Idaea straminata, the plain wave, is a moth of the family Geometridae.

The ground colour is pale greyish ochreous with scattered black speckles.

Both wings have a conspicuous though small black discal dot.

The postmedian line is often rather well-developed, marked with darker dots on the veins, on the hindwing it is not only sinuate inwards between the radials and again posteriorly, but is also more or less strongly angled on the first radial; the two lines or shades which edge the subterminal are usually (especially the distal) very ill developed or wanting.

On the under surface the forewing is a little darker, the hindwing a little whiter, the postmedian line and usually the median more strongly developed than above.