Making a case for the 5th kingdom
Are fungi plants? Are they animals? How do you decide?
Mycorrhizae
The mycorrhizae is a structure that is formed by the symbiotic relationship between fungi and plant roots.
Since the 1700s when it was first used, the classification system for organisms has been under debate. As new species have been discovered and old species studied in more depth, scientists have had to reassess how things are related.
In 1969, a scientist named Robert Whittaker published the first major revision to Linnaeus’s proposed two kingdom classification – animals and plants (which included fungi). In the revised version, Whittaker suggested that fungi should be classified as a separate kingdom, and this has been accepted by scientists.
Are fungi plants or are they animals?
Fungi share characteristics of both plants and animals, making it confusing when trying to classify these organisms.
Fungal kingdom
Dr Peter Buchanan, of Landcare Research NZ Ltd, introduces the wonderful world of fungi. There are more fungal species than there are plant species, and they have a range of roles, both positive and negative. Fungi are important recyclers of nutrients in the forest and help plants take up minerals from the soil.
They seem to reproduce like plants by producing spores (that could be likened to the production of seeds). They have root-like structures to absorb nutrients (hyphae), and like plants, they don’t change their position, instead relying on spore dispersal to colonise new areas.
But some features make them more similar to animals. They can’t produce oxygen via photosynthesis and they absorb oxygen through their body surface. Like animals, they excrete waste out onto surrounding surfaces, and they need a food source.
There are lots of them!
The kingdom fungi is now thought to encompass around 1.5 million different species. Moulds, yeasts, slimes and mushrooms are all fungi. In fact, there are more different types of fungi than there are species of plants.
Nature of science
Science knowledge develops over time. When scientists find out new information or see existing information in a different way, they propose new explanations. Sufficient evidence leads to changes in understanding.
Scientists in New Zealand have identified around 7,500 fungal species but estimate that this is only about 35% of the total number of species that inhabit New Zealand.
This means there are still about 17,500 different types of fungi growing in New Zealand that are yet to be found and identified.
So what do fungi do?
Fungi are recyclers, breaking down material from plants and animals to enable the nutrients to be returned into the ecosystem.
Dog vomit slime mould
The kingdom fungi includes mushrooms, slimes, yeasts and moulds. This example is Fuligo septica – commonly referred to as dog vomit slime mould.
One example of this class of fungi is the mushroom – the fruiting body or reproductive stage of many different types of fungi, often cultivated for food. Mushrooms come in an enormous range of colours and shapes. Many are tasty, but some are poisonous.
Some fungi also exist in a symbiotic relationship with plants, helping them to absorb nutrients from the soil. Specialised types of fungi form mycorrhizae – sock-like structures over the smallest roots of plants. Many plants have these structures, which are generally invisible to the naked eye.
The fungus extends hyphae (very thin threads) into the soil surrounding the plant root and absorbs essential nutrients such as minerals and water. Some of this is used by the fungus, but much is absorbed into the plant, helping it to grow. In return, the fungus absorbs some of the sugars that the plant makes during photosynthesis, which helps the fungus to grow. This forms a mutually beneficial or symbiotic relationship where both the fungus and plant are healthier.
Student activities
In the activity Observing fungi, students hone their observation skills and practise using the science capabilities ‘Gather and interpret data’ and ‘Interpret representations’.
In this quiz, students can test their knowledge of fungi online or in a paper-based quiz. The quiz can be used as an introductory tool to gauge students’ prior knowledge, as a summative assessment or as an engaging treasure hunt to introduce students to some of the different features, parts and uses of fungi.
