PREMISE Floral rewards are essential in understanding floral function and evolution of the relationships between flowers and pollinators. Whether sugars are present in stigmatic exudates in Anthurium and whether it has floral nectaries have remained controversial because of the scarcity of structural studies. To solve these questions, we investigated the floral anatomy of A. andraeanum to elucidate whether (1) tepals are secretory organs, (2) tepals possess a structurally recognizable nectary, and (3) tepalar secretion differs from stigmatic secretion. METHODS Floral structure was assessed through light and electron microscopy of samples of immature, pistillate, and staminate flowers. The dynamics of the starch reserve was investigated using histochemical tests, and the sugar content in the floral exudates was assessed using thin-layer chromatography. RESULTS Sugar analysis did not detect sucrose, glucose, or fructose in stigmatic secretions, but confirmed their presence in tepalar secretions. Stigmatic secretion was produced by secretory stigmatic papillae; tepalar exudates were produced by nonvascularized nectaries in the apex of tepals. These nectaries were characterized by modified stomata and cells with cytoplasm rich in organelles, and a high content of calcium oxalate crystals. CONCLUSIONS Our results showed for the first time nectaries on tepals and true nectar secretion for A. andraeanum. Stigmatic secretion appears to be a distinct substance, and its often-reported sugar content seems to be a result of sample contamination. Nectar and stigmatic secretions have been often mistaken in other Anthurium species and deserve a revision for this genus.

中文翻译：

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真花蜜还是柱头分泌物？结构证据阐明了关于红掌蜜腺的古老争议

前提 花卉奖励对于理解花卉功能和花卉与传粉媒介之间关系的进化至关重要。由于缺乏结构研究，红掌的柱头渗出液中是否存在糖分以及它是否具有花蜜腺一直存在争议。为了解决这些问题，我们研究了 A. andraeanum 的花解剖以阐明是否 (1) 花被片是分泌器官，(2) 花被片具有结构上可识别的蜜腺，以及 (3) 花被分泌物与柱头分泌物不同。方法通过光学和电子显微镜对未成熟花、雌花和雄花样品进行花卉结构评估。使用组织化学测试研究淀粉储备的动态，并且使用薄层色谱法评估花分泌物中的糖含量。结果 糖分析未检测到柱头分泌物中的蔗糖、葡萄糖或果糖，但证实了它们在花萼分泌物中的存在。柱头分泌物由分泌柱头乳头产生；花被分泌物由花被顶端的无血管化的蜜腺产生。这些蜜腺的特征是气孔和细胞质中含有丰富的细胞器，以及高含量的草酸钙晶体。结论 我们的结果首次显示了花被片上的蜜腺和 A. andraeanum 的真正花蜜分泌。柱头分泌物似乎是一种独特的物质，其经常报告的糖含量似乎是样品污染的结果。