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All members of the Plant Kingdom (Green, Brown and Red Algae, and terrestrial plants) have their life cycle divided into two interchangeable phases: the gametophytic generation (responsible for the sexual reproduction through gamets) and sporophytic generation (responsible for the assexual propagation through spores).
The sporophytes are diploid plants responsible for the production of spores, and thus the generation of new gametophytes. The spores are originated from the reduction of diploid cells, and so are haploid cells that will most likely be carried away by wind, water or animals.
The morphology of sporophytes vary a lot from group to group, and the evolution of all major groups of plants can be illustrated by the evolution of the sporophyte.
In some Algae, gametophytes and sporophytes are quite similar and independant, although in Brown and a few Green algae they may have differences.
Bryophytes have very reduced sporophytes, with only a stalk and a capsular sporangium, no leaves or roots, often even without chlorophyl. They have limited growth (except in Anthoceros), and are completely dependant on the gametophyte to get nutrients and water.
Pteridophytes shows a total turnover from the bryophyte stage, with big and complex sporophytes. They are only dependant on the gametophyte in very early stages, and the adult sporophyte have roots, stem, leaves, a vascular system, and several kinds of sporangia. We all cultivate ferns for their sporophytes.
Gymnosperms and Angiosperms have sporophytes that are completely independent from the gametophytes. In fact, the gametophyte is now completely dependent on the sporophytes, reduced to a few cells that form the pollen grains and ovules. The spores of these plants are very short lived, and are kept to germinate on special leaves (the scales of a pine cone, or carpels in a fruit). All pines, flowering plants, herbs, shrubs, climbers, trees, etc. are the sporophytic generation of those species.
For more information, see "spores", "diploid", "gametophyte", and check out the deffinition of all the major groups of plants.
