Characters of the inferior ovary of Myrteae (Myrtaceae) and their implication in the evolutionary history of the tribe

Abstract

Myrtaceae is commonly known to have an inferior ovary of appendicular, receptacular or mixed origin. Other characters of the ovary, such as the number of carpels, number of locules, vascularisation pattern, number of ovules, placentation and presence of compitum have also been of interest to researchers aiming to better understand the evolutionary history of the tribe. In the present study, aspects of the structure of the inferior ovary of 21 species of Myrteae are analysed and reviewed as potential characters for better understanding the evolutionary history of Myrteae. Flower buds were embedded in historesin and paraplast and sectioned transversely and longitudinally with a rotary microtome. Results suggested that most species have an inferior ovary of appendicular origin and that a compitum, or compitum tissue, is present in all species analysed, differing only in the degree of development. Number of carpels and locules vary, with most species having two locules. Vascular supply is transeptal and axial, the latter being the most common condition in the investigated species. Data presented here enhance current evolutionary understanding of the tribe and its history. Results indicated that the inferior ovary of ancestral Myrteae may has had an appendicular origin, that the presence and nature of the compitum may have a positive effect on fertilisation efficiency and a relationship with number of ovules and that transepetal vascular supply may be taxonomically useful to define large groups such as Pimenta and Eugenia.