Homogeneous colleters in Myrteae (Myrtaceae)

Colleters are secretory structures characteristic of the apices of more than 60 botanical families. In the Myrtaceae, three types of colleters were previously described: petaloid, conical, and euriform. In Argentina, most species of the Myrtaceae family grow in subtropical regions and a few in the temperate-cold zones of Patagonia. We evaluated the vegetative buds of five species of the subfamily Myrtoideae, tribe Myrtea: Amomyrtus luma, Luma apiculata, and Myrceugenia exsucca, native to the temperate rainforests of Patagonia and Myrcianthes pungens and Eugenia moraviana from the riparian forest of northwestern Corrientes, in order to analyze the presence and morphological types and main secretion products of colleters. Optical and scanning electron microscopy was used to identify the presence of colleters in vegetative organs. Histochemical tests were performed to identify the main secretion products in these structures. The colleters are on the inner side of the leaf primordia and cataphylls and on the edge of the petiole, where they replace the stipules. They are classified as homogeneous because they consist of epidermis and internal parenchyma, both formed by cells with similar characteristics. They lack vascularization and originate from the protodermis. The colleters are of the conical type in L. apiculata, M. pungens, and E. moraviana and of the euriform type in A. luma and M. exsucca, the latter being identified by its dorsiventrally flattened shape. Histochemical tests showed the presence of lipids, mucilage, phenolic compounds, and proteins. This is the first time that colleters have been described in the analyzed species; the taxonomical and phylogenetic importance of this structures is discussed in relation to the Myrtaceae family.