The stamens in Lilium (true lily) have anthers that often form a "T" shape, and a "knob" (stigma) at the end of the style.

Daylily (Hemerocallis) stamens tend to all curve in the same direction, the anthers are never right-angled and the stigma is less obvious.

True lilies have small leaves spaced along the length of the flowering stem.

Daylilies have long leaves emerging together from the ground instead of small leaves along the stem, which is almost bare and often branched.

True lilies grow from a  scaly bulb.

Daylilies have roots, many thickened, which are attached to a crown, or rhizome.  There is no bulb.