Living species are mostly aquatic or semi-aquatic, and are found in clear ponds and slowly moving streams.

Each leaf is slender and broadens downward to a swollen base up to 5 mm wide where the leaves attach in clusters to a bulb-like, underground corm characteristic of most quillworts.

This swollen base also contains male and female sporangia, protected by a thin, transparent covering (velum), which is used diagnostically to help identify quillwort species.

[1] Some authors include the tree-like "aboresecent lycophytes", which formed forests during the Carboniferous period, and often assigned to their own order, Lepidodendrales, within Isoetales.

[5] The oldest fossil closely resembling modern quillworts is Isoetites rolandii from the Late Jurassic of North America.