This lifeform is found north of the Mason Dixon line in North America.

Alder buckthorn (Rhamnus alnifolia) is found from Quebec to British Colombia and south to New Jersey, Illinois, Nebraska, Wyoming, and California. This small shrub is found in swamps. The finely toothed leaves are somewhat oval and from two to four inches long. The flowers appear with the leaves, but have no petals.

Buckthorns (genus Rhamnus) comprise about 150 species of typically thorny trees found primarily in the Northern Hemisphere, but species are also known from Africa and Brazil.  This genus contains several native species of the United States  and two very undesirable Eurasian species.  Kartesz lists nine species and seven subspecies in his greater North America, which includes the United States, Canada, Hawaii, Greenland, Puerto Rico and the U.S. Virgin Islands.  (This genus is very close to the Frangula genus, and several species have migrated around.)

Buckthorn Family (Rhamnaceae) is a medium-sized family of woody  plants including vines, trees, and shrubs. There are perhaps 850 to 900 species in the family. There are 109 species arranged in 17 genera now growing in greater North America.

Rhamnales Order is a small order of woody plants containing only two families.

Dicots (Dicotyledoneae Class) are the predominant group of vascular plants on earth. With the exception of the grasses (Monocots) and the Conifers (Gymnosperms), most of the larger plants that one encounters are  Dicots. Dicots are characterized by having a seed with two outer shell coverings. Some of the more primitive Dicots are the typical hardwood trees (oaks, birches, hickories, etc). The more advanced Dicots include many of the Composite Family flowers like the  Dandelion, Aster, Thistles, and Sunflowers. Although many Monocots reach a very high degree of specialization, most botanists feel that the Dicots represent the most advanced group of plants.

Seed plants (Phylum Embryophyta) are generally grouped into one large phylum containing three major classes: the Gymnosperms, the Monocots, and the Dicots. (Some scientists separate the Gymnosperms into a separate phylum and refer to the remaining plants as flowering plants or Angiospermae.)

For North American counts of the number of species in each genus and family, the primary reference has been John T. Kartesz, author of A Synonymized Checklist of the Vascular Flora of the United States, Canada, and Greenland (1994). The geographical scope of his lists include, as part of greater North America, Hawaii, Alaska, Greenland, Puerto Rico, and the Virgin Islands.

Kartesz lists 21,757 species of vascular plants comprising the ferns, gymnosperms and flowering plants as being found in greater North America (including Alaska, Hawaii, Greenland, Puerto Rico and the Virgin Islands).

There are estimates within the scientific world that about half of the listed North American seed plants were originally native with the balance being comprised of Eurasian and tropical plants that have become established.

Plant kingdom contains a large variety of different organisms including mosses, ferns, and seed plants. Most plants manufacture their energy from sunlight and water. Identification of many species is difficult in that most individual plants have characteristics that have variables based on soil moisture, soil chemistry, and sunlight.

Because of the difficulty in learning and identifying different plant groups, specialists have emerged that study only a limited group of plants. These specialists revise the taxonomy and give us detailed descriptions and ranges of the various species.  Their results are published in technical journals and written with highly specialized words that apply to a specific group.

On the other hand, there are the nature publishers. These people and companies undertake the challenging task of trying to provide easy to use pictures and descriptions to identify those species.