Gymnosperms: General characters, Origin, habit, reproduction, smallest & tallest скачать в хорошем качестве

Gymnosperms: General characters, Origin, habit, reproduction, smallest & tallest

Gymnosperms are plants with naked seeds (Gymno = naked, sperma = seed). In evolutionary hierarchy, they are placed in between pteridophytes and Angiosperms. Phanerogams without ovary Origin: Devonian Period of Paleozoic era (Geological Time Scale) Distribution: Temperate and tropical regions of the world Diversity: 70 Genus and 725 species (living) Habit: All are woody, perennial forms Habitat: High altitude and desserts or Xeromorphic/ xerophytic Forms: Shrub, trees, climbers (Lina) Root: Tap Root System (with or without coralloid roots) Stem: Unbranched (Cycas) or Branched (Pinus) Branches: Dimorphic, branches of Limited growth and of Unlimited growth Leaves: Compound (Cycas), Needle like (Pines), Simple (Gnetum) Dimorphic (Scaly and photosynthetic) Stele: Siphonostele Wood: Pycnoxylic in Coniferales (dense) Manoxylic in Cycadales (less developed) Xylem: Tracheid only (vessels in Gnetales) Phloem: Sieve tube and Phloem parenchyma (Companion cells absent) Reproductive organs: In compact, non-attractive cones. Plants usually dioecious (Unisexual), Heterosporous Male cone: Small, herbaceous, with microsporophyll Female cone: Large, woody, perennial Ovule: Naked, orthotropous, Unitegmic Pollination: Anemophilous (Wind) Seeds: Naked Tallest: Sequoia sempervirens Smallest: Zamia pygmaea