Asplenium antiquum
Asplenium antiquum is a fern of the group known as bird's-nest ferns. In Japanese it is known by "ō-tani-watari " and "tani-watari". Description. "Asplenium antiquum" is an evergreen fern, 2–3 ft. (60–90 cm). It has bright green, arching blades with a pointed end and a strong midrib. "Asplenium antiquum" can readily be distinguished from the closely related "Asplenium nidus" by its fronds of uniform width. Chemical composition. Mearnsetin 3,7-dirhamnoside, a glycoside of the flavonol mearnsetin, can be found in "A. antiquum". Taxonomy. A global phylogeny of "Asplenium" published in 2020 divided the genus into  eleven clades, which were given informal names pending further taxonomic study. "A. antiquum" belongs to the ""Neottopteris" clade", members of which generally have somewhat leathery leaf tissue. While the subclades of this group are poorly resolved, several of them share a characteristic "bird's-nest fern" morphology with entire leaves and fused veins near the margin. "A. antiquum" belongs to one of these subclades, together with "A. antrophyoides", "A. cymbifolium", "A. humbertii", and "A. phyllitidis". Other bird's-nest ferns, such as "A. nidus" "sensu lato" and "A. australasicum", form a separate subclade which is not particularly closely related. Distribution. The fern  is native to temperate East Asia, in China, Japan, Korea, and Taiwan on cliffs, dark forests, and tree trunks. It is an IUCN endangered species in its native habitats. Cultivation. The fern is commonly available in the plant nursery trade as an ornamental plant in subtropical climates, and a house plant in the United States and Europe in zones 9 and 10. It requires high humidity and bright indirect light, so does best in a greenhouse or terrarium if grown indoors. It needs regular watering and can do with minimal soil (similar to an orchid). The soil should always be  humid but not soaking wet.