BACKGROUND AND AIMS Hybanthus austrocaledonicus (Violaceae) is a Ni hyperaccumulator endemic to New Caledonia. One of the specimens stored at the local herbarium had a strip of bark with a remarkably green phloem tissue attached to the sheet containing over 4 Wt% Ni. This study aimed to collect field samples from the original H. austrocaledonicus locality to confirm the nature of the green "nickel-rich phloem" in this taxon and to systematically assess the occurrence of Ni hyperaccumulation in Hybanthus austrocaledonicus and H. caledonicus populations. METHODS X-ray fluorescence spectroscopy (XRF) scanning of all collections of the genus Hybanthus (236 specimens) was undertaken at the Herbarium of New Caledonia to reveal incidences of nickel accumulation in populations of Hybanthus austrocaledonicus and H. caledonicus. In parallel, micro-analytical investigations were performed via Synchrotron X-ray fluorescence microscopy (XFM) and Scanning electron microscopy with X-ray microanalysis (SEM-EDS). KEY RESULTS The extensive scanning demonstrated that Ni hyperaccumulation is not a characteristic common to all populations in the endemic Hybanthus species. Synchrotron X-ray fluorescence microscopy (XFM) revealed that nickel was exclusively concentrated in the epidermal cells of the leaf blade and petiole, conforming with the majority of (tropical) Ni hyperaccumulator plants studied to date. Scanning electron microscopy with X-ray microanalysis (SEM-EDS) of freeze-dried and frozen-hydrated samples revealed the presence of dense solid deposits in the phloem bundles that contained >8 Wt% nickel. CONCLUSIONS The occurrence of extremely nickel-rich green-coloured phloem tissues appears to be a characteristic feature of tropical nickel hyperaccumulator plants.

中文翻译：

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New Caledonian Hybanthus (Violaceae) 中镍的超富集和 Hybanthus austrocaledonicus 中富镍韧皮部的出现

背景和目的 Hybanthus austrocaledonicus (Violaceae) 是新喀里多尼亚特有的镍超富集植物。保存在当地植物标本馆的其中一个标本有一条树皮条，上面有明显绿色的韧皮部组织，附着在含有超过 4 Wt% Ni 的薄片上。本研究旨在从原始 H. austrocaledonicus 地区收集野外样本，以确认该分类群中绿色“富镍韧皮部”的性质，并系统评估 Hybanthus austrocaledonicus 和 H. caledonicus 种群中 Ni 超积累的发生。方法 在新喀里多尼亚植物标本馆对 Hybanthus austrocaledonicus 和 H. caledonicus 种群进行了 X 射线荧光光谱 (XRF) 扫描（236 个标本），以揭示镍积累的发生率。在平行下，通过同步加速器 X 射线荧光显微镜 (XFM) 和具有 X 射线微量分析的扫描电子显微镜 (SEM-EDS) 进行微量分析研究。主要结果 广泛的扫描表明 Ni 超积累不是地方性 Hybanthus 物种所有种群的共同特征。同步加速器 X 射线荧光显微镜 (XFM) 显示，镍仅集中在叶片和叶柄的表皮细胞中，这与迄今为止研究的大多数（热带）镍超富集植物一致。冷冻干燥和冷冻水合样品的 X 射线微量分析 (SEM-EDS) 扫描电子显微镜显示，韧皮部束中存在致密的固体沉积物，其中含有 >8 Wt% 的镍。