Silky oak, Grevillea robusta, is a medium to fairly large tree with light gray, rouge, bark with mainly closely spaced furrows The trunk tends to be straight and tall Flowers form on the plant in season (in Hawaii, April and May) and extend through the summer Flowers are striking, abundant, and yellow to orange Leaves are distinctive andSilky oak Silky oak, also called Silk Oak, ( Grevillea robusta ), large tree native to Australia and also grown as a street tree in warm areas and, in its juvenile stage, as an indoor pot plant It belongs to the family Proteaceae ( see Proteales ) Silky oak ( Grevillea robusta ) In Australia it is cut for timber, but elsewhere it is valuedFastgrowing and stately, Grevillea robusta (Silky Oak) is an evergreen tree of great beauty Pyramidal when young, it develops a few horizontal limbs when older, giving it a broader top Mature specimens produce a striking display of large, rich, bright golden orange flowers, up to 5 in long (12 cm), in dense, onesided s...