Reproductive and vegetative phenology of the micro endemic Stachytarpheta cassiae (Verbenaceae)

Abstract The flora of the Brazilian rupestrian grasslands represents a hotspot of species richness and endemisms. Stachytarpheta cassiae (Verbenaceae), is a micro endemic species, from which nothing is known. Here, we quantified the activity and intensity of vegetative and reproductive phenophases throughout 12 months and tested for their seasonality and their relationship with local climatic variables. Both vegetative and reproductive phenophases were continuous. No seasonality was observed in the vegetative phenophases and none of them was influenced by climatic variables. Only flower buds and mature fruits’ intensities showed seasonality in February (rainy season) and July (dry season), respectively. Accordingly, increased temperature and humidity combined explained increased production of flower buds whereas decreased rainfall explained increased mature fruits. Higher intensity in flower buds may respond to similar climatic conditions as other species in the community. However, S. cassiae is much different as it continues producing flowers continuously. Higher intensity of mature fruits in the dry season is expected as their seeds are abiotically dispersed. Due to constant flower and leaf production, S. cassia may be a key species for the conservation of many vertebrate and invertebrate species and for maintaining the biogeochemical functioning of the impoverished soils of the rupestrian grasslands.

摘要 巴西岩生草原（rupestrian grasslands）的植物区系是物种丰富度与特有性的热点区域。其中，鲜为人知的微特有种Stachytarpheta cassiae（马鞭草科Verbenaceae）尚未有相关研究报道。
本研究对该物种开展为期12个月的跟踪观测，量化其营养生长与生殖生长物候的发生活动与强度，并检验其物候季节性特征及其与当地气候变量的相关性。
观测结果显示，该物种的营养生长与生殖生长物候均呈连续发生特征；营养生长物候未表现出明显季节性，且各阶段均不受气候变量影响。仅花芽与成熟果实的物候强度分别在雨季2月与旱季7月呈现季节性变化。
进一步分析表明，气温与湿度的协同升高可促进花芽生成，而降雨量减少则会促使成熟果实产量提升。花芽物候强度升高的响应模式与群落内其他物种一致，但S. cassiae的独特之处在于其可持续不间断地开花。
旱季成熟果实物候强度升高符合预期，因其种子为非生物传播类型。由于该物种可持续产生叶片与花朵，S. cassiae可能是维系诸多脊椎动物与无脊椎动物物种存续，以及维持岩生草原贫瘠土壤生物地球化学功能的关键物种。