Flower bud growth, mortality rate, and population structure of Griffith f. Banziger & Hansen (Rafflesiaceae) in a subtropical forest, northeastern India

apria himalayana Griff. f. albovinosa Banziger & Hansen (Rafflesiaceae) is rare and endemic to northeastern Thailand, Vietnam, and Manipur, with a short flowering season ranging from late October to late November, due to which its detailed phenology is poorly understood. To protect this valuable taxon from extinction threats, monitoring the growth of flower buds is crucial. The objectives of this study were to analyse the growth of flower buds at various developmental stages, the mortality rate, and the population structure of Sapria himalayana f. albovinosa. The buds were monitored, vertically photographed, and measurements of the plant buds and flowers were recorded for every observation. The present study resulted in the flower bud growth having six different developmental stages, namely the copule, copule-bract transition, bract, bract-perigone transition (BPT), perigone, and anthesis stage, with a diameter range of 0.3–2.3 cm, 2.4–4.0 cm, 4.1–5.5 cm, 5.6–6.1 cm, 6.2–8.1 cm, and 16–20 cm, respectively. The population was dominated by the copule stage in the initial observation, while it was dominated by the perigone and anthesis stages in the final observation, which indicated that the optimal flowering season was from late October to late November. A total of 58 flower buds were recorded, out of which 24.13% of flower buds were dead without reaching maturity due to fungal infections and were injured due to anthropogenic interventions. Hence, the information on the growth of buds, flower development stages and their mortality rate is vital for taxonomic studies, field monitoring, and conservation purposes.