Fronds are thick. Not delicate. But robust. The Poor Knights spleenwort grows on volcanic cliffs and in caves where humidity remains high year-round. Its fronds are narrow and leathery, coloured dark green, clinging to rock faces. This robust appearance helps it survive in exposed maritime environments. The species inhabits volcanic cliffs and caves on the Poor Knights Islands. It prefers humid sheltered sites with minimal light. Unlike mainland ferns that require soil, this species anchors itself in rock crevices. Spores are produced on the underside of fertile fronds in linear sori. These spores are released into still cave air or windy cliff faces, settling on nearby rock surfaces where moisture allows germination. Diet consists of nutrients obtained through photosynthesis and absorption from sea spray and rock weathering. The fern does not consume organic matter directly but rather extracts minerals from salt water and volcanic rock. This halophytic and lithophytic lifestyle allows it to thrive in nutrient-poor coastal environments where other plants cannot establish. Classified as Nationally Critical, the Poor Knights spleenwort faces an extremely uncertain future. Its distribution is extremely limited, confined to the Poor Knights Islands. Climate change may alter humidity levels affecting survival. Invasive species such as rats threaten seedlings. Habitat modification from historical activity has reduced suitable cave habitat. Each threat compounds the others. The Poor Knights spleenwort has nowhere else to go. It is endemic to these islands. If it disappears here, it disappears everywhere. Conservation efforts focus on protecting remaining cave and cliff habitat from disturbance.