A step into the shadows: Evolutionary shifts in fruit structure and dispersal strategies in Asian mycoheterotrophic Ericaceae

Societal Impact Statement This study examines how the fruits of non‐photosynthetic forest plants in the Monotropoideae (Ericaceae) have evolved into the diversity observed today. By analyzing four Asian species, we identified a shift from dry, dehiscent fruits that release seeds into the air to fleshy, berry‐like fruits adapted for animal dispersal. This transition was likely driven by “a step into the shadows”: life in shaded, humid forest understories, where wind dispersal is less effective. The move toward animal‐mediated dispersal illustrates how even achlorophyllous plants can evolve new strategies, offering valuable insights into the links between plant form and ecology. Summary The fruit is a key evolutionary innovation in angiosperms, enabling diverse seed dispersal strategies. However, how fruit structure influences dispersal success remains poorly understood in rarely studied groups such as non‐photosynthetic mycoheterotrophic plants. Here, we examine fruit structure in the Monotropoideae (Ericaceae)—a lineage of mycoheterotrophic herbs with two fruit types: dehiscent capsules and indehiscent, berry‐like fruits. To decipher how fruit structure relates to dispersal strategy and evolution, we investigated fruit development and anatomy in four species that occur in Asia: Hypopitys monotropa , Monotropa uniflora , Monotropastrum humile , and Monotropastrum kirishimense . These species represent both capsule‐bearing and berry‐bearing lineages and together account for four of the seven monotropoid taxa recorded from Asia. Our results show that Monotropastrum shares key fruit traits with Monotropa , reflecting their close evolutionary relationship, whereas Hypopitys exhibits distinct features. We document an evolutionary shift from dehiscent capsules to indehiscent, berry‐like fruits, accompanied by a progressive loss of seed‐release mechanisms and reduction of hard tissue in the fruit wall. This shift was likely associated with adaptation to humid, shaded forest understories, where wind dispersal is less effective, as well as with intrinsic traits of these non‐photosynthetic plants, including their highly reduced vegetative and reproductive organs. The evolution of berries in Monotropoideae likely promoted endozoochory, a dispersal strategy that may be favored under these conditions.