Research on reproductive phenology, pollination, and embryonic development of Thuja sutchuenensis Franch., a plant species with extremely small populations

We observed and recorded the reproductive phenology, pollination mechanism, and embryonic development of an endangered plant species (Thuja sutchuenensis Franch.). Results showed that: T. sutchuenensis began to differentiate the pistillate strobilus and staminate strobilus in August and pollinated in March of the following year. The pollination mechanism was non-saccate pollen sink into the pollination drop, which was exuded from upright ovules. Its cones became mature for dehisce in October. As seen from microscopic observations, after pollen entered the micropyle, it was stored at the pollen chamber above the nucellus. Some cells in the nucellus differentiated into sporogonia and entered the female gametophyte development stage. In mid-May, pollen was germinated, with fertilization accomplished in early June, after which time the embryo began to develop, finally maturing in early October. Our research also showed that abortion existed throughout the development process from the formation of the pistillate strobilus and staminate strobilus to seed maturation. The major reasons for reproductive failure were ovule abortion and abortion from the megagametophyte during the free nucleus to young embryo stages. This study provides essential information on the reproductive biology of T. sutchuenensis, thus providing a basis for its artificial breeding and formulation of protection strategies.