Photo credit: www.popsci.com
A fascinating shift in feeding strategies has been observed among certain orchid species, with some abandoning photosynthesis to instead draw nutrients from fungi found in their roots. This parasitic behavior raises intriguing questions about whether the transition is driven by necessity or if these orchids benefit more from their new dietary approach. Recent research focusing on the orchid Oreorchis patens suggests that the change might stem from opportunity rather than a dire need. These findings are published in a study in The Plant Journal on February 19.
Typically, orchids engage in a mutualistic relationship with fungi, where they provide sugars produced through photosynthesis in exchange for essential water and minerals. However, some species have evolved away from this mutualism to solely feed off the fungi, leading to a unique evolutionary adaptation.
Kenji Suetsugu, a co-author of the study and a botanist at Kobe University in Japan, expressed his curiosity about this phenomenon: “I’ve always been intrigued by how orchids turn parasitic. Why would a plant forgo photosynthesis to ‘steal’ resources from fungi?”
In the study, Suetsugu and his team investigated Oreorchis patens, which flourishes in eastern Asia and is recognized for its iridescent yellow flowers. Classified as a partial parasite, this orchid is capable of producing its own sustenance, yet it also absorbs nearly half of its required nutrients from fungal partners. Notably, this species can sometimes exhibit unusual coral-shaped rootstalks, a characteristic more commonly associated with orchids that are entirely dependent on fungi.
Suetsugu aimed to contrast the nutrient acquisition of orchids with coral-shaped root stalks against those with standard roots to assess whether such adaptations correlate with heightened growth or reproductive success.
Plants featuring coral-shaped root stalks (left) alongside their normal-root counterparts (right). CREDIT: Suetsugu et al. 2025.
Conducting fieldwork from June 2010 to November 2021 in three temperate forests, the research team examined over 100 mature Oreorchis patens specimens. They predominantly found these plants in proximity to decaying logs on the forest floor or beneath leaf litter. Remarkably, when these orchids grow near rotting wood, they tend to adjust their fungal symbionts to those that decompose wood, significantly enhancing their nutrient uptake from the decayed matter, all while maintaining their photosynthetic capabilities. Such conditions lead to larger plants that produce more flowers.
“In summary, these orchids are not merely compensating for low photosynthesis; instead, they are amplifying their overall nutrient intake,” stated Suetsugu. This discovery offers a compelling ecological rationale for why a photosynthesizing plant might opt for parasitism.
[ Related: These parasitic plants force their victims to make them dinner. ]
Nevertheless, the reason that fewer than 10 percent of these orchids display this parasitic behavior remains unclear. Transitioning to a parasitic mode requires a switch from their typical fungi to those that can support greater nutrient absorption, which only occur in specific environments like decomposing wood. Therefore, orchids can only adapt to parasitism when they are in proximity to the right decomposition resources, thus limiting the frequency and duration of such opportunistic behavior.
Future investigations could help illuminate the triggers that lead orchids to develop these specialized root structures and explore how environmental conditions may affect their nutrient acquisition from fungi.
“This research is part of an ongoing effort to explore the spectrum from photosynthesis to ultimate parasitism,” Suetsugu concluded. “Ultimately, I hope these findings will enhance our understanding of the diverse strategies that orchids employ to navigate their ecological niches, contributing to the conservation of their remarkable diversity in forest ecosystems.”
Source
www.popsci.com