Marattia purpurascens is a large fern belonging to Class Marattiaceae. It has a globular rhizome with stipule-like fleshy outgrowths. The leaves are dark green, twice pinnate and up to 1 metre long. Every pinnule has up to six pairs of leaflets. The petioles are dark-purplish, hence the name 'purpurascens' meaning 'becoming purple'. The sporangia are fused in all Marattia into a bivalvate synangium.
Conservation plans have been proposed for Marattia purpurascens, an endemic of the distant Ascension Island in the South Atlantic, where a single population remains on Green Mountain. This population is now believed to be more stable than previously feared, but long-term threats to its survival do exist, in the form of competition with alien invasive species like introduced plants such as Lantana camara L. and grazing by sheep.