Floral organogenesis of Prunus laurocerasus and P. serotina and its significance for the systematics of the genus and androecium diversity in Rosaceae

Abstract

Phylogenetic studies have shown that most clades in Prunus are well-supported by the flower structure, but most taxa in the racemose group have not yet been re-evaluated and could contribute to the understanding of the systematic relationships of the subgenera. We examined the inflorescence and flower development in Prunus laurocerasus L. (subgenus Laurocerasus) and P. serotina Ehrh. (subgenus Padus I) using scanning electron microscopy. Our results indicate that they share several floral development characters but differ in the following aspects: (i) all of their flowers are fully developed and each flower is enclosed by a bract and two bracteoles, which later stop development (vs. the terminal flower degenerates and only a single bract subtends each flower); (ii) the style protrudes from the floral bud (vs. the style is crooked and below the anthers); (iii) the outer integument initiates close to the inner one (vs. in the middle of the ovule); and (iv) an obturator appears after initiation of the two integuments (vs. simultaneously with the inner integument). Although our results are preliminary, differences in floral developmental characters support the different origins of Prunus subgenera Laurocerasus and Padus as based on molecular phylogenetic studies.