Phenology and floral morph variation suggest non-classical distyly in the Sisrè berry plant [Synsepalum dulcificum (Schumach. & Thonn.) Daniell, Sapotaceae]

Understanding floral biology and phenological variation patterns in plant species is crucial for hybridization and genetic improvement. In Synsepalum dulcificum (Sisrè berry plant), the lack of such knowledge hinders proper mastering of the pollination ecology of this species, with drawbacks in terms of cross success. A total of 100 S. dulcificum juveniles from two sites and 250 flowers were selected, monitored for two years, and assessed for phenological phase durations, synchronization pattern, flower abortion and floral morphometrics. Data were analyzed by combining generalized linear models with binomial and Poisson error structures, t-test, Mann-Whitney test and circular statistics. Our results revealed that S. dulcificum is a non-classical distylous species with an isoplethy (equal frequency of floral morphs) marked by all individual plants unexpectedly exhibiting both S- and L- floral morphs. Abortion was as high as 86%, culminated at the phases of style and petal wilting (26%) and fructification onset (28.7%), and varied from year 1 (93.7%) to year 2 (79.8%) (χ2 = 23.63, df = 1, p < 0.001, Cohen’ d effect size = 0.42). The length of the phenological phases varied across (85 days for year 1 vs 86 days for year 2) and within the year (85 days for dry season vs 91 days for rainy season), with an average fruiting cycle of 87 ± 2 days. Flowering and fruiting were highly synchronous across sites with a marked seasonality whose extent was site- and phenophase- specific (Flowering: Rayleigh Z = 0.0534, p = 0.001 for site 1 and Rayleigh Z = 0.2213, p < 0.001 for site 2; Fruiting: Rayleigh Z = 0.4672, p < 0.001 for site 1 and Rayleigh Z = 0.4502, p < 0.001 for site 2). January and April represent peak periods for most of the phenological events in the species. These findings suggest a need to redefine individual-level morph classification in distylous species and explore the biological drivers of high abortion rates in S. dulcificum.