Which is NOT a nonvascular seedless plant? moss grass liverworts hornworts

You just answered your own question. Nonvascular seedless plants are devided into three groups, those three being mosses, liverworts, hornworts. These plants do not have vascular tissue (or if present, it is very reduced). As such plants they lack substantial vasculatur, are generally small in size. They lack structural support and mostly grow close to the ground in moist areas, and lack significant water-conducting cells.

Plants without vascular system are non-vascular plants. Non-vascular plants have no xylem and no phloem. Non-vascular plants include algae, bryophytes, moss grass, liverworts and hornworts. The answer to this item is moss. Moss is a non-vascular plant which has no seeds and no flowers. It uses spores in reproduction.