Correct option is C
Ans. (c) Rhynia major
Rhynia major is no longer considered a true vascular plant due to the structure of its conducting elements. The key characteristic that differentiates Rhynia from true vascular plants is the lack of secondary thickening in its conducting tissue. Secondary thickening, which is essential for the development of true vascular plants, is absent in Rhynia. It was initially classified as a vascular plant, but further examination revealed that its vascular tissue lacked the lignified secondary walls typical of true vascular plants, placing it outside the true vascular plant category.
Information Booster
Rhynia major: Rhynia was initially regarded as one of the earliest vascular plants. However, its conducting elements do not exhibit the secondary thickening that is characteristic of true vascular plants. This discovery led to a reclassification, and Rhynia is now considered a plant that lacks true vascular tissue.
Secondary thickening: Secondary thickening refers to the thickening of the cell walls of the vascular tissue that occurs after the plant has reached maturity. This thickening is essential for providing structural support and is a hallmark of true vascular plants. Rhynia's vascular tissue lacks this feature, which is why it does not meet the criteria for being classified as a true vascular plant.
Additional Information
Option (a): Asteroxylon mackiei is considered a true vascular plant. It exhibits secondary thickening, which is a key feature of vascular plants, supporting its classification as a true vascular plant.
Option (b): Lepidodendron licopodites is also a true vascular plant. It is a member of the extinct group of plants known as the lycophytes and exhibits secondary thickening in its vascular tissue.
Option (d): Sphenophyllum plurifoliatum is considered a vascular plant and demonstrates characteristics such as secondary thickening in its conducting elements, placing it within the group of true vascular plants.
