Silicon nanowires (SiNWs) grown from 'sunflower-seed'- and 'mushroom'-shaped particles have been observed by electron microscopies. The SiNWs were synthesized by thermal evaporation of SiO powders without any metal catalysts. The SiNWs grown on the sunflower-seed-shaped particles had sub-branches of SiNWs terminated by Si bulbs. The SiNWs on the mushroom-shaped particles were densely and uniformly distributed on the surface of the mushroom cone. The growth history suggests that these SiNWs were formed by nucleation which originated from the surface of amorphous SiO particle matrixes via phase separation and precipitation followed by growth through oxide-assisted vapor-soild reaction.