Most premitive vascular plants are pteridophytes. Cycas belongs to gymnosperms. Gymnosperms have a well-differentiated plant body with vascular tissues. They produce naked seeds. Hence, option A is incorrect. Moss belongs to bryophytes. Bryophytes have a well-differentiated plant body with stem and leaf-like structures. But there is no specialized vascular or mechanical tissue. Therefore, option C is incorrect. Brown algae belong to thallophytes. Thallophytes do not have well-differentiated plant body and vascular tissues. Therefore, option D is incorrect. Ferns belong to pteridophytes. Pteridophytes have a well-differentiated plant body with vascular tissues. Therefore, option B is correct.