Embryological studies on endangered Ophiopogon xylorrhizus (Liliaceae)

The embryological studies on an endangered species Ophiopogon xylorrhizus are reported in this paper. The anther was four-sporangiate, and its wall was composed of four layers: epidermis, fibrous endothelium, middle layer and glandular tapetum. Cytokinesis of microspore mother cell in meiosis was of the Successive type, and tetrads were tetrahedral or isobilateral. The mature pollen grains were 2-celled. Ovules were anatropous, bitegminous, and crassinucellate. Ovary wall ruptured 4～5 days after fertilization. The development of embryo sacs conformed to the Polygonum type. The two polar nuclei fused into a secondary nucleus before fertilization. The embryogeny was of the Asterad type, and endosperm development corresponded to the Nuclear type. About 55.8 % individuals in the population of O. xylorrhizus were found male sterile, and 43.3% of embryos aborted at early development stage. As a conclusion, we consider that (1)the failure of the xenogamy resulted from male sterility, autogamy and inefficient pollination agents, (2)embryo abortion and (3)exposure of young seeds during their early development are the weak links in the sexual reproductionof O. xylorrhizus, which would contribute to the endangerment of this species