Epiphytes, Parasites and Symbiots


The term 'Parasite' is one that we are all reasonably familiar with, an organisms which lives on, or in a host consuming it, often causing its death (Tapeworms and Taxmen) Epiphytes, from a botanical standpoint are plants, or other organism which lives on, but does not consume a host. Orchids and Bromiliads are epiphytes, mistletoe and some fungi are parasites.

Symbiots as we shall see are equally difficult to define.


Epiphytes

One of the most easily recognised epiphytes is the Orchid. In the wild the vast majority are found perched on branches, or trunks, with their fleshy roots trailing down. They are however a varied order and here in the UK can be found growing in grassland and bogs.


Not all fungi are harmful to your trees, all plants have a symbiotic root fungus called Mycorrhiza which benefits the tree. It can usually be seen as a thin white sheet around the roots on repotting and is particularly noticeable on Pines.

Mycorrhiza becomes an active part of the root system, transferring nutrients into the root system in exchange for sugars from the plant, indeed there is strong evidence that mycorrhiza acts as a pathway for nutrients from adult trees in the forest to seedlings on the forest floor.

Bearing in mind that the mycorrhiza and host form a mutually beneficial union they have a what's termed a 'Symbiotic' relationship.

Here we have the mycorrhiza fruiting. The natural response from gardeners is to panic if they see this, I'd panic if I didn't, it's the sign of a healthy tree in a healthy environment.


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Mosses and Lichens are epiphytes, using branches and trunks to grow on. The Lichens (shown right) are good indicator of air quality, as they won't grow in polluted environments


Parasites

The term Parasitism is perhaps less easy to define. Mosquitos are not considered parasitic, as they do not live in. or on their host, The femails only taking blood to fuel egg production. Parasites generally eat, while living in, or on a host, either food consumed by the host, or the host its self.

To the right we see a Cat flea taken from one of my long dead moggies, a typical Parasite (the flea not the cat?)

Photo A.C.Roffey 1982


The parasitic wasps, the Ichneumon Wasps are also widespread

Adults vary in size from 1/8 to 1-1/2 inches with long, many-segmented antennae and long, slender bodies. Females have long ovipositors (egg laying tubes), the longest of which are six times the body length. Legs are long and slender. Yet again they, or rather their larvae eat caterpillars, or grubs.

An ovid female will capture a grub and paralyse it, it will then using its egg laying tube (ovipositor), insert an egg into it and the lucky grub will then be eaten from the inside.

The females of those species with long tubes, will listen for grubs moving in wood and probe with their tube until they locate their prey, injecting an egg into it.


Symbiots

This is another term that covers a fair bit of ground

We've already looked at Lichens, but i've returned to them as not only are they epiphytes, but are most certainly symbiots.

The Lichen as such is not a single entity, comprising of a symbiotic relationship between and this is where it gets complex! either a bacteria (cyanobacteria) or an algae, with a fungus. We saw the fungus mycorrhiza forms a symbiotic relationship with plants, well Lichens take this one stage further, co-habiting in the same body. It's how the first multi-cellular organisims evolved.

To be a symbiotic relationship both partners must benefit.


Symbiosis Allen. C. Roffey 23:10 14/01/2008