Record numbers of rare Whangamarino orchid allows new research

By Jocelyn Henderson, Ranger (Christchurch)

Controlled burning success means numbers of the nationally critical swamp helmet orchid (Corybas carsei) are well above the target to start research… 🌱

The orchid has a single heart-shaped leaf no bigger than a fingernail, so it’s difficult to find. It’s also extremely rare, known only to exist in a single population across an area of about 275m² at Whangamarino Wetland in the Waikato. We could only find 121 of the tiny plants in 2018.

Habitat modification is the main threat to Corybas (along with orchid thieves), so our team has been carrying out regular controlled burning of the swamp. The “cool” winter burning is carried out on a five-year cycle, burning the scrub which outcompetes the tiny Corybas for sunlight without damaging the underlying peat layer.

This burning of the swamp seems to have turned the tide for the little orchids. In 2020, the team counted an amazing 501 – including 107 outside the monitoring plots! They also found one leaf in a plot that had been empty for seven years, showing the plant is on the move.

However, while we know that fire stimulates flower production – with an increase from 1% to 30% flowering two years after a burn – we don’t know why. Some of the hypotheses are that growth is encouraged by the disturbance and boost of nutrients from the ash, or by increased soil temperatures from exposed ground, or that smoke or ethylene gas stimulates flowering or fruiting.

That’s not the only unknown with this enigmatic little plant. We don’t know much about how they sexually reproduce or what pollinates them, though we suspect that a fly or gnat might be the mystery visitor.

Now that numbers are high enough, we can start doing more research on the plants. We’re collaborating with researchers from Te Papa and two Master’s degree students from Victoria and Massey universities to better understand pollination and the mycorrhizal associates (soil fungi) of this species. Orchids have dust-like seeds which have no energy reserves, so they rely on fungal roots that supply nutrients to the seed for germination and seedling establishment. Understanding more about how they reproduce will help us protect the plant and keep numbers growing.

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Corybas carsei is just one of the precious species at Whangamarino, which is internationally recognised as a Ramsar site for its outstanding biodiversity. It is one of three vital wetlands included in Arawai Kākāriki – our wetland restoration programme. Protecting and enhancing the threatened species at Whangamarino is one of the programme’s key objectives.