Nerine filamentosa has been considered a synonym of N. filifolia, but the two appear to be quite distinct. DNA studies should settle the question eventually.

Here are the two species, in profile, compared side by side:

Nerine filifolia	Nerine filamentosa

The filaments of N. filifolia extend beyond the face of the tepals for a distance less than the length of the flower from ovary to face of the tepals. For N. filamentosa, the filaments extend beyond the face of the flower by at least the length of the flower from ovary to face of the tepals.

Other Sources of Information

RHS Manual of Bulbs, John Bryan and Mark Griffiths, Eds., Timber Press (1995).
Bulbous Plants of Southern Africa, by Neil du Plessis and Graham Duncan, Tafelberg Pub. Ltd., Cape Town (1989).
"Nerines in Southern Africa", by Rachel Saunders, in HERBERTIA, vol. 52, p. 88 (1997).
Cape Bulbs, by Richard L. Doutt, Timber Press (1994).