Mistletoes are plants that live on, and parasitise, other plants. They produce some of their own resources through photosynthesis but they also tap into the resources of their host through special roots called haustoria. They are therefore classed as "stem hemi-parasites".

We have eight spectacular mistletoe species in New Zealand that belong to three groups: beech, green and pygmy mistletoes. The beech mistletoes almost always grow on beech trees and have great displays of bright flowers. The green mistletoes are less specific in their host preferences and have less colourful flowers, and the pygmy mistletoes are very very small and hard to spot amongst their scrubby host trees.

Why are our mistletoes spectacular? Because they are SO interesting!  Here are 5 facts to prove my point. For more information I suggest exploring the University of Canterbury Mistletoe Research Group webpage.

1. The two Peraxilla species in the beech mistletoe group have beautiful flowers that can only be opened by birds or bees who tear the top off the fused petals, allowing the flower to burst open and spray the pollen over the face of the bird or if lucky, the body of the bee. Check out this video! (you might have to slow it down to see the action - the bellbird is best).

2.  The specialised roots of the mistletoes penetrate the host stem and remove enough resources to assist their growth but not so much as to kill the host. 

3.  Six of the eight species are endemic - they occur only in New Zealand and have adapted to our weird and wonderful ecosystems.

4.  The pygmy mistletoes have mildly-explosive seed dispersal mechanism. Flesh of the fruit is like an open-ended cylinder and when it begins to ripen the tissues swell and eventually build enough pressure to eject the seed.

5.  As discovered by the Canterbury Mistletoe team Our mistletoes are some of few NZ forest species to benefit from forest fragmentation. This is attributed to two factors: 1) the mistletoes do well in high-light environments and 2) the native caterpillar that predates on their flowers (Zelleria maculata) does not do as well in fragments. 

If you've ever done a google scholar search for "epiphytes" you're probably aware that forests/terrestrial systems are not the only places where epiphytes exist... the marine world has them too! 

So what are marine epiphytes? As in a terrestrial system, they are organisms that live on plants. But unlike a terrestrial system, the "organisms" are not necessarily plants. This seagrass website sums it up well: 

"Epiphytes of seagrasses include algae (micro and macro), bacteria, fungi, sponges, bryozoans, ascidians, protozoa, hydroids, crustaceans and mollusks."

Algae epiphytes are common and can densely cover the leaves of plants like seagrass. This is called "biofouling" - probably because it turns the clean, green grasses a bit cloudy and brown. These marine epiphytes are grazed by organisms such as snails and if the balance of host/epiphyte/grazer is not in check, the host plants can be smothered by epiphytes and prevented from photosynthesising. 

This all sounds a bit foreign when we compare it to forest systems - I couldn't possibly consider a tree loaded with epiphytes to be "fouled" and we don't consider forest animals to be epiphytes. However, there are also similarities:

• both systems have holoepiphytes and hemiparasites
• epiphytes add to ecosystem biomass and biodiversity
• epiphytes contribute to nutrient cycles and affect light interception
• epiphytes provide an important food source for fauna in either fruit or foliage
• it is often the oldest host or part of a host that has the most epiphytes

It seems that there has been very little comparison of marine and terrestrial epiphytes - I think it could be a very interesting future research direction.

Winter may not always bring the best weather for outdoor adventures, but it can bring excellent opportunities for epiphyters. A few of us recently went for a hike on Mt. Pirongia, and were surprised at what we found!

Not long after we began our ascent, we were excited to find a beautiful mass of Huperzia varia that had fallen off its perch, lying right beside the track - an excellent opportunity to look at it up close. I was surprised to learn that the plant does grow quite large, and the foliage feels very soft, unlike the similar looking, scratchy leaves of rimu.

Later on, we came across a large branch lying on the track. Another casualty of the recent stormy weather. To most, a fallen branch is simply something to step over or walk around, but to those who appreciate the canopy dwellers there is more than meets the eye. The branch was covered in a dense moss cover which provided a perfect substrate for the roots of Earina to gain hold and obtain resources.

As we made our way back towards the carpark, a fellow tramper notified us of a fallen tree further along the track. Once again, he regarded this as an obstruction, but Catherine and I were happy for another chance to see some epiphytes up close! It turned out to be half of the main trunk of a large pukatea. It was difficult at first to decide what the host was, as there was a mass of foliage on the ground full of epiphytes. The branch was full of Rubus so we were hesitant to get too close, but we could see that there was a huge number of species living in that tree!

Without climbing any trees, we had a great chance to see some epiphytes from the ground! Although we prefer not to have the wind and rain, we can be witness to the process of succession, and be thankful for bringing those epiphytes down to our level!

Last Friday, a few epiphyters got together to practise some tree climbing. We climbed some eucalypts and noticed a stark absence of epiphytes, vines, mistletoes... there wasn't even significant moss or lichen! (the light shading of green on some bark could be moss?). We attributed the host tree nakedness to the bark-shedding habit of this species.

But not all exotics are poor hosts, for example, Pinus radiata was recorded as a pretty good host by Colin Burrows in Westland and the following photo is of a Griselinia lucida shrub established in a pine in Pukekura Park, New Plymouth.

A hard-working epiphyter in Te Aroha has shown that a Quercus palustri can be a superb host for a range of native and exotic epiphyte and even non-epiphyte species. Check out his amazing "epiphyte tree".

Given the choice, it must be better to have native trees for hosting epiphytes, vines and mistletoes because they are more likely to have complimentary life cycles. For example, a tawa host tree provides fairly consistent habitat conditions for an epiphytic species because it is evergreen and thus light levels and quantities of leaf litter are steady throughout the year. In contrast, the habitat conditions in a deciduous exotic host tree will vary with the seasons.  This may not necessarily be detrimental to native epiphytic species but it is not conducive to the establishment of a natural community. I'll leave it there because I could ramble and speculate all day but I do think an exotic tree is better than no tree!

I'll leave you to contemplate the importance of exotic trees for epiphytes with a nice photo taken from a lovely gum :)