Sunlight filtered by green plant tissue becomes diminished in its ratio of red to far‐red wavelengths (R:FR). Some parasitic plants exploit this change by growing towards regions of low R:FR to locate host plants. In principle, variation in R:FR can also convey ecologically relevant information about host proximity or architecture. Here, we demonstrate that the parasitic vine Cuscuta epilinum Weihe (Convolvulaceae) can distinguish fine‐scale differences in R:FR associated with differences in the proximity and shape of potential host plants. We conducted dual‐choice experiments by placing parasite seedlings between targets, including low R:FR fields manipulated via LED lighting and pairs of model plants exhibiting realistic R and FR reflectance but differing in proximity or shape. Seedlings consistently distinguished between low‐R:FR fields of differing intensity. Furthermore, they exhibited preferences for nearer plant models versus identical models placed 4 cm further away and between same‐sized models exhibiting shape differences. Our results indicate that parasites can discriminate minute differences in R:FR signatures corresponding to host factors (proximity and shape) that impact seedling survival. This keen sensory ability underpins the parasite's sophisticated foraging behaviour and highlights the broader importance of light cues in plant ecology.

中文翻译：

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植物寄生虫使用光线索来检测宿主植物接近度和结构的差异

被绿色植物组织过滤的阳光在红光与远红光波长的比率 (R:FR) 中变小。一些寄生植物通过向低 R:FR 区域生长来利用这种变化来定位寄主植物。原则上，R:FR 的变化也可以传达有关宿主接近度或架构的生态相关信息。在这里，我们证明了寄生藤蔓Cuscuta epilinumWeihe（旋花科）可以区分与潜在宿主植物的接近度和形状的差异相关的 R:FR 的精细尺度差异。我们通过在目标之间放置寄生虫幼苗进行了双重选择实验，包括通过 LED 照明操纵的低 R:FR 场和表现出逼真的 R 和 FR 反射率但在接近度或形状上不同的模型植物对。幼苗始终区分不同强度的低 R:FR 场。此外，他们表现出对更近的植物模型的偏好，而不是放置 4 厘米远的相同模型，以及在表现出形状差异的相同大小模型之间。我们的结果表明，寄生虫可以区分与影响幼苗存活的宿主因素（接近度和形状）相对应的 R:FR 特征的微小差异。