Hemionitis arifolia

Native to humid tropical forests across South and Southeast Asia, this small fern is immediately recognisable by its perfectly heart-shaped sterile fronds perched on slender, near-black stems. It grows as a lithophyte or low epiphyte — clinging to mossy rocks and tree bases in the forest understorey — which explains why it thrives in the steady moisture of a closed terrarium. It does best at 18–28 °C with humidity above 60%; drop below that and the fronds curl within hours. Its compact size (rarely exceeding 20 cm) makes it one of the most useful foreground plants for detailed terrarium compositions.