Athyrium filix-femina is now commonly split into three species, typical A. filix-femina, A. angustum (narrow lady fern) and A. asplenioides (southern lady fern). Athyrium filix-femina is cespitose (the fronds arising from a central point as a clump rather than along a rhizome). The deciduous fronds are light yellow-green, 20–90 centimetres (7.9–35.4 in) long and 5–25 cm (2.0–9.8 in) broad. Sori appear as dots on the underside of the frond, 1–6 per pinnule. They are covered by a prominently whitish to brown reniform (kidney-shaped) indusium. Fronds are very dissected, being 3-pinnate. The stipe may bear long, pale brown, papery scales at the base. The spores are yellow on A. angustum and dark brown on A. asplenioides. A. filix-femina is very hardy, tolerating temperatures as low as −20 °C (−4 °F) throughout its range