Classifying and identifying ferns
Scientists currently consider that New Zealand has approximately 230 species of fern in about 50 different genera. They are widely distributed throughout the country, including around 42 species that are found on all 3 main islands. These are ferns you may know and recognise. Their common names may be familiar to you (silver fern, hen and chickens fern) or perhaps you know their Māori name (ponga, mouku).
Fern rhizomes
When classifying fern species, vegetative characters such as the rhizome become important. The rhizome is the stem of the fern plant. It can be creeping, vertical or erect.
Botanists and other scientists document the characteristics of these ferns for classification and identification.
Fern characteristics
The structure of ferns are quite simple, and scientists begin by observing and documenting their sporangia, rhizomes and fronds.
The reproductive structures are the most important characteristic for classifying ferns. When you turn over a fern frond and look at the sporangia on the underside, you’ll quickly see that they are grouped together into various shapes and patterns. Sporangia can be grouped together into circles, elongated along the veins or arranged around the margin of the frond. There are numerous patterns and variations.
Parts of a fern
Dr Patrick Brownsey from Te Papa shows us the 3 major parts of a fern: the rhizome (the underground stem), the leafy frond and the sporangia (the reproductive structure).
Points of interest:
What are the 2 functions of a fern frond?
For more in-depth coverage of fern structure, visit the Fern structure and Underlay of a fern interactives.
In addition, some sporangia are protected by a little membranous structure (an indusium), and others aren’t. These characteristics help us to sort out which family and which genus the fern belongs to. Watch this video to learn more about fern reproduction.
For species, the vegetative characteristics become important. Is the rhizome creeping, vertical or erect? What is the shape of the frond? Is it highly divided or is it undivided? If it’s divided, to what degree is it divided? In addition, characteristics like whether there are hairs on the surface or not can also be useful.
Microscopic examination of spore shape and size and molecular analysis of fern DNA are two other techniques that are utilised.
Classification
Classification helps us put order into the world around us. Humans have been doing this for centuries. Classification provides a robust framework in which we can identify plants. In turn, this allows us to organise herbaria, retrieve information and undertake further study on plants.
Classifying ferns
Taxonomy is the science of classification. Dr Patrick Brownsey from Te Papa explains how botanists use reproductive structures (sporangia), vegetative characters (rhizome and frond shape) and microscopic characters (spore size) to classify ferns.
Point of interest:
The evolution of land plants diagram featured in this video is found in the article What is a plant?
The Linnean classification system places organisms within hierarchical groups that show their relationship to other organisms. Botanists and plant scientists rely on this system.
This is the classification for the hen and chickens fern:
Kingdom
Plantae
Division
Tracheophyta
Class
Polypodiopsida
Order
Polypodiales
Family
Aspleniaceae
Genus
Asplenium
Species
bulbiferum
Starting with the plant’s unique two-part Latin name (genus and species), the plant’s relationships to other plants is determined as you move up to family, orderclass and division within the plant kingdom.
Identification
Every identified and classified organism has a unique two-part Latin name. The hen and chickens fern has the unique name Asplenium bulbiferum.
Linnean classification system.
The Linnean classification system places organisms within hierarchical groups that show their relationship to other organisms. Note that, when classifying plant, division rather than phylum is the term used for the second grouping.
Two-part naming, also called binomial nomenclature, forms the basis of the modern classification system devised by Swedish botanist Carl Linnaeus in 1753. This orderly system gives each plant a ‘generic’ name (genus) and then a ‘specific’ name (species). In this system, the silver fern is known as Cyathea dealbata (the species name is descriptive meaning ‘white washed’), and the hen and chickens fern is known Asplenium bulbiferum (the species name is descriptive meaning ‘bearing bulbs’).
Today, the naming of plants is governed by a set of rules and recommendations produced by the International Code of Botanical Nomenclature (ICBN). Its intent is that each taxonomic group of plants has only one name that is accepted worldwide, thus reinforcing the value of a unique scientific name.
Why are ferns unique?
Dr Patrick Brownsey and Dr Leon Perrie from Te Papa explain why ferns are unique among land plants. Ferns have 2 independent living structures within their life cycle – the sporophyte and the gametophyte.
Point of interest:
How does the gametophyte of a flowering plant differ from the gametophyte of a fern?
Nature of science
Scientists need to communicate their ideas and share information in an accurate and clear manner. By using binomial nomenclature, scientists avoid confusion around common or multiple names given to organisms.
Activity idea
DIY fern classification uses fern specimens or image cards to group fern species according to their physical structures – rhizomes, fronds and sporangia.
Useful links
Classification is not a field that stays still. With technological developments and improvements – such as genetic sequencing – new information is becoming available. This means scientists and taxonomists sometimes have to reassess classifications. Learn more in Leon Perrie's thought provoking blog, Why do scientific names change?
Here is a simple guide to identifying our native tree ferns by Leon Perrie.
