For the question of how angiosperms are well adapted to land, a basic
botany text usually discusses how plants are well adapted to land. Do
you want adaptations specific to angiosperms or reasons why terrestrial
angiosperms are better adapted to land than gymnosperms or seedless
vascular plants? Try a google.com search for angiosperm adaptations or
angiosperm success.

Here's one of several articles you will find,

Crepet, William L. 2000. Progress in understanding angiosperm history,
success, and relationships: Darwin's abominably "perplexing
phenomenon." Proceedings of the National Academy of Sciences 97:
12939-12941.
http://www.pnas.org/cgi/content/full/97/24/12939
http://www.pnas.org/cgi/reprint/97/24/12939.pdf

On the question, What role do plants have in maintaining biodiversity
and in the survival of humans(ecological and economical)?, try a
google.com search for plant importance, "importance of plants" or
economic botany.

David R. Hershey

wrote:
Hi,
I have a question

Angiosperms are considered to be the most highly evolved plants. How
are they well adapted to land?

answer how plant structures are adapted to their fuction,

and one more question

What role do plants have in maintaining biodiversity and in the
survival of humans(ecological and economical)?

thanks