By Spencer Shaw, Brush Turkey Enterprises
Mention mistletoe to some folk and they will cross themselves, produce wooden stakes, silver bullets, cloves of garlic and sprinkle holy water about liberally. The thought of a plant drawing on the bodily fluids of another plant for its survival conjures up images of herbaceous vampires sucking the life out of our trees. And lets face it being described scientifically as a parasite just doesn’t generate any good press.
What possible good could these little triffids be doing out there in nature I hear you say? Well I’m glad you asked.
There are 25 species of mistletoe in the family LORANTHACEAE and 8 species of the family VISCACEAE found in SE Queensland and also for good measure 10 species of the tree or shrub ‘mistletoes’ of the family SANTALACEAE. These plants may draw on the moisture and mineral reserves of their hosts but what many of us may not notice is what they give back to the greater ecological community and the many species of animals and insects that depend on them, some almost exclusively. Research is now showing that mistletoes are a keystone resource in forests and woodlands worldwide. Mistletoes provide the habitat enrichment on which numerous species depend. Mistletoes have a disproportionate effect on the structure and function of forested ecosystems in relation to their size, resulting in increased biodiversity in most habitats.
So why have mistletoes been given such a bad rap? Well besides the whole ‘parasite’ label being slapped on them, there are perhaps awful memories of Christmas parties where you where forced to kiss someone who you really didn’t want to even shake hands with under the mistletoe! Mistletoes can get out of hand in some environments contributing to tree weakening or death, but as with most natural imbalances they are not the cause but the symptom of greater ecological imbalance – usually caused by, you guessed it Us! Perhaps the predators of mistletoes are reduced in some disturbed environments or conditions are more favourable for the mistletoe birds that are their major agent of dispersal. Mistletoe birds are represented in Australia by a single species Dicaeum hirundinaceum. These little birds are mistletoe specialists with a specialised digestive system that can draw enough nutrients from the sticky pulp of the fruit but pass the seed through their digestive tract within a ½ hour (now that’s what you call regular) completely unharmed. The seed of mistletoe have a long sticky tail that passes through the digestive system. This long sticky tail requires that the little birds wipe their backsides on a branch as they pass the seed to completely pass the seed tail. This ensures that the seed is placed in the best position for it to grow, on a branch. The seed tail also helps it adhere to the branch. Several other birds such as honeyeaters, silver eyes also eat the fruit of mistletoe and many birds, possums, sugar gliders etc. take advantage of their nectar rich flowers for a quick sugar hit. There is also another intriguing set of animal – mistletoe relationships between mistletoe, ant and butterfly. Most of the butterflies known as ‘Azures’ of the genus Ogyris are exclusive mistletoe feeders and many also require the presence of specific ants. These butterflies and ants have co-evolved in the presence of mistletoes. The butterflies provide a variety of compounds (amino acids) secreted from glands on the caterpillars to the ants, and in return the ants provide protection to the caterpillars. Some Azures caterpillars hide under bark or in borer holes and some caterpillars hide in the ant nests during the day, and at night in the company of ants travel upto a 40 metre return journey, to mistletoes high up in eucalypts.
Mistletoes are at their most diverse in Eucalypt and Dry Rainforest communities and in these areas mistletoes are often quite specific in what plants they will use as hosts. More amazingly their leaves often mimic those of their host such as Amyema cambagei the She Oak Mistletoe with its needle like foliage that lives on Casuarina and Allocasuarina sp. There are even mistletoes that are specialists in ‘out mistletoe’ing other mistletoes’ such as Notothixos subaureus the Golden Mistletoe that lives exclusively on other mistletoe’s. One mistletoe species that does make a living in our local rainforests is Amylotheca dictyophleba the Rainforest Mistletoe, they have very attractive upright red flowers that attract a variety of wildlife and live on a wide variety of rainforest trees. I recently saw on the Mooloolah River an Aphananthe phillipensis or Native Elm playing host to A. dictyophleba that was in turn playing host to N. subaureus. I’m sure if I had looked closer there would have been some ants and some caterpillars, a flash of red as a male mistletoe bird took flight and the smell of brushtail possum pee from the previous nights feeding.
So next time you see a Mistletoe don’t panic – the apocalypse isn’t upon us. They are an important part of the intricate web of life and if we keep playing with the threads we will all come undone. It could even be argued that it is worthwhile “planting” mistletoes on our gardens and reveg’ plots to enhance diversity and return them to areas they have disappeared from through land clearing. But that’s another story.
Some Local mistletoes and their hosts
Amyema cambagei on Casuarina, Allocasuarina sp.
Amyema congener on Acacia, Casuarina, Callistemon sp.
Amyema conspicuum on Alphitonia excelsa
Amylotheca dictyophleba on various Rainforest and Camphor Laurels
Notothixos subaureus on other mistletoes
Dendrophthoe vitellina on various tree species mainly Myrtaceae
