New Zealand’s native orchids are extraordinary plants and difficult to spot in the wild. But there are some rare species many might not even recognise as living things.
Cooper’s black orchid is one of them. Classified as nationally critical and as rare as kākāpō, these orchids spend most of the year living underground in the form of a potato-like tuber, sprouting a stick of delicate, unassuming flowers only briefly during the height of summer.
Since Te Papa botany curator Carlos Lehnebach first identified this potato orchid in 2016, fewer than 250 adult plants have been found, limited to three sites across New Zealand. A pine forest in the Wairarapa is the only North Island site with a small remnant population. “There were fewer than 20 flowering plants at the site,” Lehnebach says. “In the past two years, this number has fluctuated between 10 and only two.”
The orchid is found nowhere else in the world. “Considering the amount of deforestation the Wairarapa Plains have been subjected to since people arrived in New Zealand, this orchid could well be the last surviving creature from the time of those pristine forests.”
Now, with other botanists, Lehnebach is using the orchid’s unusual feeding habit to sprout new seedlings in a laboratory at Wellington’s Ōtari Wilton’s Bush, the country’s only botanical garden focused solely on native plants. Like all orchids, Cooper’s black has a close association with underground fungi – the fungus supplies the plant with nutrients and minerals from the soil in return for carbon. But for other orchids, this symbiosis is transient. They rely on this fungal life support mostly during germination.
Orchid seeds are tiny and include no food for the embryo to feed on. They need a fungal partner to feed them until their leaves are formed and they can start making their own food through photosynthesis. However, a group known as Gastrodia, to which the Cooper’s black orchid belongs, never produces the tongue-like fleshy leaves typical of other orchids. They rely on fungi to keep “stealing food from other photosynthetic plants or from decaying plant material”.
This lifestyle is uncommon, says Jennifer Alderton-Moss, a plant conservation researcher at Wellington City Council. “There are eight plant species in New Zealand that use this, and five of them are species of Gastrodia.”
Understanding this symbiotic partner is an essential aspect of conservation, Lehnebach says. The team isolated the fungus from the underground tuber of a common Gastrodia species and then successfully used it to germinate seeds of Cooper’s black orchid. They have now generated almost 2000 seedlings.
“The most exciting development is that, after more than a year, the seedlings have grown from less than half a millimetre to almost three centimetres. They can be handled safely and used for planting in suitable areas in the Wairarapa and to create backup populations at Ōtari.”
About 200 are now large enough to be used in restoration projects and 50 were planted at Ōtari last year. “These numbers are huge, considering only 10 plants were found in the wild last summer.”
For Lehnebach and the team, saving one of our most threatened orchids and reintroducing it into the wild is a botanical dream come true. But the seedlings also support research to understand the biology of other orchids. “We know very little about the fungal preferences of New Zealand orchids, but our research is changing that. Apart from the potato orchids, we have now identified fungal partners of spider orchids, greenhood orchids and some perching orchids. Many of these orchid groups include threatened species, so we are hoping to do the same as we’re doing with Cooper’s black orchid.”
