BISC 337 Lecture Notes - Lecture 13: Cycad, Ginkgoales, Gnetophyta

• School: Simon Fraser University
• Department: Department of Humanities Biological Sciences
• Course: BISC 337
• Professor: Aubrey Pearson

Document Summary

Four phyla of gymnosperms: cycadophyta, ginkgophyta, coniferophyta, gnetophyta. Date back to the permian (290 myo) Cycads are the last survivors of a previously more widespread and diverse group of. Distribution today restricted to tropical/sub-tropical regions: believed to have evolved from seed ferns. Leaves in a tight cluster at the terminal parts of the stem (rosette) Usually short plants with squat stem covered in leaf bases from shed leaves. Important for mechanical support: stem has a wide cortex and large pith, secondary growth is atypical, produces small amounts of vascular tissue, vascular tissue is dominated by parenchymal cells. Stem is not characteristic of the other gymnosperms. Present as crown at apex of plant. Pinnate with single series of leaflets: only gymnosperm to possess pinnate, fern-like leaves. Produce a root system derived from the embryonic root (not adventitious roots) Cycads also produce negatively geotropic (grow opposite to direction of gravity) roots.