Broad fungal compatibility and seed size may facilitate invasiveness in two Asian terrestrial orchids Spathoglottis plicata and Arundina graminifolia

Two Asian orchids, the bamboo orchid ( Arundina graminifolia ) and the Philippine ground orchid ( Spathoglottis plicata ), are expanding into South and Central America, the Pacific, and Africa. Here, we tested whether seed traits and low in vitro selectivity toward mycorrhizal fungi may contribute to their successful spread outside the native range. We examined seed size and reserves, asymbiotic and symbiotic germination with orchid mycorrhizal fungi from different geographic regions. Both species have relatively large seeds, with A. graminifolia having some of the largest among orchids. Seeds contain lipids, proteins, and low amounts of soluble saccharides and starch. Despite these reserves, both orchids are initially mycoheterotrophic and require an external carbon source for early development. In asymbiotic culture, both species showed high germination on sucrose‐containing media, with maximum germination exceeding 95%. In symbiotic culture, both species formed protocorms with Tulasnellaceae isolates from different continents, including isolates obtained from locations separated by more than 9000 km. This capacity was broader in S. plicata . Our results suggest that the success of S. plicata outside its native range may be facilitated by broad compatibility with Tulasnellaceae, some of which have a global distribution, and partly by self‐pollination. In A. graminifolia , relatively large seeds may provide greater internal reserves for early development, but this species appears more specific toward certain Tulasnellaceae lineages and remains pollinator‐dependent. Together with the ability to colonize disturbed habitats, these traits may help explain the successful spread of both orchids outside their native range.