J Syst Evol

• Research Articles •    

Floral morphogenesis of the Maddenia and Pygeum groups of Prunus (Rosaceae), with an emphasis on the perianth

Xi Wang1,2†, Jun‐Ru Wang1,2†, Si‐Yu Xie1,2, Xiao‐Hui Zhang3, Zhao‐Yang Chang1,2, Liang Zhao1,2*, Louis Ronse De Craene4, and Jun Wen5   

  1. 1 College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China
    2 Herbarium of Northwest A&F University, Yangling, Shaanxi 712100, China
    3 College of Life Sciences, Shaanxi Normal University, Xi'an, Shaanxi 710119, China
    4 Royal Botanic Garden Edinburgh, Edinburgh EH3 5LR, UK
    5 Department of Botany, National Museum of Natural History, MRC 166, Smithsonian Institution, Washington, DC 20013‐7012, USA
  • Received:2020-12-29 Accepted:2021-03-30 Online:2021-04-03

Abstract: Although the vast majority of Prunus L. (Rosaceae) species have clearly differentiated sepals and petals, two former genera Maddenia and Pygeum have been described as having an undifferentiated perianth. However, floral morphological and morphogenetic data are scarce, and a renewed investigation is essential to understand the evolution of the perianth differentiation. Here, floral morphogenesis in Prunus hypoleuca (Koehne) J.Wen (=Maddenia hypoleuca Koehne) and Prunus topengii (Merr.) J. Wen & L. Zhao (=Pygeum topengii Merr.) were examined with scanning electron microscopy. The floral development demonstrates that the ten perianth parts can be distinguished as five sepals in an external whorl and five petals in an internal whorl. The sepal primordia are broad, crescent-shaped, and truncate. The petal primordia are rounded and initially resemble the androecium. However, at maturity petals and sepals look much the same in the two species, differing from other Prunus species. The ovule is anatropous and unitegmic, but there is a basal appendage near the ovule of P. hypoleuca which is absent in P. topengii. The direction of development of floral nectaries in the hypanthium is basipetal in P. hypoleuca but acropetal in P. topengii. Perianth segments are differentiated in the two groups and the similarity of the perianth parts is secondarily acquired. Our results support the separation of the Maddenia and Pygeum groups as well as their inclusion in a broader monophyletic Prunus based on molecular phylogenetic studies. We herein provide a new nomenclatural change: Prunus topengii (Merr.) J. Wen & L. Zhao, comb. nov.

Key words: floral development, floral morphology, perianth differentiation, petals, Prunus, Rosaceae