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Forest Flora – Ryparosa kurrangii

 In Flora, Forest Flora, Learn, News

 

Ryparosa kurrangii © Suzanne Lennox

#ForestFlora -The Remarkable Ryparosa kurrangii: A Living Gem in the World’s Oldest Rainforest

The remarkable Ryparosa kurrangii tree, a true rarity, calls just a small corner of the Daintree rainforest home. Named after “kurrangi,” the local Eastern Kuku Yalanji word for ‘Cassowary’ due to the role they play in the species germination, this tree currently has no universally accepted common name, though it is sometimes called the “Daintree Ryparosa” or the “Australian Ryparosa.” Known for its rarity and limited range, this tree only grows in the tropical lowland rainforests between the Daintree River and Cape Tribulation, a place of deep cultural and spiritual significance for the Eastern Kuku Yalanji People, traditional custodians and knowledge holders of Eastern Kuku Yalanji Country for over 50,000 years.

The Daintree is the oldest continuously surviving tropical rainforest on Earth, with a history spanning 180 million years. In this ancient ecosystem, the Ryparosa kurrangii has evolved alongside countless other plant and animal species. This environment supports extraordinary biodiversity and intricate interconnections that make species like Ryparosa kurrangii so unique and dependent on their surroundings.

What the Cauliflory?

The Ryparosa kurrangii is a small to medium-sized tree, typically growing to about 15-20 metres, under the rainforest canopy. One of its most fascinating features is cauliflory—a characteristic where flowers and fruits grow directly from the trunk and main branches. This adaptation allows rainforest animals easier access to the tree’s flowers and fruits, which grow in clusters on the lower trunk and emit a strong, sweet fragrance.

The tree’s leaves are dark green, glossy, and leathery, with a distinctive lance-shaped outline and smooth edges. Its small yellow-green flowers bloom from June to September, followed by fruits that mature from October to December. These drupes, or fleshy fruits, are covered in dark hairs and turn from dark green to yellow-orange as they ripen. Cauliflory, common in tropical rainforests but rare elsewhere, gives pollinators like insects and frugivores, including cassowaries, easy access to the tree’s flowers and fruits, enhancing their role in the tree’s lifecycle.

Symbiosis in Action: Ryparosa kurrangii and its Rainforest Partners

The Ryparosa kurrangii depends heavily on the Southern Cassowary, a large, flightless bird native to northern Australia’s rainforests, for its survival. When cassowaries eat the tree’s fruit, the seeds pass through their digestive system, which significantly boosts their germination rate from a mere 4% to an impressive 92%. This unique gut-passage process not only enhances seed viability but also reduces fruit fly infestation—a common threat to the seeds. Incredibly, scientists have been unable to replicate this effect through artificial means, highlighting the special relationship between this rare tree and the cassowary.

The tree also forms a fascinating partnership with certain native ant species. Ryparosa kurrangii produces small food rewards from its leaves and branches, attracting ants that protect the tree from leaf-eating insects and clear moss from the leaves. This reduces competition for sunlight in the shaded rainforest, an essential factor for this slow-growing tree.

Ryparosa kurrangii © Kai Squires

Conservation Challenges and the Need for Rainforest Protection

The Ryparosa kurrangii is currently listed as “near threatened” under The Nature Conservation Act 1992 (NCA), reflecting its vulnerability within a restricted area of tropical rainforest. This tree’s survival is tied closely to the unique conditions of its native environment, and the fact that attempts to propagate it outside the Daintree have proven largely unsuccessful underscores the need to protect and expand its natural habitat through conservation and rainforest regeneration efforts. By preserving and restoring these regional rainforests, Rainforest Rescue is not only supporting Ryparosa kurrangii but also the larger web of life in this delicate ecosystem.

The Ryparosa kurrangii is a remarkable reminder of the complexity and beauty of Australia’s rainforest ecosystems, and its survival depends on the delicate and complex relationships it shares with the plants, animals, and people of the Daintree.

Fun Facts about Ryparosa kurrangii

  • Cyanide in the Leaves – R. kurrangii’s Deadly Defense Strategy: Recent studies have identified R. kurrangii as a model plant in which to investigate plant-herbivore interactions and plant defensive chemicals (Webber 1999).  The species is known to liberate volatile hydrogen cyanide (HCN) upon tissue disruption in a process known as cyanogenesis. Because cyanide is a respiratory toxin, its presence in plants has been shown to act as a trait conferring resistance against generalist herbivores (e.g. Gleadow and Woodrow 2002; Hruska 1988).  Importantly, leaves from some plants contain levels of cyanide that are amongst the highest ever reported while individuals within populations seem to vary greatly in their (genetically based) capacity for cyanogenesis (Webber 1999).
  • Honouring Place and People: The tree’s name, kurrangii, is derived from the Eastern Kuku Yalanji word for Cape Tribulation and is also similar to “kuranji,” the Eastern Kuku Yalanji word for “cassowary.”
  • Nature’s Perfect Partnership: Ryparosa kurrangii relies on cassowaries to germinate its seeds, a process scientists have been unable to replicate in the lab.
  • Easy Pickings: This rare tree grows flowers and fruits directly on its trunk, making it easier for animals to access them in the dense rainforest.
  • Ant Allies: The Ryparosa kurrangii has specialised relationships with ants, which help keep its leaves clean and protect it from insect herbivores.

References

This article was written for Rainforest Rescue by Sian Bostrom – for more of Sian’s work, visit http://www.sianbostrom.com/

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