Any of the flowering plants (angiosperms) and the conifers and related plants (gymnosperms). Seed plants share many features with ferns, including the presence of vascular tissue (seexylem and phloem), but unlike ferns, they have stems that branch sideways and vascular tissue that is arranged in strands (bundles) around the core. Seed plants have generally more complex plant bodies and reproduce via seeds. As the main dispersal unit of seed plants, the seed represents a significant improvement over the spore, with its limited capacity for survival. Seed plants also differ from ferns in having gametophytes that are reduced in size and are embedded in the sporophytes (and thus are less vulnerable to environmental stress). Another land-based adaptation of seed plants is pollen dispersed by wind or animals. The dispersal of pollen, in addition to dispersal of seeds, promotes genetic recombination and distribution of the species over a wide geographic area.