BSC 196 Lecture 15: BSC 196- Lecture 15
Document Summary
The origin of land plants starts with green algae in the group charophytes. Charophytes and plants share several morphological and molecular similarities: rings (not lines) of cellulose-synthesizing proteins, morphologically similar, flagellated sperm. Similarity of some genes, including chloroplast genes: note that land plants are not descended from modern charophytes, but share a common ancestor with modern charophytes. Charophytes were already located near edges of water and likely experienced periodic drying. In charophytes a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out. Sporopollenin is also found in plant spore walls. The movement onto land by charophyte ancestors provided unfiltered sun, more plentiful co2, and nutrient-rich soil. Land presented challenges: unpredictable water sources and lack of structural support. Five key traits appear in nearly all land plants but are absent in the charophytes: alternation of generations, multicellular, dependent embryos, walled spores produced in sporangia, multicellular gametangia, apical meristems.
