What did forests look like millions of years ago?
The trees you see today did not exist. Nonvascular plants and vascular seedless plants first dominated the forest. The remains of these forests formed the coal that we depend on today.
Nonvascular Seedless Plants
Nonvascular seedless plants, as their name implies, lack vascular tissue. Vascular tissue is specialized tissue that transports water, nutrients, and food in plants. As they lack vascular tissue, they also do not have true roots, stems, or leaves. Nonvascular plants do often have a “leafy” appearance, though, and they can have stem-like and root-like structures. These plants are very short because they cannot move nutrients and water up a stem.
Nonvascular seedless plants, also known as bryophytes, are classified into three phyla:
Mosses are most often recognized as the green “fuzz” on damp rocks and trees in a forest. If you look closely, you will see that most mosses have tiny stem-like and leaf-like structures. This is the gametophyte stage. Remember that a gametophyte is haploid, having only one set of chromosomes. The gametophyte produces the gametes that, after fertilization, develop into the diploid sporophyte with two sets of chromosomes. The sporophyte forms a capsule, called the sporangium, which releases spores (Figure below).
Sporophytes sprout up on stalks from this bed of moss gametophytes. Notice that both the sporophytes and gametophytes exist at the same time.
Hornworts are named for their appearance. The "horn" part of the name comes from their hornlike sporophytes, and “wort” comes from the Anglo-Saxon word for herb. The hornlike sporophytes grow from a base of flattened lobes, which are the gametophytes (Figure below). They usually grow in moist and humid areas.
In hornworts, the “horns” are the sporophytes that rise up from the leaflike gametophyte.
Liverworts have two distinct appearances: they can either be leafy like mosses or flattened and ribbon-like. Liverworts get their name from the type with the flattened bodies, which can resemble a liver (Figure below). Liverworts can often be found along stream beds.
Liverworts with a flattened, ribbon-like body are called thallose liverworts.
bryophyte: Type of plant that lacks vascular tissues, such as a liverwort, hornwort, or moss.
gametophyte: Haploid (having one set of chromosomes) generation in the life cycle of a plant.
hornwort: Nonvascular plant with long and pointed sporophytes, like tiny horns.
liverwort: Nonvascular plant that has leaf-like or ribbon-like bodies.
moss: Tiny nonvascular plant that grows like carpets and has leaf-like structures.
nonvascular seedless plant: Plant without vascular tissue or seeds.
sporangium: Capsule that releases spores in mosses.
sporophyte: Diploid (having two sets of chromosomes) generation in the life cycle of a plant.
vascular tissue: Specialized tissue that transports water, nutrients, and food in plants.
- Nonvascular plants lack seeds and vascular tissue.
- Nonvascular plants include the mosses, the hornworts, and the liverworts.
Use the resource below to answer the questions that follow.
- How do bryophytes keep their eggs from drying out?
- How does bryophyte sperm locate the bryophyte egg?
- What happens in the archegonia?
- What happens in the antheridium?
- Where does fertilization of the bryophyte egg occur?
- What are examples of nonvascular plants?
- Why do nonvascular plants tend to be very short?