Algae is the categorizing name for millions of different algae species, including the largest and most diverse group known as green algae. Scientists believe that within the green algae group is a type of alga that is the ancestor of land plants. The evidence for this link can be seen in the similarities between green algae and bryophytes (liverworts, hornworts and mosses), which are the oldest land plants on Earth.
Dependence on Water
Plants have evolved ways to live on land, including developing a waxy cuticle that allows them to retain water. This waxy cuticle is absent in algae and bryophytes. As a result, these organisms tend to be extremely water-dependent. Algae usually live in water, but some types are able to live on land in very moist environments. Green algae, for example, live mostly in freshwater or on trees, rocks and soil. Likewise, bryophytes usually require an aquatic habitat or one rich in moisture, although there are some types of bryophytes that require very little water to survive.
Like algae, bryophytes are nonvascular. Vascular tissue is the conducting tissue (called xylem and phloem) that transports nutrients from the roots and leaves through the stem in most land plants. In nonvascular plants, like algae and bryophytes, this tissue is missing, as are true roots, leaves and stems. This similarity has caused scientists to regard the bryophyte as an intermediary in the evolution from algae to land plants. Another structural consideration is the cellular wall. Bryophytes, like other land plants, feature rigid cellular walls containing carbohydrate cellulose. This type of cell wall is also present in certain types of green algae.
Bryophytes, like most algae (including green algae), have photosynthetic pigments, such as chlorophyll a and b, which absorb and trap light energy from the sun and allow for the process of photosynthesis (the process by which a plant is able to synthesize sunlight, carbon dioxide, water and inorganic salts into the nourishment it requires to live).
Life Cycle and Reproduction
Like most algae, bryophytes have reproductive life cycles characterized by an "alternation of generations." Each generation or phase is the result of a shift between sexual and asexual modes of reproduction. In fact, this type of life cycle is common to all plants, though often a single generation lasts most of a plant's life. In sexual reproduction, bryophytes and algae, like animals and other plants, feature free-swimming (motile) sperm with whiplike flagella (the type of sperm "tail") that depend on water to be transported to a nonmotile egg.
- Royal Botanic Garden Edinburgh: Bryology (Mosses, Liverworts and Hornworts)
- Michigan Technological University; Bryophyte Ecology; Janice M. Glime; 2007
- The New York Botanical Garden; What Is a Bryophyte Anyway?; Shawn Krosnick and Kevin E. Indoe
- Tulane University; Lab 8: Primitive Plants-Bryophytes, Ferns and Fern Allies; Dr. Bruce E. Fleury
- Photo Credit Hemera Technologies/Photos.com/Getty Images