The evolution of full mycoheterotrophy in orchids likely occurs through intermediate stages (i.e., partial mycoheterotrophy or mixotrophy), in which adult plants obtain nutrition through both autotrophy and mycoheterotrophy. However, because of its cryptic manifestation, partial mycoheterotrophy has only been confirmed in slightly more than 20 orchid species. Here, we hypothesized that Oreorchis indica is partially mycoheterotrophic, since (i) Oreorchis is closely related to leafless Corallorhiza, and (ii) it possesses clustered, multi-branched rhizomes that are often found in fully mycoheterotrophic orchids. Accordingly, we investigated the nutritional modes of O. indica in a Japanese subboreal forest by measuring the ¹³C and ¹⁵N abundances and by community profiling of its mycorrhizal fungi. We found that O. indica mycorrhizal samples (all 12 samples from four individuals) were predominantly colonized by a single OTU of the obligate ectomycorrhizal Tomentella (Thelephoraceae). In addition, the leaves of O. indica were highly enriched in both ¹³C and ¹⁵N compared with those of co-occurring autotrophic plants. It was estimated that O. indica obtained 44.4 ± 6.2% of its carbon from fungal sources. These results strongly suggest that in the Oreorchis-Corallorhiza clade, full mycoheterotrophy evolved after the establishment of partial mycoheterotrophy, rather than through direct shifts from autotrophy.

兰花中完全真菌异养的进化可能发生在中间阶段（即部分真菌异养或混养），成年植物通过自养和真菌异养获得营养。然而，由于其隐秘的表现，仅在略多于20种的兰花物种中证实了部分真菌异养。在这里，我们假设唇兰属籼是部分mycoheterotrophic，因为（我）唇兰属密切相关，光秃秃的珊瑚兰属，及（ii）其拥有集群，这往往是在完全mycoheterotrophic兰花发现多支根茎。因此，我们通过测量日本亚热带森林中的印度。稻的营养模式¹³ C和¹⁵ N丰度以及其菌根真菌的分布图。我们发现，印度。菌的菌根样品（来自四个人的所有12个样品）主要被一个专一的外生菌根毛囊藻（Thelephoraceae）的单个OTU定殖。此外，与自生植物同时存在的印度O稻叶片在¹³ C和¹⁵ N中均高度富集。据估计，印度O稻从真菌来源获得其碳的44.4±6.2％。这些结果强烈表明，在Oreorchis-Corallorhiza 进化枝，完全的真菌异养症是在部分性真菌异养症建立后进化而来的，而不是通过自体养分的直接转变而形成的。