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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).
References
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