Although most orchid species produce minute, light seeds with a one-layer thin seed coat, some in the subfamily Vanilloideae show seed coat with sclerotization and wing development. We investigated the processes of their development by analyzing the anatomy of ovules of two species in the Vanilloideae, Cyrtosia septentrionalis (Rchb. f.) Garay and Erythrorchis altissima (Blume) Blume, that produce seeds with, respectively, rudimentary and well-developed wings. In both species, lignified dark material accumulated in the cells of the outermost layer of the outer integument, forming a sclerotic seed coat. Accumulation started from the cell walls of the outer periclinal surface. C. septentrionalis formed a large embryo and a rudimentary wing and E. altissima formed a small embryo and a well-developed wing. Fully developed seeds of C. septentrionalis and E. altissima were dispersed by animal and wing, respectively. In C. septentrionalis, vascular-bundle-like cells extended from the tip of the funiculus to the chalaza. In E. altissima, they branched into two parts: one reached the chalaza and the other reached a group of cells adjacent to the embryo sac in the micropylar region. The group of cells structurally and functionally resembled hypostase, although hypostase is reported to be present in the chalazal region. A helical vessel was found in one ovule in E. altissima. These observations indicate that the specialized cells represent degenerated vascular bundle cells.
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