<正>Notothylas Sull.is a phyletically isolated yet interesting genus of hornworts belonging to the family Notothyladaceae.It is the smallest of all the hornworts,with a pale to dark green gametophytic thallus that is seldom more than 2-3 centimeter in diameter,usually much smaller. Hence it is usually overlooked in the field.It is also unusual among hornworts in that the sporophyte is fusiform or slenderically elliptical,usually just 2-4(- 5.5) mm long,but could be as small as 1.5 mm(N.himalayensis Udar & D.K.Singh) and may,or may not,have a columella. The sporophytes grow outwards rather than upwards,and there are no stomata on the surface of the sporophytes.The elaters are irregularly subglobose,more or less similar in appearance and size to the spores.