My text book claims all land plants undergo alternation of generation. However, I don't see how it could be with dandelion. The flower head gets pollinated and then turn back on itself. After a while it opens back as a seed head ready to blow seed in the wind. What would be the spores then? And the gametophyte organism? All seeds are a result of sperm and ovula so it would mean the dandelion flower is a sporophyte?
Dandelions are sporothytes. In Wikipedia you can read (Alternation of generations):
"In the spermatophytes, the seed plants, the sporophyte is the dominant multicellular phase; the gametophytes are strongly reduced in size and very different in morphology. The entire gametophyte generation, with the sole exception of pollen grains (microgametophytes), is contained within the sporophyte. The life cycle of a dioecious flowering plant (angiosperm), the willow, has been outlined in some detail in an earlier section (A complex life cycle). The life cycle of a gymnosperm is similar. However, flowering plants have in addition a phenomenon called 'double fertilization'. Two sperm nuclei from a pollen grain (the microgametophyte), rather than a single sperm, enter the archegonium of the megagametophyte; one fuses with the egg nucleus to form the zygote, the other fuses with two other nuclei of the gametophyte to form 'endosperm', which nourishes the developing embryo. For further information, see Double fertilization"