This week’s plant of the week isn’t actually a single species, but rather a group of plants that have become endangered in New Zealand – the representatives of the Loranthaceae family, or mistletoes.
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Mistletoes are found throughout the world, and it often comes as a surprise that we have a number (8) of native species here, so absent as they are from public consciousness. Granted, they are certainly more well known in the South Island, where they are more common, but they are generally so rare nowadays, that they are almost unknown by most Kiwis. During my field trip last year to Australia, I couldn’t help but notice the huge amounts of mistletoes there, both in terms of sheer numbers and the number of species, even in the driest regions of the Outback: In any given area, at least one tree had a mistletoe growing into it; in some areas, every tree had one, often more massive than the tree itself.
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Like all mistletoes, the New Zealand species are hemi-parasitic. Mistletoe seeds are generally spread by birds, and germinate on host tree branches, often with their own complete portion of fertiliser. From there the seed grows into the branch of the host plant, tapping into the host’s vascular system to get access to sugars, nutrients and water. Over time, the mistletoe will grow and begin to photosynthesise on its own, relying less on the host plant for sugars, and more for its water and nutrient requirements. Like all parasites, mistletoes have negative effects on their hosts, and can severely restrict growth and reproduction. However, they are also recognised as a keystone species in most ecosystems, providing food and nesting sites for a number of animals, particularly birds.
New Zealand has Beech-, Green- Dwarf-Mistletoes. The Beech Mistletoes, as their name suggests, comprise three species (Peraxilla tetrapetala, P. colensoi and Alepis flavida that predominantly parasitise the native southern beech species (Nothofagus spp.), although they are also found on other native species including Tawheowheo (Quintinia serrata) The two Peraxilla species have bright red flowers in Summer, which in older times would turn entire mountain ranges red at Christmas. The Green Mistletoes are perhaps less charismatic but far more generalised than the Beech Mistletoes, and one species, Ileostylus micranthus has been recorded on over 200 host species, including totara and the Pittosporum species.
The main threat to our native mistletoes are possums, which is not unsurprising given the damage that the barstards have done to many of our plants and ecosystems. Mistletoes have declined hugely in range over the last 100 years, and are now entirely absent in many areas where they were previously common. Possums browse the flowers, leaves and shoots of mistletoes, removing vital food source for native birds such as tuis and bellbirds, which in turn act as pollinators for the mistletoes. As a result, not only do the mistletoes disappear, but bird populations also begin to suffer. Many areas that have effective long term possum population control (through 1080 drops) have had remarkable restoration of their mistletoe populations.
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