Micromorphological characterization and electron microscopic study of parasitic species of the family Loranthaceae Juss.

The Loranthaceae Juss. family includes parasitic species that invade important trees such as fruit trees. In Saudi Arabia, Loranthaceae comprises four genera, which include six species that grow in the western, southwestern, and northern regions: Tapinanthus globifer (A.Rich.) Tiegh, Oncocalyx glabratus (Engl.) M. G. Gilbert, Loranthella deflersii (Tiegh.) S. Blanco & C. E. Wetze, Phragmanthera austroarabica A. G. Mill. & J. Nyberg, Plicosepalus curviflorus (Benth.ex Oliv.) Tiegh. and Plicosepalus acaciae (Zucc.). The species present in the Kingdom of Saudi Arabia have not been the subject of enough studies. This work aims to screen and evaluate the taxonomic importance of the micromorphological traits of leaves and fruits in Loranthaceae species native to Saudi Arabia (SA) using scanning electron microscope (SEM). In this study, cluster dendrogram (CD), principal component analysis (PCA) and analysis of variance (ANOVA) were used to evaluate the ability to discriminate Loranthaceae species using micromorphological characteristics. Most of the micromorphological characteristics of the leaf and fruit surfaces used reflected significant variation between the species of Loranthaceae. The type of stomata, trichome, lenticels, fine relief of the cell wall and wax form were the most taxonomically important characteristics. In addition, the cluster dendrogram of morphological characteristics showed species distribution within branches based on affiliation to subtribes Tapinanthinae and Emelianthinae. To the best of our knowledge, the fruit and leaves of the species under study have never been described using electron microscopy, and this study is considered the first of its kind. It also contributes to solving the classification problems of the family Loranthaceae in general and confirms the importance of the characteristics and methods used as tools for characterizing parasitic species that infect trees and helps to verify their identities. This will help to improve resistance efforts and put effective control plans in place.