Asexual reproduction is not an advantage seeds provide over spores. Spores provide a means of asexually producing and dispersing offspring. Production of a seed requires sexual reproduction.
a) Spores are usually single-celled, whereas seeds are multicellular.
b) The multicellular seed consists of an embryo protected by a layer of integument, the seed coat.
c) A seed can remain dormant for days, months, or even years after being released from the parent plant, whereas most spores have shorter lifetimes.
d) Also, unlike spores, seeds have a supply of stored food. If conditions are favorable where it lands, the seed can emerge from dormancy and germinate, with its stored food providing critical support for growth as the sporophyte embryo emerges as a seedling."