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

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.

On the Species Delimitation of the Maddenia Group of Prunus (Rosaceae): Evidence From Plastome and Nuclear Sequences and Morphology

“…This provided strong support for the monophyly of Maddenia but it was resolved as nested within Prunus; these conclusions have also been supported by subsequent studies (Chin et al, 2014;Zhao et al, 2016Zhao et al, , 2018Wang et al, 2021). The Maddenia group of Prunus is characterized by its simple deciduous leaves with a serrate margin, terminal racemose inflorescences, 10 undifferentiated perianth parts at maturity, and drupe fruits (Figure 1; Focke, 1894;Yü et al, 1986;Lu et al, 2003;Kalkman, 2004;Wang et al, 2021). The group includes about 4-7 species endemic to East Asia, mainly distributed in the temperate regions of the Himalayas and eastern China, with China as its center of diversity, and one species in Bhutan, Nepal, and Sikkim of India (Rehder, 1956;Yü et al, 1986;Lu et al, 2003;Chin et al, 2010;Wen and Shi, 2012).…”

“…f. & Thoms was established as a genus by Hooker and Thomson (1854) and was later merged with Prunus by Chin et al (2010) based on the phylogenetic analyses of nuclear and plastid DNA sequences. This provided strong support for the monophyly of Maddenia but it was resolved as nested within Prunus; these conclusions have also been supported by subsequent studies (Chin et al, 2014;Zhao et al, 2016Zhao et al, , 2018Wang et al, 2021). The Maddenia group of Prunus is characterized by its simple deciduous leaves with a serrate margin, terminal racemose inflorescences, 10 undifferentiated perianth parts at maturity, and drupe fruits (Figure 1; Focke, 1894;Yü et al, 1986;Lu et al, 2003;Kalkman, 2004;Wang et al, 2021).…”