The seed development of a mycoheterotrophic orchid, Cyrtosia javanica Blume

Cyrtosia javanica is a rare, mycoheterotrophic vanilloid orchid native to the bamboo forest in central Taiwan. Like some vanilloid orchids, the seeds of C. javanica are hard and difficult to germinate in vitro. A better understanding of the embryology would provide insights in the propagation and conservation of this rare species.

Based on the histological and histochemical studies, we observed some remarkable features in developing seeds of C. javanica. First, the developing embryos without a structurally defined suspensor; Second, the chalazal accessory cells have densely stained cytoplasms that are different from the adjacent cells of seed coat; Third, the multiple layers of seed coat with the lignified in the outermost cell layer of the outer seed coat.

In C. javanica, the large and heavy seeds embedded in fresh fruits may adapt to the dispersal strategy. The hard seeds with lignified outer seed coat could provide a rigid protection during seed dispersal but also cause coat-imposed dormancy. This study provides insights in the seed coat structure and the hints of seed treatment methods.