Byblis filifolia is a carnivorous plant endemic to Northern Australia. The species is named for its threadlike leaves.

Byblis filifolia is a large plant, with stems that reach 30-60cm in height. In nature, the plants are typically single-stemmed, although old plants in cultivation are known to branch. The leaves are long and slender, with reasonably well-spaced internodes between leaves. The flowers are around 2-3cm in diameter and lilac in colour. The anthers are longer than their supporting filaments. Some forms have yellow-striped backs of the petals. The glands on mature leaves and pedicels are typically on short to medium-length tentacles. The species is very variable in morphology, with many location-specific forms.

The species is endemic to Northern Australia. It is most common in the Kimberley Region of Western Australia, extending into the Northern Territory. It grows in seasonally moist niches such as herbfields in seepage areas, sand plains and soaks around rocky outcrops.

Byblis filifolia is similar to other annual Byblis species in Australia’s tropical north. In the first instance, it is distinguished from B. liniflora and B. aquatica by its larger size and filaments that are shorter than the anthers (B. aquatica and B. liniflora are small, with filaments that are longer than the anthers). It is distinguished from B. rorida by its well-spaced foliage and sepals lacking very long tentacles (B. rorida is compact with very long tentacles on the sepals). It is distinguished from B. pilbarana by its larger seeds (Those of B. pilbarana are small for the genus). It is distinguished from B. guehoi by its non-branching to sparsely branching erect stems (B. guehoi is highly branching and spreads along the ground).