Flowers are "conscious" in the sense that they respond to their environment, and more often than not in a way that helps promote their survival.

Even a single lone electron has a limited sense of consciouness, in the sense that it has two possible energy states, a positive and negative spin, and absorbing or emitting energy can alter that state.

More complex systems have more sophisticated responses. Even insects are studded with sensors, many of them totally alien to us, they are constantly gathering and evaluating data from their environment, and have a sophisticated palate of responses they have evolved to select from when responding to it.

The point Russell makes is that this ability to respond appropriately to the environment seems to be a property of all matter to a certain extent, from sentient beings to fundamental particles. This seems to be the one property the entire universe shares.