A colonial epiphyte with a twist: morphological differentiation and potential division of labour in the fern Platycerium bifurcatum

Division of labour, a hallmark of complex animal societies, remains poorly understood in plants. The staghorn fern (Platycerium bifurcatum, Polypodiaceae), a colonial epiphyte, offers a unique model to explore this phenomenon in plants inhabiting the challenging tree canopy. This study investigates how ramet position and colony size influence morphological differentiation and functional roles of strap fronds. By analysing 87 strap fronds across 29 colonies on Lord Howe Island (NSW, Australia), we found significant morphological differentiation along the vertical profile of the colony. Top-positioned ramets produce stiff, curved, erect strap fronds optimized for water capture, while lower-positioned ramets produce pendulous, flexible, flattened strap fronds better adapted to enhance photosynthesis in shaded conditions. Furthermore, reproductive allocation was highest in upper ramets, reinforcing a potential functional distinction across colony levels. Larger colonies exhibited greater morphological specialization, consistent with the size-complexity hypothesis, which predicts increased task specialization with colony size. Our findings provide new insights into the complex life history of the staghorn fern, offering a fresh perspective into how morphological differentiation contributes to emergent collective strategies in plants.