Date:  22 July 2021

Corybas carsei, also known as the swamp helmet orchid, is critically endangered and found only at Whangamarino Wetland, an internationally recognised Ramsar wetland site in the Waikato.

Three times a year a team of Department of Conservation (DOC) rangers wade into the 7,000-hectare swamp to monitor the plants. This month they were joined by researchers from Museum of New Zealand Te Papa Tongarewa, and Massey and Victoria universities to find answers to questions about the plant’s mysterious partnerships and reproduction.

Very little is known about the biology of this orchid. Carlos Lehnebach, Botany Curator at Te Papa, says the plants are all found within a single patch. It raises questions about what may be preventing the plant from establishing outside of this site – potentially the absence of the orchid’s specific fungal partner or its pollinator. MSc students, Jennifer Alderton-Moss – also a DOC Scholarship recipient – and Tingyu Qin are working to uncover these closely held secrets.

The relationship between orchids and fungi begins at the seed. Orchids have the smallest seeds in the world, with a single plant producing millions of seeds.

“A typical orchid seed is the size of a speck of dust, making it light enough to be dispersed by the wind over very long distances,” says Waikato Biodiversity Ranger, Kaitlin Morrison.

“Most other seeds contain a package of food which the seedling will use to help it germinate. Orchid seeds, however, do not. Instead, they have a single thin seed coating that forms a balloon around the microscopic embryo, aiding its wind dispersal.”

Fungi make up for the lack of food reserves.

“To germinate, the seed engages in a close relationship with a fungus,” says Kaitlin Morrison. “The fungus is mycorrhizal, which means it lives in the roots of plants. The plant receives nutrients from the soil through the fungus, and the fungus receives carbohydrates from the plant. It’s win-win situation.”

Most orchid species have a special relationship with their own preferred fungal species and will not germinate unless the specific fungus is in the soil. Jennifer Alderton-Moss is researching this relationship.

“We are attempting to isolate the fungal species through Jennifer’s work,” says Carlos Lehnebach. “When we know which fungus the orchid needs, we can germinate seeds in the lab and transplant them into the wetland.”

All the seed germination work is done at Ōtari Native Botanic Garden in Wellington. This is an important piece of the puzzle. It is suspected the fungus might be absent in large parts of the wetland’s soil, possibly explaining why the plant population isn’t expanding.

“When we transplant seedlings into new sites, they’ll bring their fungal partners with them, hopefully colonising the soil so in future more plants can establish naturally,” says Carlos Lehnebach.

“We are also trying to understand the genetic diversity of the plant,” says Carlos Lehnebach. “There is a question about whether the plants are multiple unique individuals, or clones of a single individual. The implications of that answer are significant.” Tingyu Qin’s thesis research is looking into this.

The team are also investigating pollination – how the plant reproduces sexually – and whether it self-pollinates or needs the help of an insect.

The orchid has a single heart-shaped leaf no bigger than a fingernail and is between 10–30 mm tall when flowering. Finding the tiny plants in a relatively giant swamp requires a determined effort.

“We crawl around on the ground where there are known plants, getting splinters from a plant we call The Stabber, also known as Schoenus brevifolius,” says Kaitlin Morrison. “We wear gloves, long sleeves and glasses and take splinter probes with us. Transects are set up at three sites with one-meter-wide lines between 10–16 meters long. We crawl along those lines and when we find a leaf we measure where it is in centimetres. It’s very precise work!”

With only 565 individual plants left, the scenario might seem dire; but there is also a quiet determination to save this mysterious plant, the kind that sends rangers and researchers crawling into a swamp and working hard both in the field and lab to uncover its secrets.  

The orchid's main threats are habitat loss and theft by humans – so the plants’ exact location within the wetland is kept secret.

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