Pseudoflower formation is arguably the rarest outcome of a plant-fungus interaction. Here we report on a novel putative floral mimicry system in which the pseudoflowers are composed entirely of fungal tissues in contrast to modified leaves documented in previous mimicry systems. Pseudoflowers on two perennial Xyris species (yellow-eyed grass, X. setigera and X. surinamensis) collected from savannas in Guyana were produced by Fusarium xyrophilum, a novel Fusarium species. These pseudoflowers mimic Xyris flowers in gross morphology and are ultraviolet reflective. Axenic cultures of F. xyrophilum produced two pigments that had fluorescence emission maxima in light ranges that trichromatic insects are sensitive to and volatiles known to attract insect pollinators. One of the volatiles emitted by F. xyrophilum cultures (i.e., 2-ethylhexanol) was also detected in the head space of X. laxifolia var. iridifolia flowers, a perennial species native to the New World. Results of microscopic and PCR analyses, combined with examination of gross morphology of the pseudoflowers, provide evidence that the fungus had established a systemic infection in both Xyris species, sterilized them and formed fungal pseudoflowers containing both mating type idiomorphs. Fusarium xyrophilum cultures also produced the auxin indole-3-acetic acid (IAA) and the cytokinin isopentenyl adenosine (iPR). Field observations revealed that pseudoflowers and Xyris flowers were both visited by bees. Together, the results suggest that F. xyrophilum pseudoflowers are a novel floral mimicry system that attracts insect pollinators, via visual and olfactory cues, into vectoring its conidia, which might facilitate outcrossing of this putatively heterothallic fungus and infection of previously uninfected plants.

假花的形成可以说是植物-真菌相互作用的最罕见的结果。在这里，我们报告了一种新的假定花卉模拟系统，其中假花完全由真菌组织组成，与以前的模拟系统中记录的改良叶子形成对比。从圭亚那的稀树草原收集的两种多年生Xyris物种（黄眼草，X. setigera和X. surinamensis）上的假花是由Fusarium xyrophilum（一种新型镰刀菌属）产生的。这些假花在大体形态上模仿Xyris花，并且具有紫外线反射性。F. xyophilum 的无菌培养产生了两种颜料，它们在三原色昆虫敏感的光范围内具有荧光发射最大值，并且已知会吸引昆虫传粉者的挥发物。在X. laxifolia var.的顶部空间中也检测到了一种由F. yyrophilum培养物释放的挥发物（即 2-乙基己醇）。iridifolia花卉，多年生品种，原产于新大陆。显微镜和 PCR 分析的结果，结合对假花大体形态的检查，提供了证据表明该真菌已在两种Xyris物种中建立了全身感染，对它们进行了消毒并形成了含有两种交配型特性的真菌假花。干酪镰刀菌培养物还产生生长素吲哚-3-乙酸 (IAA) 和细胞分裂素异戊烯基腺苷 (iPR)。实地观察表明，假花和Xyris花都被蜜蜂访问过。总之，结果表明F. xyrophilum pseudoflowers 是一种新的花卉模拟系统，它通过视觉和嗅觉线索吸引昆虫传粉者引导其分生孢子，这可能有助于这种假定的异源真菌的异交和感染以前未感染的植物。