Non-vascular plants are true plants; they have cell walls, undergo photosynthesis and reproduce.
The characteristic defining a non-vascular plant is the lack of vascular tissues such as roots or a stem, this causes them to be much smaller than vascular plants and includes hornworts, liverworts and the mosses. They take in water through cell walls and transfer it between cells using osmosis. The movement of gases and minerals is powered by diffusion.
Non-vascular plants inherited their reproductive cycle from algae and it is called the alternation of generations. Through a non-vascular plants life, it will take on two forms; the first is the gametophyte, which sexually reproduces to produce the sporophyte which then asexually reproduces to create the new plant.
While they can’t grow as tall as trees, they have lived on earth for 475 million years making non-vascular plants a truly successful organisms.
From Crash Course: Biology on YouTube presented by Hank Green.