Reduction in vascular tissue, mechanical tissue and cuticle is characteristic of

Hydrophytes live in water, which surrounds them and buoys them up.
They can absorb water over their whole surface, so there is little need for conduction; the vascular tissue, especially xylem, is poorly developed.
Water supports the plant body, so mechanical tissue (sclerenchyma) is reduced; instead there is abundant aerenchyma for buoyancy and gas storage.
There is no danger of losing water, so the cuticle is thin or absent.
Xerophytes show the opposite features: thick cuticle and well-developed vascular and mechanical tissues.
Hence these reductions are characteristic of hydrophytes.