis (Seychelles)
- Vatica (South and Southeast Asia)
Their distribution reveals the ancient links between distant southern landmasses – South America, Africa, Madagascar, Seychelles, and South Asia. Though the greatest diversity of Dipterocarps is to be found in Southeast Asia (to be precise, the island of Borneo or Kalimantan), their origins lie in the southern supercontinent of Gondwanaland (which comprised South America, Africa, Arabia, Madagascar, South Asia, Australia and Antarctica). It was in Gondwanaland that the Family Dipterocarpaceae evolved. The supercontinent began to break apart some 180 million years ago, dividing into Western Gondwana (South America, Africa and Arabia) and Eastern Gondwana (Madagascar, South Asia, Australia and Antarctica).
Madagascar and India (i.e. South Asia) formed one land mass lying in the northwestern sector of Eastern Gondwana. They split off from Eastern Gondwana around 130 million years ago and began drifting north, towards Asia. It was here, on this island landmass, that ancient Dipterocarp species flourished. However, further tectonic activity split Madagascar from India some 90 million years ago. While the latter kept moving northwards, the former became an island surrounded by the Indian Ocean. Between 55 and 35 million years ago, India (in the form of the Indian Plate) smashed into the Asia (lying on the Eurasian Plate). It was this gigantic collision that gave birth to the Tibetan Plateau and the Himalayas. That is also how the ancestors of the Dipterocarps reached Southeast Asia. There are two major lines of evidence to trace this journey:
- Botanical: Genetic studies have proved that the closest relatives of the Family Dipterocarpaceae are members of the Family Sarcolaenaceae. This is a group of some 80 species of plants endemic to Madagascar. These evergreen shrubs and trees have several traits in common with the the Dipterocarps.
- Paleontological: Amber (known as Cambay Amber) collected from a coal mine in the western Indian state of Gujarat yielded evidence of tree resin associated with species of the Family Dipterocarpaceae. Dating back to 52 million years ago, the amber showed that Eocene India was covered by Dipterocarp forests.
According to Richard Corlett and Richard Primack, in ‘Dipterocarps: Trees that Dominate the Asian Rainforest’, the ancestral members established themselves on the Eurasian continent some 45 million years ago. This was when a moist corridor was created between South and Southeast Asia. Soon, they underwent a massive evolutionary radiation, proliferating across the Malay Peninsula, Sumatra, Java, Borneo and the Philippines. A secondary centre of Dipterocarp radiation was the island nation of Sri Lanka. Over Southeast Asia, they have given rise to some of the most impressive tropical forests of the world, with individual trees rising as high as 80 m, dominating the canopy and forming the backbone of the ecosystem.
Image Attribution: The image above, sourced from Wikimedia Commons, shows a tectonic plate reconstruction of the globe around 100 million years ago. India (with Sri Lanka near its southern tip) and Madagascar lie next to one another in the Southern Hemisphere, between Africa (to the west), Antarctica (to the south) and Australia (to the east). Arabia is attached to Africa, and a huge ocean separates Eurasia and India. It was around this point of time that the ancestral Asian Dipterocarps evolved on the island continent of India. When India collided with Eurasia, between 55-35 million years ago, they obtained a bridgehead in the Northern Hemisphere. Soon, during the Eocene, they spread all over Southeast Asia, crossed the Wallace Line and reached New Guinea. The image was sourced from the PhD thesis of Pierre Dèzes (1999; Institut de Mineralogie et Petrographie, Université de Lausanne), and uploaded by Moumine.
- ‘Dipterocarps: Trees that Dominate the Asian Rainforest’ (by Richard Corlett and Richard Primack)
- ‘Dipterocarp Biology, Ecology, and Conservation’ (by Jaboury Ghazoul)
- ‘First Family Tree for Tropical Forests’, (dated February 7, 2018, by Aathira Perinchery), The Hindu
- ‘Mapping the First Family Tree for Tropical Forests’ (dated February 5, 2018, originally written by Sarah Nightingale), Science Daily
- ‘Prehistoric Creatures Discovered in Huge Indian Amber Haul’ (dated October 25, 2010, by Ian Sample), The Guardian
- Lowland Dipterocarp Forests (WWF)
- Dipterocarp Trees (Rainforest Journal)