Plants provide nourishment for our bodies and minds. With the aid of protists and fungi, plants provide the oxygen we breathe and the food that sustains us—either directly or indirectly, by feeding other animals. Plants provide shade over our heads and cool carpets under our feet while surrounding us with beautiful colors and marking the change of seasons. Outstanding plants give us a grip on ecological communities.
Descriptions such as “Redwood-Tanoak Forest” or “Oak Grassland” indicate not only the plants we may find there but the animals, fungi, and climate as well. Categorization of the plant kingdom can be particularly confusing to the recreational naturalist. For example, according to modern botany:
- A palm tree has more in common with a blade of grass than with other trees.
- A strawberry plant is more closely related to an apple or apricot tree than to a clover or geranium.
- A Ginko (Maidenhair) tree is so different from other plants that it is in a phylum by itself. But if you have to group it with other plants, it belongs with conifers such as Pine trees.
At least four classification systems are in common usage: Plants are classified into 12 phyla or divisions based mostly on reproductive features; they are classified by tissue construction into non-vascular (mosses) and vascular plants (all others); by “seed” structure into those that reproduce through naked seeds, covered seeds, or spores; or by stature divided into mosses, ferns, shrubs and vines, trees, and herbs.
All of these higher-level groupings are undoubtedly lopsided: the vast majority of the 270,000 plant species are flowering herbs. The categories listed below provide slightly better balance: the largest phylum has been split while the other phyla are grouped according to one or more of the methods described above. Mosses and Allies (Bryophyta and Allies)
Mosses are non-vascular plants—they cannot transport fluids through their bodies. Instead, they must rely on surrounding moisture to do this job for them. Though small in stature, mosses are very important members of our ecosystem. They lay the foundations for other plant growth, prevent erosion, and contribute to the lush green appearance of many forested areas.
The 24,000 bryophyte species, sometimes grouped into a single phylum, are now grouped in three phyla: Mosses (Bryophyta), Liverworts (Hepatophyta), and Hornworts (Anthoceraphyta). They reproduce by spores, never have flowers, and can be found growing on the ground, on rocks, and on other plants.
Ferns and Allies (Pteridophyta and Allies): Ferns and Allies have a vascular system to transport fluids through their organic structures, but like the mosses, they reproduce from spores instead of seeds. The chief phylum, the Ferns (Filicinophyta = Pteridophyta), includes around 12,000 species.
Three other phyla are included as Fern Allies: the Horsetails (Sphenophyta = Equisetophyta, 40 species, right, accompanied by an orchid), Club mosses (Lycopodophyta, 1,000 species), and Whisk ferns (Psilophyta, 3 species).
Conifers and Allies (Gymnosperms = Coniferophyta and Allies): The gymnosperms add the following degree of complexity to plant development: they reproduce from seeds instead of spores. The seeds, however, are “naked” (Greek: gymnos) – not covered by an ovary.
Normally, the seed is produced inside a cone-like structure, such as a pine cone, hence the name “conifer.” Some conifers, such as the Yew and Ginkgo, produce their seeds inside a berry-like structure. Conifers are reasonably easy to identify: in addition to the aforementioned cones, these trees and bushes typically have needle-like, scale-like, or awl-like leaves. They never have flowers. Approximately 600 species are counted as conifers, including the pines, firs, spruces, cedars, retamas, and yew.
Species within the conifer ranks give us pine nuts – pesto’s magical ingredient – as well as retama berries for gin. Conifer Allies include three small phyla incorporating fewer than 200 species altogether: Ginkgo (Ginkophyta) with a single species, the Maidenhair Tree (Ginkgo biloba); palm-like Cycads (Cycadophyta); and herb-like cone-bearing plants (Gnetophyta) such as Ephedra.
Flowering Dicot Plants (Angiospermophyta, Class Dicotyledoneae): Angiosperms add the final improvement to plant reproduction: they grow their seeds inside an ovary (Greek: angeion = vessel) which is, itself, embedded in a flower.
After it is fertilized, the flower falls off and the ovary swells to become a fruit. Angiosperms in the class Dicotyledoneae grow two seed leaves (cotyledons). In addition, leaf leaves typically have a single, branching, main vein arising at the base of the leaf blade, or three or more main veins that diverge from the base. The vast majority of plants are dicots. Most trees, bushes, vines, and flowers belong to this group of around 200,000 species. Most fruits, vegetables, and legumes come from this class. (Angiospermophyta is also called Anthophyta or Magnoliophyta).
Blooming Monocot Plants (Angiospermophyta, Class Monocotyledonae) start with one seed-leaf. The chief veins of their leaf foliage are normally unbranching and almost parallel to each other. Around 30,000 plants are classified as liliopsids, including many of the prettiest members of kingdom Plantae: orchids, lilies, flags, palms, and even the Bird-of-Paradise plant.
The grasses which carpet our lawns and hayfields are also liliopsids. Monocots provide us with our primary sources of nutrition, giving us and the animals we eat grains such as wheat, oats, and maize, as well as fruits such as dates and bananas.