Nonvascular plants are the simplest land plants that lack internal water transport systems. They first evolved around 460 million years ago from green algae. They reproduce both sexually, with gametes developing in protective structures, and asexually through regeneration. Nonvascular plants are typically found in damp, shady areas as they cannot survive drying out and lack means to transport water over long distances. There are three divisions of nonvascular plants that share some characteristics but are distinct in other ways.
2. • Nonvascular plants are the simplest of all land dwelling plants. Like their closest
ancestors, the green algae, they lack an internal means for water transportation. They
also do not produce seeds or flowers. They generally only reach a height of one to two
centimeters, because they lack the woody tissue necessary for support on land.
3. EVOLUTIONARY HISTORY
• Scientists possess fossil records that lead them to believe that plants evolved during four
distinct periods. Nonvascular plants arose first, during the late Ordovician period of the
Paleozoic Era, approximately 460 million years ago. Their closest non plant ancestor is a
type of green algae called charophytes.
• Scientists also believe that living in shallow water was a preadaptation to living on
land. Natural selection probably favored algae (living on the fringes of bodies of water)
that could survive through periods when they were not submerged. Waxy cuticles and
jacketed organs, both characteristics of nonvascular plants, are possible adaptations that
the algae developed to survive in these conditions.
4. REPRODUCTION
• Nonvascular plants can reproduce both sexually and asexually. Asexual reproduction is
the less common method. It basically consists of the regeneration of plant material,
leaves or other parts, that fall to the ground and generate secondary plants which bear
new buds.
• Most nonvascular plants, though, reproduce sexually. Their gametes develop within
structures called gametangia, which are organs that have protective jackets of sterile cells
that prevent the gametes from drying out during development.
5. HABITATS
• Nonvascular plants are almost always found in damp, shady places. They have little or
no resistance to drying, and because they lack vascular tissue they cannot carry water
from the ground to the aerial parts of the plant. Like sponges, they must imbibe the water
lying on their surfaces and distribute it by the relatively slow means of diffusion, capillary
action, and cytoplasmic streaming. Therefore, they cannot survive for very long in areas
that are not constantly moist. Some can survive in alternative habitats such as sand
dunes, but the majority thrive in dark, dank places. Because of their limited range of
terrestrial habitats, nonvascular plants have never dominated much of the earth's
landscape.
6. ENERGY ACQUISITION
• Like most plants, nonvascular plants acquire energy through photosynthesis. During this
process, the plant converts light energy into chemical energy, then proceeds to store it in
the form of glucose or other organic compounds.
7. DIVISIONS
• There are three divisions of nonvascular plants: Bryophyta, Hepatophyta, and
Anthocerophyta. Until recently, scientists grouped all three together as one division,
Bryophyta, but the current view is that they are probably not related. They do share some
key characteristics, such as the presence of a waxy cuticle and gametangia, but they all
have distinct characteristics that warrant separate divisions.
