Unlike the Sky Dragon whose elemental attributes seemed to be restricted to the 'weather' attributes, Lightning, Wind and Water, the Green Dragon seemed to be a bit more versatile.
Not only did it share a Wind attribute of the same strength, but it also had both Fire and Water attributes though somehow at a lower intensity, not to mention that it actually also had control over the 'Vegetation' attribute.
So far, the only reason I had heard of such an attribute was the legacy technique that I received after passing the 'Vegetation Trial', which was only supposed to be a hypothesized elemental technique to use both Water and Earth elements to synthesize Vegetation ones.