March in the hills with Barbara Mitcalfe and Chris Horne
Cyathea medullaris, mamaku, black tree fern
Early European settlers arriving in Aotearoa were astonished to see ferns-that-are-trees, a large plant form which they had never experienced. Raising elegant umbrellas on high, mamaku is our tallest, most massive, and probably our most distinctive tree fern species, with trunks c. 30 cm diameter reaching up to at least 20 m in deep, moist gullies. Their gracefully arching fronds can reach 6 m in length, and when they die and drop off, they leave distinctive, fibrous, hexagonal scars on the black trunk. These scars and the very thick, black stems of the fronds (up to 90 mm thick at the base and covered in scales with tiny spines) are features which distinguish mamaku from our other indigenous tree fern species, e.g. ponga (silver fern). When dried, these scales were valued as highly flammable tinder, carried as such by Māori when travelling.
We pause here to explain that, with experience, trampers can identify a mamaku from e.g., a ponga, simply by looking at the trunk. So when looking for bits of silver fern fronds to lay upside down as route markers, you can identify a ponga because instead of having hexagonal scars on its trunk like mamaku, ponga's dead fronds leave behind crowded, pale brown stem-bases c. 30 mm thick . We call them 'pegs' because they stick out c. 15 cm. all round the upper area of the trunk The handy mnemonic for this is 'P' for pegs, 'P' for ponga. We shall describe ponga in the April 2014 article.
Young mamaku fronds arise radially from the top of the trunk like spokes of a massive umbrella. They are called koru, or fiddleheads, frequently pictured in art works, their slow uncurling over several days a delight to behold.
Trampers might note that the external and internal medicinal (rongoā) uses of the pith / pitau are many. For example, raw or heated, when scraped, the pure white pith makes an excellent poultice, holding the heat particularly well and also having curative juices. 'Bush' remedies such as this are still being used with confidence in many areas today. Some bush workers even store pitau in their home freezer in case they need first aid in a hurry for a boil or a septic wound.
Mamaku is found in the Pacific Islands, from Fiji to Pitcairn. It is common in the North Island's lowland forests, mostly coastal in the South Island, but absent from the drier parts of Canterbury and Otago. It also occurs on Chatham Island / Rēkohu and Stewart Island / Rakiura. Wellington's most common tree fern species, it is often emergent above the canopy of regenerating forest. It prefers moist sites but is frost tender. You may have seen young mamaku fronds looking as bare as fish skeletons. This is because they are palatable to possums, who strip every shred of foliage off them.