Scanning electron microscopy analysis of early floral development in Renanthera bella J. J. Wood, an endemic orchid from Sabah

Renanthera bella J. J. Wood is an endemic orchid to Sabah with beautiful bright red petals. Most of the floral development of orchids is significantly affected by seasons and geographical factors. To date, the flower development stages of R. bella have never been studied. This study was conducted to observe the morphological changes of flower initiation and early development by apical dissection and scanning electron microscopy (SEM). The floral organs were dissected and fixed in 1.5% glutaraldehyde and dehydrated with alcohol. Characteristic stages of the initial flowering pattern were recorded until the flower was fully open and become senescent. Renanthera bella showed a typical acropetal pattern starting with early flowering from the base to the apex, forming a raceme-type inflorescence. Its flower development was divided into ten stages, which started with the flower bud appearance and the initiation of primordia. Next, the flower sepal started to develop within seven days of bud appearance. The final stage occurred after 25 days of observation when the bud opened, with an average bud length and diameter of 1.94 ± 0.56 cm and 0.50 ± 0.29 cm, respectively. The R. bella flower maturity stage was achieved between 38 to 40 days after anthesis, with the average length and diameter of petals and sepals increasing to 2.49 ± 0.23 cm and 0.38 ± 0.06 cm, respectively. A capsule successfully formed after one week of pollination. It reached the maturity stage at approximately 15 weeks after pollination. The orchid capsule started to break and expose the seeds inside after 21 weeks. This analysis emphasized the early floral development pattern, which could help estimate the length of flower maturity and pollination.