L'InfioreSCenZA Nel Genere Eucalyptus E La SUa InterpretaZIone

Abstract

The Inflorescence of EUCALYPTUS and its Interpretation. — The inflorescence in the genus Eucalyptus is apparently quite variable. Therefore, in the floral organisation morphologists have identified four different types: 1) solitary flowers; 2) umbel; 3) panicle; 4) corymb (fig. 1). The inflorescence called umbel may also appear under the following different aspects: a 3-flowered umbel (which is to be considered as a cyme); an umbel with pedicellate flowers; an umbel with sessile flowers (which is therefore a head) (fig. 2). Blake first (1953) thought, that the 3-flowered umbel was a simple dichasium, and he pointed out that the other types of inflorescences were branched and highly modified dichasia (figs. 4–2). This hypothesis has been confirmed and enlarged by Pryor (1954) and Carr & Carr (1959) after a more detailed study of the developmental morphology of the inflorescence and mainly of the characters of bracts (figs. 10–2). Their studies proved that all the inflorescences (umbels, heads, panicles, etc.) are modified dichasia; even the solitary flower is a dichasium reduced to the terminal flower of the main axis (fig. 12). Therefore the dichasium, according to Blake, is the fundamental structure of all the inflorescences of Eucalyptus.

Starting from these researches, the Author reviews the different theories concerning the interpretation of the inflorescences and he tries to apply these theories to the genus Eucalyptus. Rickett's theory (following which the dichasium is the fundamental unit of inflorescences) well explains the above mentioned structures (fig. 13). The other different theories on the evolution of inflorescences (Takhtajan 1959, Zimmermann 1959, etc.) are also evaluated (figs. 14, 15). The various steps of the evolution of the inflorescence in the genus Eucalyptus are described; the gradual process of reduction from the branched dichasium up to the solitary flower is also explained (figs. 16, 17).

At the end of the paper there are also some notes on the morphology of other inflorescences of Myrtaceae and on their interpretation.