Abstract
The dioecious relic Cercidiphyllum japonicum is one of two species of the sole genus Cercidiphyllum, with a tight inflorescence lacking an apparent perianth structure. In addition, its systematic place has been much debated and, so far researches have mainly focused on its morphology and chloroplast genes. In our investigation, we identified 10 floral organ identity genes, including four A-class, three B-class, two C-class and one D-class. Phylogenetic analyses showed that all ten genes are grouped with Saxifragales plants, which confirmed the phylogenetic place of C. japonicum. Expression patterns of those genes were examined by quantitative reverse transcriptase PCR, with some variations that did not completely coincide with the ABCDE model, suggesting some subfunctionalization. As well, our research supported the idea that thebract actually is perianth according to our morphological and molecular analyses in Cercidiphyllum japonicum.
Highlights
The middle and inner scales are peak green with a rose-red margin and turn yellowish with a red margin when mature
Juvenile leaves with transparent scrotiform glands in the margin are involute when they are wrapped in scales
The inflorescence of C. japonicum is highly simplified, with their pistillate inflorescence formed by four subtranslucent peak green bracts and 2–6 carpels, whose flat and upturned stigma is yellowish-green when young and turn scarlet when mature (Fig 1A)
Summary
Is a tertiary relic plant and only occurs as a species of east Asian flora. Paleontology research shows that it was once widely distributed in the northern hemisphere. It is only sporadically found in China and Japan [1,2]. C. japonicum has considerable presence as a tree with colorful leaves. The tree displays typically colored leaves showing amaranthine in the spring, emerald in the summer, golden in the fall and carmine in the winter. It has great economic value given that its fruits and leaves can be used as medicines and the bark is used for tannic extracts. Its dioecious, achlamydeous and extreme simplification inflorescence makes it an ideal material for the study of sexual differentiation and regulation of floral development
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