There are more than 250,000 species of plants on Earth.  Plants play a role in the survival of most organisms including humans.

Characteristics of Plants

Plants are eukaryotic multicellular organisms that have adapted succefully to life on land.  They are found in nearly every environment on Earth, including the most extreme conditions of the deserts of Africa and the frozen grounds of Antarctica.  While most plants live on land, some are also found in our near bodies of water.

Plants range in size from mosses and ferns that are barely seen by the naked eye to the giant Sequoia trees towering up to a hundred meters.

Most plants are autotrophic, that is, they produce their own food.  They contain chlorophylls a and b that enable them to capture sunlight and perform photosynthesis.  However, not all plants are green.  They may contain other pigments that mask the chlorophyll, thereby giving them a different color.

Some plants exhibit alternation of generations in their life cycle.  The alternating generations are called sporophyte generation and gametophyte generation.  The large plants that we see are the sporophytes.  The diploid sporophyte (spore plant) produces haploid spores that develop into haploid gametophytes.  The gametophyte is much reduced in size.  In flowering plants, the male gametophyte is the pollen grain (microgametophyte) and the female gametophyte is the embryo sac (megagametophyte) that is found inside the ovule.  The haploid gametophytes (gamete plants) produce gametes that fuse during fertilization and grow into new diploid sporophytes.

Classification of Plants

Plants are classified into two major groups: the nonvascular plants and the vascular plants.

1.      Nonvascular plants (Bryophytes) are plants that lack conducting tissues.

o       Bryophytes are small plants that thrive in damp places.  They may be found near water bodies, such as ponds, rivers, lakes, streams, and oceans.  Mosses, hornworts, and liverworts belong to this group.  Mosses also dominate te mossy forests.

o       Bryophytes do not have xylem and phloem for the transport of water and food through these plants.  Due to the absence of conducting tissues, they are only few cells thick and do not grow as tall as vascular plants.  They directly absorb water from their environment through their cell walls.  Bryophytes do not have true roots, stems, and leaves.  The rootlike structures that attach them to their substrate are called rhizoids which are thin filaments of elongated cells.

o       Bryophytes have also leaflike parts and stalks that look like stems.  They grow from spores instead of seeds.  The familiar leafy shoot of moss plant is the gametophyte generation.

o       Mosses, liverworts, and hornworts are very important for ecological succession.  They are called pioneer species, organisms that are the first to move into new areas, such as burned-out forests and lava fields.  As mosses die, decaying plant materials provide nutrients for other plants.  In effect, mosses change the condition of the environment so that larger plants can survive.

2.      Vascular Plants are plants that have conducting tissues, such as the xylem and the phloem.  More than 80% of all living plant species are vascular plants.  There are four major groups of vascular plants: seedless vascular plants, vascular plants with seed, vascular plants with naked seeds, and vascular plants with protected seeds.

o       Seedless Vascular Plants : Ferns and Fern Allies.  Seedless vascular plants are similar to mosses because they reproduce by means of spores.  But unlike mosses, they conduct fluids in their bodies by means of specialized tissues, such as the xylem and the phloem.  The presence of these vascular tissues enable them to grow bigger and thicker like the rest of the vascular plants.  Representatives of this group include the “true” mosses (club moss, spike moss), horsetails and ferns.  Ferns (pterophyta) make up the largest group of seedless vascular plants.  In tropical rainforests, tree ferns may grow up to five meters in height.  The green, leafy plants that we usually observe is the sporophyte generation of fern.  A fern plant consists of an underground stem or rhizome with small adventitious roots and clusters of several leaves or fronds and tightly coiled young fronds called fiddleheads.

o       Vascular Plants with seed.  Rice and corn are staple foods in the Philippines and in many parts of Asia.  Basically, foods that make up our daily meal come from seed plants.  There are 250,000 known species of seed plants in the world today.  Seed plants have true roots, stems, leaves, seeds and vascular tissues.  Most of the largest plants in the world belong to the seed plants.

o       Gymnosperms : Vascular Plants with Naked Seed.  Gymnosperm comes from a Greek term meaning “naked seed”.  The seeds of gymnosperms are not enclosed in a flower or a fruit.  Instead, they are found on the scales of female cones.  Conifers (pines, spruces, sequoias, and cedars) form the largest group of gymnosperms.  Some conifers produce both male and female cones on the same tree.  Other species produce male and female cones on separate trees.  Most gymnosperms have green, needlelike leaves that last for several years.  The oldest trees alive today belong to this group.

o       Angiosperms : Vascular Plants with Protected Seed.  Unlike gymnosperms, the seeds of angiosperms are enclosed in a fruit.  Since a fruit comes from an ovary of a flower, all angiosperms bear flowers.  Thus, they are also called the “flowering plants” (Division Anthophyta).  Most of the plants we are familiar with are angiosperms.  Angiosperms are divided into two classes: (1) monocots (Monocotyledonae) with one seed-leaf and the dicots (Dicotyledonae) with two seed leaves.

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2. Taxonomy: Kingdom Protista
3. Taxonomy: Kingdom Mycetae (Fungi)
4. Taxonomy: Kingdom Animalia
5. Taxonomy: Brief History of Taxonomy