South America is the center of diversity of the genus Isoetes and several new species have been described in the last decade, especially in Brazil. Isoetes cangae J.B.S. Pereira, Salino & Stützel was first recognized in 2016 as an endemic species of a single lake in Serra dos Carajás, Brazil, in the southeastern Amazon region. The climate of Amazon is warm with a seasonal precipitation regime, which affects aquatic ecosystem properties and regulates plant phenology. Understanding how climatic and hydrological drivers affect I. cangae is fundamental for its conservation because the species is quite vulnerable due to its restricted distribution. In this study, we evaluated the effects of seasonal climatic variations and water level on the phenology of I. cangae over two years. The maximum leaf length, the number of sporophylls (fertile leaves), and the total number of leaves were assessed. Sporophylls were classified into mature and immature, megasporophylls and microsporophylls. The number of leaves, leaf length, and the number of sporophylls changed drastically among the hydrological seasons, but not the ratio between sporophylls and leaves, suggesting that reproductive effort is distributed accordingly over the years. All these factors also varied between years, indicating that inter-annual climatic variations affect the morphology and reproduction of I. cangae. Sporophylls are produced throughout the year, but their maturation and release increase in the rainy and early dry seasons, respectively. Megasporophylls predominate over microsporophylls throughout the year, and the peak of sporophyll maturation occurs during the rainy season, but lasts longer (till early dry season) for megasporophylls. The reproductive traits were associated with lake water level, suggesting that development is stimulated during the driest and hottest periods. Therefore, our results show that environmental factors play an important role in I. cangae phenology and must be considered in the management and conservation efforts to preserve this ancient Amazonian plant.

南美洲是Isoetes属多样性的中心，在过去十年中已经描述了几个新物种，特别是在巴西。Isoetes cangae JBS Pereira, Salino & Stützel 于 2016 年首次被确认为亚马逊东南部巴西 Serra dos Carajás 单个湖泊的特有物种。亚马逊气候温暖，具有季节性降水制度，影响水生生态系统特性并调节植物物候。了解气候和水文驱动因素如何影响I. cangae是其保护的基础，因为该物种因其分布受限而非常脆弱。在这项研究中，我们评估了季节性气候变化和水位对植物物候的影响。I. cangae超过两年。评估最大叶长、孢子叶数（可育叶）和总叶数。孢子叶分为成熟和未成熟、大孢子叶和小孢子叶。叶数、叶长和孢子叶数在水文季节间变化剧烈，但孢子叶与叶的比值变化不大，表明繁殖努力在各年间呈相应分布。所有这些因素在年份之间也有所不同，表明年际气候变化影响了I. cangae的形态和繁殖. 孢子叶全年生产，但它们的成熟和释放分别在雨季和旱季早期增加。大孢子叶一年四季都比小孢子叶占优势，孢子叶成熟的高峰出现在雨季，但大孢子叶持续时间更长（直到旱季初）。繁殖性状与湖水位有关，表明在最干燥和最热的时期会刺激发育。因此，我们的结果表明环境因素在I. cangae物候学中起着重要作用，必须在保护这种古老亚马逊植物的管理和保护工作中加以考虑。