Sphaeropteris medullaris
This month’s plant of the month is the largest tree fern species in Aotearoa (and possibly the world!); mamaku, also known as the black tree fern. Mamaku is a tall emergent species, and are incredible plants that can be spotted towering up to 20m tall in the canopy, with a frond spread of up to 14m across. They can be found growing in a range of forest types, both native and exotic. These ferns can be abundant in the initial forest formed on slips and other disturbed sites undergoing regeneration, and tend to be a frost-tender species, preferring damp habitats. Mamaku grow in ngahere from sea level to 600 metres in elevation on the Three Kings Islands, throughout the North and South Islands, Stewart and the Chatham Islands. Mamaku are also native to Tasmania, Victoria and some Pacific Islands. More locally in Tāmaki Makaurau they can be commonly spotted in the Waitakere Ranges, Hunua Ranges and Coromandel. Mamaku can be found in the wetter areas of Kaipātiki, too, such as in Eskdale Reserve, Le Roys Bush and Witheford Reserve. Go for a local stroll in any of these spots to meet our plant of the month in-person!
Tree ferns are fascinating and iconic species that are part of what makes Aotearoa’s ngahere so unique with their long fronds, distinctive crowns and intriguing 'trunks’ - which are actually a fibrous mat of aerial roots that need to be kept moist, too! Tree ferns are ancient plant species, having existed for around 360 million years - over 100 million years before dinosaurs came to be. The 'great fern radiation' 150 million years ago led to the widespread diffusion and speciation of tree ferns. But like most flora and fauna they suffered in the mass extinction event at the close of the Cretaceous period (145-65 MYA), leaving fewer species behind. Today, Aotearoa is home to ten native tree fern species, the most frequently seen species of which are the silver fern (one of our most-known kiwiana icons!), mamaku, katote, and wheki.
Mamaku are associated with a common thread of bringing life into the world and supporting it through birdlife, rongoā Māori, and through relationships with other plants in the forest/ngahere.
Hihi/stitchbirds are one of Aotearoa’s rarest bird species, with around 2000 birds left in isolated pest-free sanctuaries on islands around the North Island, mainly Little Barrier, Tiri-tiri Matangi and Kapiti Islands. Hihi are small nectar, fruit and insect-eating birds that are particularly vulnerable to a range of introduced predators and diseases, and have complex behavioural and mating biologies that are now well-studied in order to conserve the species.
Hihi build much of their nests with fibres from mamaku. Their nests’ foundations are composed of tough, matted aerial root fibres from mamaku trunks, and they furnish their nests and protect their eggs with fibres collected from the koru (the spiral-shaped new fern frond). Thus, these birds rely closely on mamaku to help raise their young.
In rongoā/Māori medicine, mamaku is important after childbirth. The bruised pith has been used as a poultice to relieve inflamed breasts and it was also thought to be highly beneficial to the child in the womb when eaten by pregnant women, and a tonic produced from boiling fronds aids in the discharge of the whenua/placenta. Sap emitted from cut fronds has also been used to aid in a wide variety of skin conditions and issues. Baked in a hangi, the pith from the upper part of the mamaku trunk and also from the stipes of young fronds was eaten both as a famine food and as a special relish at feasts. Thus, the mamaku has been a significant source of food and medicine throughout Māori history.
Mamaku trunks also support new life through being aerial plant ‘nurseries’. The seeds of several plant species have been observed germinating and growing as seedlings and saplings amongst the fibres of mamaku trunks, including kawakawa and rangiora. Whilst many of these epiphytic seedlings may not make it to adulthood due to limited root space, a number (such as rātā and pōhutukawa) are able to grow their roots down to the forest floor and become trees of their own. The fallen fronds of mamaku also decompose to provide rich soil that supports the surrounding plants in the forest and helps young nutrient-hungry seedlings to become large trees. The fibrous trunk of mamaku and other tree ferns is also perfect habitat for a number of insects to live amongst - what an abundant and supportive species to have in the ngahere!
At Pest Free Kaipātiki, we focus on reforestation in reserves, lobbying of local government bodies for greater tree protection, and invasive pest control to ensure that our ngahere are diverse and protected for future generations. Join us to help out nature by trapping in your backyard or by getting involved in plantings and working bees at reserves near you!
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