Classifying plants into Divisions, Classes, Subclasses, Orders, Families, Genus, Species, Subspecies and Cultivar makes it much easier to figure out what each plant wants and needs. If you can’t find information on the exact plant you have you can look for other closely related plants.
Plants are classified into three main groupings: nonvascular, vascular seedless, and vascular with seeds.
Non-vascular plants are the first ones to have left the oceans about 450 million years ago. They are the division of Bryophyta which includes the three classes: Musci, Hepaticae, and Anthocerotae. These plants can not stray far from water because they have no vascular system to carry the water to far reaches of the plant. The lack of a vascular system also keeps the size of these plants small. Musci has over 6000 species of mosses in it, mostly tropical. Hepaticae are your liverworts of which 8500 species are known to exist. Anthocerotae contains about 400 hornworts, a rather non descript family.
Vascular seedless plants began to appear about 430 million years ago. They include the divisions of Polypodiophyta, Psilophyta, Sphenophyta, and Lycophyta. Polypodiophyta contains about 12000 species of ferns. Psilophyta contains just a few species of whisk ferns which have niether leaves nor roots. Spehophyta contains your horsetail type plants, only about 40 species remain. Lychphyta are your club mosses of which we have about 1000 species.
Vascular seed plants were the last to evolve. They include Pinophyta, Cycadophyta, Ginkgophyta, Gnetophyta, and Magnoliophyta. Pineophyta are your conifers or cone bearing plants, 550 species remain with us today. Cycadophyta are your cycads only 100 species exist, and most of those in tropical areas. Ginkgophyta has only one surviving plant, Ginkgo biloba. Gnetophyta has 100 species of mostly desert plants. Magnoliophyta contains all the flowering plants which were the last to evolve and it contains the most species at about 400,000.
Magnoliophyta contains two classes: Magnoliopsida [dicots]( seedlings sprout with two leaves and complex vein patterns) and Liliopsida [monocots] ( seedlings sprout with one leaf which has parallel veins ). There are over 170,000 species in the magnoliopsida class. The liliopsida contains about 60,000 species of plants.
Magnoliopsida contains six subclasses: Asteridae, Caryophyllidae, Dilleniidae, Hamamelididae, Magnoliidae, Rosidae. Liliopsida contains five subclasses: Alismatidae, Arecidae, Commelinidae, Lilidae and Zingiberidae.
The USE Natural Resources Website has a nice tree of all the Kingdoms on down to species. If you are having trouble finding care information for a plant, try searching down that tree and see if you can find a closely related plant.