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The History of Eucalyptus

Although eucalypts must have been seen by the very early European explorers and collectors, no botanical collections of them are known to have been made until 1770 when Joseph Banks and Daniel Solander arrived at Botany Bay with James Cook. There they collected specimens of E. gummifera and later, near the Endeavour River in northern Queensland, they collected E. platyphylla; neither of these species was named as such at the time.

In 1777, on Cook's third expedition, the botanist David Nelson collected a eucalypt on Bruny Island, southern Tasmania. This specimen was taken to the British Museum in London, where it was named Eucalyptus obliqua by the French botanist, Charles-Louis L'Héritier, who was working in London at the time. He coined the generic name from the Greek roots eu and calyptos, meaning 'well' and 'covered', in reference to the operculum of the flower bud. This organ protects the reproductive structures during their development and sheds under pressure from the emerging stamens at flowering. The name obliqua was derived from the Latin, obliquus, meaning 'oblique', describing a leaf base where the two sides of the leaf blade are of unequal length and do not meet the petiole at the same place.

In the publication of Eucalyptus obliqua, L'Héritier perpetuated in the generic name a feature common to all eucalypts - the operculum. In his choice of specific name, he recognised not only a characteristic feature of E. obliqua but one that occurs in most others as well. E. obliqua was published in 1788 and coincides with the date of the first official settlement of Australia.

Between 1788 and the beginning of the nineteenth century several more species of Eucalyptus were named and published. Most of these were by the English botanist James Edward Smith and most were, as might be expected, trees of the Sydney region. They include the economically valuable E. pilularis, E. saligna and E. tereticornis, each of which also occur in Queensland, with the distribution of E. tereticornis extending to eastern New Guinea.

The nineteenth century was a period of extensive land exploration. This resulted in the discovery of many new eucalypts and their subsequent naming by several of the great botanists in Australian history, particularly Ferdinand von Mueller, whose work on eucalypts contributed greatly to the first comprehensive account of the genus in George Bentham's Flora Australiensis (1867) - still the only complete Australian flora. Bentham never visited Australia, but his account is the most important early systematic treatment of the genus Eucalyptus.

Some earlier authors had constructed classifications, but the distinctions they used - for example, shape of the operculum and the juvenile leaf arrangement - were only applicable to far fewer species than were known to Bentham; they were of little use when applied to a much larger number of species. One useful study before that of Bentham, however, was Mueller's description of different bark types (Mueller, 1858). These still have relevance in distinguishing between, for example, groups that shed or retain dead bark and, in the latter case, between ironbark and other types of rough bark.

Bentham divided the genus into five series whose distinctions were based on characteristics of the stamens, particularly the anthers. Categories within each series were based largely on the leaves, and on bud and fruit shape. He was obviously working with limited botanical specimens, and field characters were not available to him unless communicated by others from Australia.

Mueller, working in Australia, devised another classification based on the anthers (Mueller, 1879-84), while Joseph Henry Maiden (1924) elaborated on the anther system, which was taken even further by William Faris Blakely (1934). By this time, classification based on the anther system had become too complex to be workable.

Other more consistent characters have been sought in recent years to aid in the construction of classifications. Of these, leaf venation, the morphology of the seeds, nature of the operculum and the structure of the inflorescence are fundamental. More sophisticated equipment has usually enabled the examination of these leaf and floral structures early in and during their development. Similarities thus recognised usually provide the evidence of natural affinity between species and groups of species. In other words, botanists became better equipped to decide whether these similarities noticed in different species and groups were the results of inheritance from a common ancestor or if they had independently evolved, in many cases as an adaptive necessity such as lignotuber formation or salt tolerance.

A comprehensive but informal classification of all known eucalypt species was published in 1971 by the late L.D. Pryor and L.A.S. Johnson. It comprised seven major groups based on the association of many morphological characters and confirmed by the breeding incompatibility between them. Their system has been subjected to close scrutiny in the past 30 years. Many improvements to this classification were proposed by Johnson himself and by others, although no formal system has been published to accommodate this work.

Briggs and Johnson (1979) contributed a major advance in the botany of the whole family Myrtaceae, in which they outlined for the first time a comprehensive analysis of inflorescence structure in all genera and its indication of evolutionary trend.

In Volume 19 of the "Flora of Australia", all eucalypts published to 1988, were comprehensively treated (Chippendale, 1988). This work includes 513 species of Eucalyptus arranged in 92 series, many of which were published formally in this volume. This is not a structured classification as there are no subgenera or sections. The work is of particular value for its typology and erection of many new taxonomic series.

The past ten years have seen the application of advanced methodology in the study of the genus Eucalyptus, especially in cladistic analyses of taxonomic series (e.g. Ladiges et al., 1987; Hill and Johnson, 1995) and in the use of molecular techniques in the estimation of infra-generic relationships within the genus and between cognate genera (Ladiges et al., 1995; Ladiges and Udovicic, 2000).

In 2000, the senior author of EUCLID, published a formal classification of the genus, which is a synthesis in the form of an updated taxonomy to accommodate the numerous taxa published since Chippendale's 1988 treatment. While based conceptually on the work of Pryor & Johnson, it recognizes 13 subgenera and assigns all species known to the year 2000 to a heirarchical system of subgenera, sections, subsections, series, subseries and supraspecies (Brooker 2000).