Definition of Ulotrichales
: an order of green algae that includes the family Ulotrichaceae and in some classifications also Ulvaceae and that comprises freshwater or marine forms having a multicellular thallus with usually simple or branched filaments sometimes aggregated to form pseudoparenchymatous masses or sheets, asexual reproduction effected by zoospores, and sexual reproduction by fusion of isogametes or of differentiated egg and sperm cells
