Epiphytes & Parasites Part Deux

Who does't like a good two part-er? You have read the first part right??? If not, you can check it out here.

Caught up now? Ok let's continue...

So we've learnt that the sweet, sweet Pineapples are bromeliads and that bromeliads are epiphytes. Which are plants that reply on other plants for support, to grow on, without any firm grip on the earth and no reliance on soil for nutrient and water. Many types of ferns and orchids are also epiphytes.

A common & popular Epiphyte - the Elkhorn.

In this installment of Ephiphytes & Parasites we look at the latter of the two and delve into the darker side of how plants can manipulate others for their own advantage. Parasitic plants generally have a negative effect on the growth and life cycle of their hosts by using them for more than just physical support, they also tap into their vascular tissue (plant veins) and steal their nutrients and energy.

Parasitic plants need to germinate in close proximity to their hosts, so they can attach themselves to ensure their survival and growth. Some parasitic plants are even clever enough to 'sniff out' their hosts by being able to detect certain chemical 'scents' host plants give off in the surrounding soil.

There are two types of plant parasites: stem - who attach and grow on the above ground parts of the host and the root parasites - that attach themselves to to the root system of their host. In both cases, once the parasite has coupled with the host, they begin to steal their food and water.

The first plant we'll cast the spotlight on is the group of Ficus (Fig) species known as strangler figs. This common name conjures up images of some kind of nocturnal serial killer but fear not, strangler figs only target other trees and palms.

Now these group of trees are actually an epiphyte, technically classed as a hemiephyte (only spending part of it's life as an epiphyte). It is the potential of these figs to kill others that makes me view them as more parasitic than epiphytic.

The tasty fig fruit is swiftly eaten by birds and dispersed into the canopy of nearby trees. The seed then germinates in the arches of tree branches and begins sending it's aerial roots towards the ground. It's in these early stages that these figs are more like true epiphytes.

The beginning of the end?

This diagram explains the life (and death) cycle of the strangler fig.

In general most Ficus sp. are quick growing. The aerial roots of the strangler fig rapidly descend towards the forest floor, becoming the first anchors and at this point it begins to gather soil water and nutrients, speeding up the growth process. It's not long until the fig will begin to wrap it's multiplying roots around the host plant, holding it tighter than any lovers embrace.

They grow up (and over) so quick!

The fig "take over" looks a bit alien but you have to tip your hat to the awesomeness of mother nature, she sure has equipped some of her 'children' with some pretty handy tools for getting on with life! Due to the fig being more aggressive than the host, the support trees can't compete as strongly for food and water and therefore can't produce new foliage to capture energy from the sun, in most cases they will slowly die out.

Even the end result is pretty impressive:

Inside the hollow, where a host once was.

Up next is a serious weed of agricultural significance. Dodder is a true plant parasite that has a nasty habit of infecting and smothering it's hosts to their untimely deaths. In Australia it causes problems in lucerne pastures and broad leaf and seed crops, contaminating production and reducing yields.

There are over 100 species of Dodder around the world, mainly in temperate and tropical regions. They produce small pink, yellow or cream flowers that produce an abundance of small seeds, that can lay in wait for up to 10 years in the soil. The plants themselves are leafless, having leaf modification resembling minute scales.

Most Dodder species can only produce small amounts of chlorophyll (or none at all), hence their reliance on other plants to get their nutrient requirements.

Who ordered the pasta?

Dodder (Cuscuta sp.) seed germinates close to their hosts by sensing and reacting to chemical cues of potential hosts plants.  They soon intertwine their climbing tendrils with the stems of other plants. These leafless stems then produce Haustoria, a root like structure that pierces and grows into the stems of the host drawing out nutrients.

Got it wrapped around your finger.

Dodder then rapidly grows, spreads over and blankets everything in it's path, not only suppressing growth by stealing nutrients but by smothering & restricting the growth of other plants. In a lot of cases Dodder can be fatal to the host and in crop production losses of up to 10% due to Dodder parasitism or suppression is not uncommon.

Lastly, one of my favourite parasites. Sorry if I have given the previous contestants a bad wrap, I promise that the next one will leave you feeling a bit more warm & fuzzy.

The group of parasitic plants known as Mistletoe's occur around the world. I have been fascinated by theses plants for a long time and more recently my interest was rekindled during a trip to Germany in December 2015.

These species , most likely Viscum album have a more globular habit, forming dense balls and look like decorations in deciduous trees as you can see below:

But I think us Australian's have the prettiest of all Mistletoe's. Down Under we have around 90 species, seventy of which are native. They occur in a wide range of hosts plants, both native and exotic. It can be difficult to spot them in evergreen trees, especially native host trees as they can mimic the leaf size & shape of their hosts. It is much easier to spot them in the canopy of deciduous trees throughout the cooler months without leaves to hide behind.

Mistletoe's are semi-parasitic as they have chlorophyll in their leaves to produce energy for growth but instead use their hosts like a surrogate root system, for support and water.

The amazingly pretty Long Flowered or Apostle Mistletoe 

Many of our native mistletoe's are beneficial to a wide range of wildlife - their foliage, flowers and fruit all are highly nutritious. It's the fruits I'd like to look at now, one of the most interesting things about mistletoe's is the way it has it's seed dispersed.

The seed is encased in a very sweet & sticky fruit which birds love! Birds will devour the fruit like a kid with candy. The fruit is digested fairly quickly through the little stomachs of our winged friends, unfortunately (and somewhat comically for the birds) the seeds remains fairly sticky on the way out!

The male Mistletoe Bird - looks like he wants to dance!

What happens next is a very interesting little dance the birds do to dislodge said seed, check it out here. Once stuck in place, the seed quickly germinates and taps into the lifeblood of the host tree.

It is rare that mistletoe's will cause death in their host's, when it does occur it is generally because the tree was already in poor health. If you must remove the mistletoe, simply remove the branch it's living on. Though I urge you at least to see it's floral display.

So there you have it, a little look at the world of parasitic plants. Some deservedly have a bad reputation, whereas others get an unfair label. But all in all they do deserve a little appreciation, they have evolved to take advantage of others for their own benefit, it's these survival mechanisms that make plants  interesting and worthwhile of further study - who knows what they secrets they still have left for us to discover???