ersity of form within the angiosperms has contributed to their successful colonization of more habitats than any other group of land PLANTS. Gymnosperms (the nonflowering seed plants) are only woody plants with a few woody twining vines. There are few herbaceous or aquatic gymnosperms; most gymnosperms do not occur as swampy vegetation or in marine habitats. With the exception of cycads, gymnosperms have simple leaves, and none are modified as spines, tendrils, or storage organs.The absence of substantial diversity in the vegetative features of gymnosperms appears to have limited their ability to adapt to diverse or extreme habitats. The absence of xylem vessels in most gymnosperms, and hence the less EFFICIENT water transport system than that FOUND in the angiosperms, is one EXAMPLE. In fact, the only gymnosperms with vessels, the Gnetales, is the only group that contains vines and the only group that deviates from the usually woody trunk growth form. The absence of vessels in angiosperms, however, is rare; the few groups without vessels are small trees or shrubs with limited distribution, as in the Winteraceae. Another FACTOR contributing to the limited distribution of gymnosperms is that they do not produce reproductive structures until several years after the seed germinates; therefore, a woody habit is required to achieve sexual maturity. Finally, the gymnosperms also require a relatively stable environment for growth. Thus, restraints imposed by anatomy and life cycle have probably limited morphological diversity among the gymnosperms.Ϧ០ᖰ៩ ɨƬ'ន Ϧ៩ɭᖰ ⩏ Ϧ♬⩔៩ ♬ Ɯ០⩎ᖱ៩Ʀ⨏⩏ɭ ᖱ♬ƴ