這兩個島嶼之上僅被草原覆蓋，而這植被於香港的離島中擁有相當高的代表性。
因應這兩個島嶼上的環境，能推繼出新界的草原非因氣候所形成，而是由經常性的山火所引致。
這兩個島上的植物品種都會因以下兩個特殊情況而有所限制。分別是因受到風吹所帶來的鹽份所影響及因陡峭的岩石坡上土壤極少，降雨因快速流走和日照而變得相當干旱。
從兩個島嶼的地貌都可見海蝕作用的巨大影響力，而島嶼的東部比在西部受到更強的海蝕。 而火石洲東岸的玄武岩特別壯觀，具有相當高的地理價值。

The vegetation on these two islands is representative of many of the off-shore islands of Hong Kong which are covered exclusively by grassland.
A consideration of the environmental conditions existing on these islands suggests that the grassland in the New Territories is not a climax but is maintained by frequent hillfires.
The grassland community on these two islands is a vegetation type which is limited by extreme exposureto wind, often salt-laden; by the rocky, steep slopes carrying only shallow soils and by being subject to extremes of dyness due to the quick runoff of rainfall and the exposure to direct insolation.
The landform of both the island shows clearly that the influence of sea waves on the islands is much stronger on the eastern side than on the western. The basalt on the eastern coast of the Basalt Island is especially spectacular and is of geographical interest.