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An Introduction to the Eucalypts

The Genera Eucalyptus, Corymbia and Angophora

Prepared by Andrew Lyne

Introduction

The publication in 1995 of a scientific paper recognizing the bloodwood and ghost gum groups of the eucalypts as the distinct genus Corymbia has resulted in a little turmoil in eucalypt taxonomy (see here for a paper with more details on Corymbia). Whilst many herbaria and botanic gardens recognize the bloodwoods and ghost gums as species belonging to Corymbia, here at the Australian National Herbarium we do not - the bloodwoods and ghost gums remain as species of Eucalyptus. Despite the taxonomic contention, Corymbia is included here so as to provide readers with some understanding of the alternative taxonomy.

This document aims to present a simple introduction to the uniquely Australian group of plants, the eucalypts, a common reference to the three genera Eucalyptus, Corymbia and Angophora (Hill & Johnson, 1995). These closely related genera are in the family Myrtaceae which, worldwide, comprises some 155 genera and 3000 species.

Myrtaceae is found mainly in Australia (c. 75 genera and c. 1400 species), Central and South America (c. 45 genera) and Malesia (c. 30 genera). In southern and central Africa there are 4 genera, whilst in the Saharan region of Africa and the Mediterranean, there is only one genus, Myrtus (which also happens to serve as the type of the family). An account of the family can be found in Morley and Toelken (1983).

The first botanical collections of Eucalyptus, Corymbia and Angophora were made by Joseph Banks and Daniel Solander in 1770. They collected specimens of Corymbia gummifera (the Red Bloodwood, formally Eucalyptus gummifera and before that Metrosideros gummifera) from Botany Bay, New South Wales and Eucalyptus platyphylla from Endeavour River, north Queensland. It was not until 1788 however that the first species of Eucalyptus, E. obliqua was named by L'Heritier, a French botanist who was working in London at the time.

Thus, in this document the term eucalypt is used collectively to include the genera Eucalyptus, Corymbia and Angophora.

Here are some views of the Eucalypt Lawn at the Australian National Botanic Gardens in Canberra - [photo 1] [photo 2].

Classification

The eucalypts can be distinguished from other Myrtaceae by their possession of either a calyptra (operculum) (in the genera Eucalyptus and Corymbia) or petals with very broad bases (in the genus Angophora).

See here for a short paper on Corymbia. The paper outlines why the bloodwoods and ghost gums have been recognised as a genus distinct from Eucalyptus.

See here for a more detailed outline of the groups of eucalypts with a particular reference to those taxa that occur in the Australian Capital Territory.

Habit

  • Eucalyptus
      Eucalyptus exhibits a variety of habits. They can be shrubs (e.g. Eucalyptus vernicosa from western Tasmania grows to about 1m or may sometimes be prostrate), mallees (characterized by having several stems from a common lignotuber) or trees (the tallest is Eucalyptus regnans from Victoria and Tasmania which can grow to about 100m). Most however occur as forest trees of 30-50m height or as woodland trees of 10-25m height.

  • Corymbia

      Corymbia occur mainly as trees although rarely as mallees as well. Mostly they reach heights of 10 - 15 m although some (e.g. C. maculata) may reach heights of almost 40 m in favourable situations.

  • Angophora

      Angophora are mainly trees although A. hispida can sometimes occur as a shrub. Angophora range in height from around 10 - 30 m.

    Lignotuber

    Lignotubers occur in some but not all Eucalyptus species. They also occur in some Corymbia species. Lignotubers are a woody swelling, partly or wholly underground and have been shown to contain a mass of vegetative buds and substantial energy reserves. Species that possess lignotubers are often those tolerant to fire, drought and defoliation. Those species that do not produce lignotubers are usually prolific seed producers and survive such disasters as fire with massive seedling regeneration.

    Bark

  • Eucalyptus
      Bark types roughly fall into two categories. There is the persistent type, the "rough barks" (e.g. stringybarks, boxes, peppermints and ironbarks) or partly or wholly regularly shedding type, the "smooth barks" (e.g. scribbly gums).
  • Corymbia

      Both persistent and shedding bark is present in Corymbia. Most species have bark that sheds in equidimensional plates giving a tessellated appearance. Others may have somewhat scaly, persistent bark or smooth wholly deciduous bark.

  • Angophora

      Angophora may have smooth bark (A. costata only) or rough bark.

    Leaves

    Eucalypts show a remarkable dimorphism between their juvenile leaves and their adult leaves. In the majority of cases, juvenile leaves are opposite whilst the adult leaves are usually disjunct opposite. Oil glands are also usually present. The leaves may sometimes be glaucous (covered in a white wax) which causes the leaf to appear whitish, bluish or blue-grey. Coppice growth usually has the form of the juvenile foliage. Some species rarely produce adult foliage and will flower with juvenile foliage present (e.g. Eucalyptus cinerea).

    Inflorescences

    The unit inflorescence is an umbellaster. These are usually simple and axillary (e.g. Eucalyptus pauciflora), compound and axillary (e.g. E. michaeliana) or compound and terminal (e.g. E. polyanthemos).

    Buds, flowers and fruit

  • Eucalyptus and Corymbia
      The calyx and/or corolla fuse to form an operculum which covers the stamens and style in bud. There may be one or two opercula, depending upon the species. The shape of the calyptra varies considerably between species. The stamens are numerous, usually in several continuous whorls and the anthers can be either versatile or adnate and dehisce by separate or confluent slits or pores. The ovary can be inferior or half-inferior with 2 - 8 (rarely more) loculi. The fruit is a woody hypanthium that encloses the base and sides of the capsule. The valves may be sunken, at rim level or exerted. The disc may be level, ascending or descending. The shape and size of the fruit is also very variable between species.

  • Angophora

      In the case of Angophora the calyx and corolla are free - i.e. they never form a calyptra. The fruit are usually ribbed and the calyx lobes usually persist and project from the rim as "teeth".

    Identification

    The Australian National Botanic Gardens and Centre for Plant Biodiversity Research offers a Plant Enquiry Service and a Public Reference Herbarium for the identification of plant specimens.

    As members of the eucalypt group can sometimes be tricky to identify, any specimen brought in should have at least mature buds, mature fruits, adult leaves, locality information, a description of its habit and a description of the bark (e.g. - bark rough, bark rough on trunk and smooth on branches, bark smooth or bark smooth with a persistent stocking of rough bark).

    References

    Hill, K.D. and Johnson, L.A.S. (1995). Systematic studies in the eucalypts. 7. A revision of the bloodwoods, genus Corymbia (Myrtaceae). Telopea 6(2-3): 185-504.

    Morley, B.D. and Toelken, H.R. (eds). (1983). Flowering Plants in Australia. Rigby Publishers, Adelaide.

    Pryor, L.D. and Johnson, L.A.S. (1971). A Classification of the Eucalypts. The Australian National University, Canberra.

    Other References for the Eucalypts

    Bentham, G. (1867). Flora Australiensis: a Description of the Plants of the Australian Territory. Vol. 3 Myrtaceae to Compositae. 704 pp. Lovell Reeve & Co., London.

    Brooker, M.I.H. and Kleinig, D.A. (1990). Field Guide to Eucalypts. Vol. 1, Revised edition. Inkata Press Proprietary Limited, Melbourne and Sydney.

    Brooker, M.I.H. and Kleinig, D.A. (1990). Field Guide to Eucalypts. Vol. 2. Inkata Press Proprietary Limited, Melbourne and Sydney.

    Brooker, M.I.H. and Kleinig, D.A. (1994). Field Guide to Eucalypts. Vol. 3. Reed International Books Australia Pty Limited trading as Inkata Press.

    Chippendale, G.M. (1988). Eucalyptus. In: Chippendale, G.M. Flora of Australia Vol. 19, Myrtaceae, Eucalyptus, Angophora, Australian Government Publising Service, Canberra.

    Hill, K.D. (1991). Eucalyptus. In: Harden, G.J. (ed). Flora of New South Wales. Vol. 2. University of New South Wales Press, Kensington.

    Johnson, L.A.S. and Briggs, B.G. (1983). Myrtaceae. In Morley, B.D. and Toelken, H.R. (eds). Flowering Plants in Australia. Rigby Publishers, Adelaide.

    Udovicic, F., McFadden, G.I. and Ladiges, P.Y. (1995). Phylogeny of Eucalyptus and Angophora based on 5S rDNA spacer sequence data. Molecular Phylogenetics and Evolution 4(3): 247-256.

    Many thanks to Ian Brooker (ian.brooker@pi.csiro.au)
    for commenting upon a draft of this document.

    Proceed to
    "The Major Groups of Eucalypts -
    The Genera Eucalyptus, Corymbia and Angophora"

  • "Introduction to the Eucalypts" originally posted 27 March 1992.

  • "An Introduction to the Eucalypts - the Genera Eucalyptus, Corymbia and Angophora posted 11 September 1996.

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    An Introduction to the Eucalypts
    Andrew Lyne
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