Asplenium viride

Green spleenwort is a small, tufted fern of damp limestone and other lime-rich rock in the mountains of Europe, northern Asia and northern and western North America. It looks like maidenhair spleenwort, but its leaf stalks and midribs are green rather than dark brown. It is a fully hardy alpine that needs a cold winter, so it belongs in a shaded rock garden, an alpine trough or a crevice, not a warm room.