Abstract
BackgroundThe genus Cypripedium L. is one of the five genera of the subfamily Cypripedioideae, members of which are commonly known as lady’s slipper orchids. Cypripedium japonicum is a perennial herb native to East Asia, specifically China, Japan, and Korea. Due to its limited distribution, the species is included in the Endangered category of the IUCN Red List.ResultsWe investigated gametophyte development, including complete embryogenesis, in C. japonicum. The complete reproductive cycle is presented based on our observations. Anther development begins under the soil, and meiosis of pollen mother cells begins 3 weeks before anthesis, possibly during early April. The megaspore mother cells develop just after pollination in early May and mature in mid–late June. The pattern of embryo sac formation is bisporic, and there are six nuclei: three forming the egg apparatus, two polar nuclei, and an antipodal cell in the mature embryo sac. Triple fertilization results in the endosperm nucleus, which degenerates when the proembryo reaches the eight-to-sixteen-cell stage.ConclusionOur overall comparisons of the features of gametophyte and embryo development in C. japonicum suggest that previous reports on the embryology of Cypripedium are not sufficient for characterization of the entire genus. Based on the available information, a reproductive calendar showing the key reproductive events leading to embryo formation has been prepared.
Highlights
The genus Cypripedium L. is one of the five genera of the subfamily Cypripedioideae, members of which are commonly known as lady’s slipper orchids
This study provides a complete overview of the embryology of the endangered slipper orchid C. japonicum
Suetsugu and Fukishima [28] found that the fruit set percentage of C. japonicum by natural pollination was only 14.9%, and the value was even lower in the samples studied by Sun et al [29]
Summary
The genus Cypripedium L. is one of the five genera of the subfamily Cypripedioideae, members of which are commonly known as lady’s slipper orchids. The genus Cypripedium L. is one of the five genera of the subfamily Cypripedioideae, commonly known as lady’s slipper [1, 10]. A unique feature of Cypripedioideae orchids is the one-way trap flower, which offers a fixed and unidirectional route to pollinators (see [15]). Despite this fixed pollination route, slipper orchids exhibit a remarkable degree of diversity in food mimesis traits such as scent, color and flower size for their pollinators [15,16,17,18,19]
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