Leaf Venation in Eucalyptus and Other Genera of Myrtaceae: Implications for Systems of Classification of Venation

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Abstract
Two types of venation in leaves of eucalypts and other members of Myrtaceae are described and their ontogeny investigated in species of Eucalyptus. Primary seedling leaves of eucalypts have brochidodromous venation. A paramarginal vein is formed from the extensions of primary lateral veins and completed by the strengthening of commissural minor veins. Adult Eucalyptus leaves have intramarginal veins that are formed independently of the primary laterals which join them after their formation. The apparently brochidodromous venation of leaves of some species arises as a result of differential growth following the inception of intramarginal veins. Leaves with intramarginal veins are ontogenetically acrodromous. These conclusions are discussed in relation to the system of classification of venation put forward by L. J. Hickey. In particular, problems of ordination, affecting the terminology of veins, and of homology arising from the application of the rules of that system to the Myrtaceae, are dealt with.