Angiosperm represent the highest point in plant evolution. Here is how/why

Plant evolution has tended toward specialization of the sporophyte. In angiosperms, the sporophyte achieved its highest degree of specialization; this is seen in the various structure that have been evolved.
The root has been highly developed with well organized vascular system made up of xylem and phloem tissues. Xylem has xylem vessels, with large lumen and pits. Phloem has sieve tubes and companion cells. All these extend into the stem and leaves and aid in efficient conduction of water and mineral element from soil to leaves. As well as translocation of food from leaves to other parts.
Stem is highly developed and undergoes secondary thickening to give adequate support to plant.
There is great diversification to suit all habitats; they have exploited the deserts (xerophytes), aquatic environment (hydrophytes), normal environment (mesophytes). In each case several modification have been made to suit the environment.
They have also evolved strategies to ensure reproduction outside water e.g various groups have specialised pollination agent; coloured and scented flowers (insect pollinator). They have specially shaped flower for a particular insect; some bear clusters of flowers for increased for increased efficiency of pollination at a time e.g heads and inflorescence in some group. Some have light powdery polles (wind polinated). Some flowers open only at specific time of the day which coincides with the activities of the adapted pollinator.
They have also evolved diverse mechanism to ensure fruit and seed dispersal which is done by various dispersal mechanism e.g by man, water explosive mechanism, etc. In each case special characteristic are developed.
Double fertilization occur only in this group of plants, this results in the formation if an eight nucleate embryo sac. Also forms endosperm which provides embryo with nourishment.

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