Many of New Zealand’s native orchids need our help to secure their long-term survival, but it is hard to help when we know so little about them. Master’s student Rebecca Greenwood (recipient of Te Papa Foundation Orchid Conservation Scholarship) is embarking on research to explore the pollinators and fungal-root interactions of a small group of spider orchids from south Auckland.
There are around 120 native orchid species in New Zealand which vary hugely in their flower shapes and colours as well as the kinds of habitats they grow in. Many of these species are rare, poorly understood, and threatened by habitat destruction and fragmentation, meaning that research and conservation efforts are necessary to make sure that these unique plants are still around to appreciate in the future.
Towards this end, several studies have focused on their propagation and fungal partners. Most recently, to avoid damaging orchids growing along the tracks of regional parks around Wellington, an app has been created which indicates the best time for track maintenance works to happen (i.e. when orchids are dormant).
Uncovering the ecology of Corybas “Pollok”
Corybas “Pollok” is a formally undescribed orchid found only on a couple of mossy sandstone cliffs in the Pollok region of Āwhitu Peninsula, south Auckland. With its small, rounded leaves and unobtrusive pale green and maroon flowers, it looks very different to the houseplant orchids people are probably more familiar with.
It has a population of around 750 individuals spread across two neighbouring sites, and this small population size and limited range put it at risk of habitat destruction caused by storms and erosion. In fact, some of the vegetation and habitat in the gully where Corybas “Pollok” is found has already been damaged by storms and flooding over the last couple of years, although thankfully the little orchid has weathered through.
To increase its chances of survival we need to develop a better understanding of this plant’s reproductive biology and ecological requirements. This is what I am aiming to investigate as part of my master’s research.
All about spider orchids
Spider orchids belong to the genus Corybas, which is one of the largest orchid genera in New Zealand. There are currently 21 recognised Corybas species in New Zealand, seven of which are ranked as Threatened or At Risk in the New Zealand Threat Classification System.
Orchids in this genus are found all across the country from Cape Reinga to Rakiura, as well as on the Three Kings Islands, Chatham Islands, and Auckland Islands. Worldwide, there are around 135 species of Corybas and these are distributed from the Himalayas to southern China, the Malay Archipelago, Polynesia, New Guinea, and Australia.
Overseas these orchids are commonly known as helmet orchids. In New Zealand, they earned the name spider orchid thanks to the elongated lateral sepals and petals of many species’ flowers, which give them a spider-like appearance. The plants consist of one underground tuber, one leaf and, when flowering, they form one scentless flower only.
There are other Corybas species in Āwhitu in addition to Corybas “Pollok”, including C. macranthus and two formally undescribed Corybas (C. “pygmy” and C. “tridodd”) which have different ranges and habitat preferences. Comparing the ecology of C. “Pollok” to these other orchids can help with understanding the factors that influence their distribution, possibly uncovering why C. “Pollok” is so uncommon.
Pollination trials: how are seeds produced?
Some plants have flowers containing both male and female structures, which means their flowers can fertilise themselves, either automatically or with the assistance of pollinators, wind or rain. These plants are self-compatible. This feature can be useful in plants forming small populations, but it can limit genetic diversity long-term.
However, there are also plants that, despite having hermaphroditic flowers, do not accept their own pollen; they are self-incompatible. For these plants, cross-pollination with a genetically different individual of the same species is the only way to produce viable seeds.
To find out the pollination strategy used by Corybas “Pollok” we conducted some pollination trials during its flowering season in August 2024. These included hand-pollinating some of the newly opened flowers by moving their pollen onto the stigma of the same flower with tweezers to see if they can self-fertilise. We also covered other flowers with cups to test if they would self-pollinate without being visited by a pollinator.
Our first results
After two months we returned to the site to see how the orchids and the pollination trails had fared. We found that three of the five self-fertilised orchids had formed fruit which we collected to take back to the lab. This suggests that Corybas “Pollok” is self-compatible, which is good news as it makes conservation efforts and research easier. The seeds we collected will be used in germination experiments.
There were no fruits other than the ones from hand-pollinated flowers, which suggests a low rate of natural fruit-set at the site and the need of a pollinator in order to form fruits.
We also discovered that some of the plants we had covered with cups were actually Corybas macranthus. Flowers of C. macranthus had not fully opened yet when we covered them up, and because the leaves of spider orchids are very similar, we did not realise they were a different species. Going forward we will have to be careful which plants we are working with now that we know that they grow in the same location, since they look similar when not in full bloom.
What comes next?
Next year I will continue this research into the pollination biology of Corybas “Pollok” and will focus on discovering the pollinator(s) of this unusual plant. Another question about the ecology of C. “Pollok” is which mycorrhizal fungi live symbiotically inside the orchid’s root and help its seeds to germinate and grow.
In preparation for answering this question, we took some root collar samples during our site visits, making sure to leave the tubers intact so that the orchids can resprout next season.
The next step is to extract coils of mycorrhizal fungal hyphae (known as pelotons) from these root samples and then culture these in the lab and sequence their DNA to identify them. I got training on some of these techniques at the Lions Plant Conservation Lab at Ōtari Wilton’s Bush in Wellington.
Isolating and identifying the right fungus can then help with germinating seeds under control conditions which can then be used to reinforce the population in the wild and create backup populations in case a catastrophic event destroys the habitat of the wild population.
Acknowledgement
A huge thanks to my supervisors Carlos Lehnebach, Bruce Burns (The University of Auckland), and Mahajabeen Padamsee (Manaaki Whenua Landcare Research) for their support as I start my research, to Tricia Aspin for her guidance and knowledge out in the field, and the landowners where these orchids grow. Another thank you to Karin van der Walt and Jennifer Alderton-Moss (Ōtari Wilton’s Bush) for teaching me the lab techniques they use when working with orchids. I would also like to acknowledge the Te Papa Foundation and thank them for awarding me their orchid conservation scholarship to help fund this research into Corybas “Pollok” and other spider orchids in Āwhitu.
