Small forget-me-not is an emergent aquatic forb, 10-40cm tall, with a terminal inflorescence that becomes open. Mature pedicels are spreading, equaling or mostly longer than the 3-5mm calyx. Flowers are pale blue with a yellow center, each limb (free part of petal) is 2-5mm wide. The calyx is closely covered with short, stiff, sharp hairs, and the lobes (teeth) are about the same length as the tube, styles are distinctly surpassed by the nutlets. Lower leaves are mostly oblanceolate, the others are more oblong or elliptic to lance-elliptic. Its stem is slender, often reclining, but not creeping, along the ground at the base. It is inconspicuously covered with short, stiff, sharp hairs.
It can be distinguished from the non-native M scorpoides by its corolla limbs, which are 2-5mm wide in M laxa and 5-10mm wide in M scorpoides. These species can also be distinguished by their calyx lobes, which are about as long as the rest of the floral tube in M laxa and much shorter than the rest of floral tube in M scorpoides.
