Plant Taxonomy

Taxonomy is a method used by scientists to classify all living things in order to better understand their evolutionary relationships. Taxonomy includes species descriptions and identification. Modern taxonomy originated in the mid-1700s, when Carl Linnaeus established a system to classify all living organisms. He did this by giving every species a two-part Latin-based name, also known as a scientific name. Linnaeus categorized plants based on their reproductive structures, in an attempt to better understand the evolutionary relationship between different plants.

All living things are grouped into broad categories called kingdoms. Plants are in the kingdom Plantae. Within a kingdom are many categories called phyla (singular is phylum). The Kingdom Plantae includes the phyla Chlorophyta (green algae), Bryophyta (mosses), Pteridophyta (ferns), Coniferophyta (conifers) and Magnoliophyta (flowering plants).

Chlorophyta – Green Algae

Although not technically plants, green algae are the organisms from which land plants evolved. Green algae include unicellular flagellates (single-celled organisms with tail-like structures), multicellular forms and macroscopic seaweeds – all of which can photosynthesize. Green algae are primarily aquatic; most commonly found in freshwater and marine habitats, but can also be found on trees and rocks. Some are also symbiotic (living in relationship) with fungi, forming what are known as lichens. The group of green algae most closely related to land plants is the Charophytes.

Bryophyta – Mosses

These are the most primitive true plants. Mosses lack a vascular system, meaning they do not have tissue (group of cells that work together to perform a specific function/role) to transport water throughout the plant. Instead, mosses acquire their water, nutrients and minerals by a process called osmosis, where water moves from areas with a lot of water to areas with less water. Since Bryophyta cannot easily carry water and nutrients throughout a large plant, mosses grow low to the ground (usually only a few centimeters high). Mosses also lack roots. Instead, mosses have rhizoids, which are root-like threads that help anchor the plant to the ground without absorbing nutrients and water.

Mosses usually live in damp and shady areas, and grow in clumps to form dense, soft masses of vegetation. Mosses are one of the first types of plants to become established on rocky ground. Like lichens, they are able to break down the rock, allowing the early stages of soil formation, which is essential for larger plants to grow. Mosses are able to absorb many times their weight in water, and help to prevent soil erosion by capturing rainfall.

Pteridophyta – Ferns

Still primitive, but more advanced than mosses, ferns do have a vascular system to transport water and nutrients throughout the plant. The vascular system includes tissues such as xylem (a transport tissue which moves water around the plant) and phloem (a transport tissue which moves nutrients – particularly sugar – around the plant). Ferns have roots that absorb water and nutrients from the soil, which then get transported to the stems and leaves via the xylem and phloem. Ferns are also known for their fiddleheads – the curled-up leaves of young ferns. Ferns grow in a variety of habitats, including on mountains, in the crevices of rock faces, around swamps and in moist forests. One of the most common ferns is bracken fern.

Coniferophyta – Conifers

Gymnosperms are the first group of vascular plants to produce seeds (see page 13). Unlike angiosperms (flowering plants), gymnosperms have uncovered seeds, hence their name – gymno, meaning “naked,” and sperm, meaning “seed.” The most common familiar phylum of gymnosperms is coniferophyta (conifers), which include pines, cedars, junipers, spruces and many others.

Conifers are woody and have cones and needles (in fact the needles are actually just long, pointed leaves!). They are also generally evergreen, meaning they do not lose their leaves/needles over the winter, but instead gradually replace them throughout their lifetime. Pine needles have a waxy coating, allowing them to retain water throughout the winter, while still allowing them to capture sunlight for photosynthesis. Conifers are mainly found in the northern hemisphere. They thrive in areas where summers are short and winters are long, due to their ability to retain water during the winter. They are also among the tallest trees, with some species growing upward of 90 meters!

Magnoliophyta – Flowering Plants

Flowering plants (angiosperms) in the phylum magnoliophyta are the most evolved, most diverse and most successful group of plants. In fact, flowering plants make up approximately 90 percent of the Kingdom Plantae! Angiosperms are vascular, seed-producing plants with flowers and fruits that enclose the seeds. Flowering plants have colonized nearly every land habitat conceivable – from deserts to windy alpine summits, marshes and rainforests. Flowering plants include grasses, lilies, roses, cacti and most broad-leaved trees.