Gametophytes and embryo ontogeny: understanding the reproductive calendar ofCypripedium japonicumThunb. (Cypripedoideae, Orchidaceae)

Abstract

AbstractAmong the flowering plants, the gametophyte development and reproductive biology of orchids is particularly poorly understood.Cypripedium japonicumis a perennial herb, native to East Asia. Due to its limited distribution, the species is included in the Endangered category of the IUCN Red List. Light microscopy and SEM methods were used to study the development of the gametes and embryo. The complete reproductive cycle was developed based on our observations. Anther development begins under the soil and meiosis of pollen 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. Triple fertilization results in the endosperm nucleus. A globular embryo is formed after multiple cell division and 9 weeks after pollination the entire embryo sac is occupied by embryo. Overall comparisons of the features of gametophyte and embryo development inC. japonicumsuggest that previous reports on the embryology ofCypripediumare not sufficient to characterize the entire genus. Based on the available information a reproductive calendar showing the key reproductive events leading to embryo formation has been prepared.HighlightManual pollination, reproductive biology and seed development process inCypripedium japonicumThunb., a lady’s slipper orchid endemic to East Asia