Data from: Inflorescence and flower development in Musa velutina H. Wendl. & Drude (Musaceae), with a consideration of developmental variability, restricted phyllotactic direction, and hand initiation

Premise of research. Inflorescence and flower structure in the Musaceae is unique in the Zingiberales. The inflorescence lacks the obvious cincinnus structure that characterizes the order, and the flowers are unisexual. Previous studies were conducted using cultivated varieties and were carried out with sectioned material, which does not permit accurate developmental descriptions. Developmental study of a wild species with modern methods addresses these shortcomings and provides more accurate descriptions. Methodology. Young inflorescences and flowers were collected from botanical gardens in Hawaii and Australia and critical-point dried for observation with a scanning electron microscope. Pivotal results. All shoots and inflorescences have sinistrorse (left-handed) phyllotaxy, and the sequence of flower initiation is usually correlated with this pattern. Initiation begins on the cathodic side of the hand (opposite the direction of phyllotactic rise) and progresses anodically (in the direction of phyllotactic rise). Within this general pattern, the sequence of flower initiation is variable, even within the same inflorescence. Five patterns of initiation are reported, with additional variation within each pattern. Both male and female flowers have similar early developmental patterns but diverge at the time of petal/inner androecial formation. In male flowers the anterior side of the flower develops slightly ahead of the posterior, while in female flowers the posterior side develops slightly ahead of the anterior. While consistently present in the material analyzed here, these differences are not apparent at the time of gynoecial initiation or in the mature flowers. Conclusions. The banana inflorescence is another example of how higher-level phyllotactic patterns can influence the sequence of organ initiation at lower levels. Despite variability in the sequence of flower initiation in a hand, the best interpretation of the hand remains a cincinnus. Variability in inflorescence and floral development is rarely reported and may be more common than currently supposed.

研究背景。芭蕉科（Musaceae）的花序与花结构在姜目（Zingiberales）中独具特色：其花序不具备该目类群标志性的明显蝎尾聚伞花序（cincinnus）结构，且花为单性花。既往研究多采用栽培品种及切片材料开展，此类材料无法实现精准的发育形态描述。本研究通过现代实验方法对野生种进行发育学研究，弥补了上述不足，可获得更为精准的发育形态描述。
研究方法。从夏威夷与澳大利亚的植物园采集幼嫩花序及花材，经临界点干燥法处理后，利用扫描电子显微镜（Scanning Electron Microscope, SEM）进行观察。
关键结果。所有茎枝与花序均为左旋（sinistrorse）叶序，花器官起始顺序通常与该叶序模式相关联：起始始于“果手”（花序的分枝单位）的阴极侧（与叶序上升方向相反），并向阳侧（与叶序上升方向一致）推进。即便在同一花序内，花器官起始顺序也存在变异；本研究共报道5种花器官起始模式，且每种模式内部均存在额外变异。雌雄花的早期发育模式相似，但在花瓣/内层雄蕊原基形成阶段出现分化：雄花的花部前侧发育略早于后侧，而雌花的花部后侧发育略早于前侧。尽管该差异在本研究分析的材料中始终存在，但在雌蕊原基起始阶段或成熟花中均无法观察到。
研究结论。香蕉花序是高阶叶序模式可影响低阶花器官起始顺序的又一例证。尽管单个“果手”内的花器官起始顺序存在变异，但其本质仍应被归为蝎尾聚伞花序（cincinnus）。花序与花部发育的变异鲜有报道，但其实际发生率可能远超当前认知。