Department of Conservation eager to uncover secrets of rare swamp orchid

The orchid has a single heart-shaped leaf no bigger than a fingernail and is 10-30mm tall when flowering. Photo / Te Papa

Department of Conservation rangers and visiting researchers from Te Papa Museum are going above and beyond to find out how the rare and threatened swamp helmet orchid reproduces.

The swamp helmet orchid (Corybas carsei) is critically endangered and found only at Whangamarino Wetland, an internationally recognised Ramsar wetland site near Te Kauwhata in the Waikato.

Three times a year a team of DoC rangers wades into the 7000ha swamp to monitor the plants. The orchid has a single heart-shaped leaf no bigger than a fingernail, and is 10-30mm tall when flowering. Finding the tiny plants in a relatively giant swamp requires a determined effort.

Last month, the DoC team focused on finding answers to questions about the plant's mysterious partnerships and reproduction.

Waikato biodiversity ranger Kaitlin Morrison says: "We crawl around on the ground where there are known plants, getting splinters from a plant we call The Stabber (Schoenus brevifolius) and take splinter probes with us. Transects are set up at three sites with 1m-wide lines between 10-16m 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 orchid's main threats are habitat loss and theft by humans, so the plants' exact location within the wetland is kept secret.

Little is known about the biology of this orchid. Te Papa botany curator Carlos Lehnebach has been part of the team skimming the swamp, and says the plants are all found within a single patch.

This observation raises questions about what prevents the plant from establishing beyond this site - potentially the absence of the orchid's specific fungal partner or its pollinator.

The swamp helmet orchid (Corybas carsei) is critically endangered and found only at Whangamarino Wetland near Te Kauwhata. Photo / Supplied

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.

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

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

Fungi make up for the lack of food reserves. "To germinate, the seed engages in a close relationship with a fungus. The fungus 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. DoC scholarship recipient Jennifer Alderton-Moss is researching this relationship.

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

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."