How to use a simple key

Key to the common eucalypts of Clearwater

Introduction

Apart from koalas and kangaroos, there is probably nothing more Aussie than a gum tree. Many poems and songs have been written about this particular tree.

Gum trees are known as eucalypts and there are more than 600 recorded species. From alpine forests to deserts, eucalypts have survived and flourished in Australia's varied climates. So while they are all related - they are in the genus Eucalyptus - and have many characteristics in common, there are differences. And it is these differences you will be looking at in order to 'key out' or identify a particular specimen.

Let's start by looking at the general characteristics of eucalypts.

Characteristics

Eucalyptus flowers have:

• an operculum instead of sepals and petals
• many stamens
• an inferior ovary.

Eucalyptus flowers are arranged in umbels.

The operculum or bud cap:

• covers the stamens
• is formed from the fused sepals and petals
• has many different shapes (eg domed, grooved, long and curved or rounded).
• may be short or long.

Eucalyptus leaves are often:

• tough
• sclerophyllous
• glaucous.

Juvenile leaves often look different from the mature leaves.

Many eucalyptus or gum leaves smell when crushed.

The fruit or capsules are commonly called gum nuts. They are woody and have a variety of shapes including:

• globular
• pear-shaped
• urn-shaped
• bell-shaped.

Bark

The type of bark can be particularly helpful when identifying plants and sometimes appears with cracks or fissures. For example:

• thick, deeply-furrowed bark - ironbark
• rough bark which peels off in long pieces - stringybark
• bark which peels off in patches to leave a spotted appearance - spotted gum
• mottled red, grey and white - river red gum.

Other features

• epicormic buds
• lignotuber

Other terms

• mallee
• bloodwood
• resprouters

Below is part of a key for the eucalypts of the Clearwater area.

A key consists of a series of statements or descriptions of the plants involved. The statements are grouped in pairs and each pair requires a choice to be made. This leads to another pair of statements where another choice is needed.

It's a bit like playing a game - proceeding from one choice to another until you arrive at the answer. The plant is said to be 'keyed out'. Keys such as this are called dichotomous keys.

KEY FOR PLANT PLANET EUCALYPTS

Leaves concolorous
	Number of flower buds per umbel 7 or more
	Bark smooth.......... E. camaldulensis
	Bark rough at least at base.......... E. rudis
	Number of flower buds per umbel 3
		Leaves opposite: stamens yellow.......... E. erythrocorys
		Leaves alternate: stamens pink or white
			Leaves lemon-scented when crushed......... E. citriodora
			Leaves not lemon-scented when crushed......... E. leucoxylon

Leaves discolorous
	Bark rough throughout: fruits 2-4 cm wide.......... E. calophylla
	Bark smooth, sometimes rough at base: fruits <1 cm wide
		Valves projecting from fruit incurved.......... E. grandis
		Valves projecting from fruit erect to outcurved.......... E. saligna