HARDHACK (Spiraea to mentosa), a North American shrub of the rose family (Rosa ceae), called also steeple-bush, native to open grounds from Nova Scotia to Manitoba and southward to Georgia and Kansas. It has an upright, woolly, red dish-brown stem, 2 to 4 ft. high, bearing ovate, pointed, sharply toothed leaves, which are greyish or yellowish woolly beneath, and a slender, steeple-like flower-spike crowded with tiny deep pink flowers, blooming in late summer. The hardback, which is some times planted for ornament, is especially abundant in eastern New York and New England, where in many localities it occurs in weedlike profusion, becoming pestiferous in meadows and pastures. (See SPIRAEA.)