Plants of Casa Grande Ruins National Monument - NPS Inventory ...

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The basics of plant systematics
The science of plant systematics organizes plants according to their evolutionary
relationships. In plant systematics, those relationships are characterized by the
unique traits of groups of plants, which are aggregated into what are known as
orders. Immediately below the order is the family, which is the organizational
foundation of this field guide. The order is the largest organizational category
and can consist of several to many different families.
The family is a grouping of related plants connected by some or several
specific characteristics. In systematics, some of these characteristics are called
synapomorphies, or character states that developed in the ancestors of the
family and can be found in all family members. For example, all plants in the
Mint Family, or Lamiaceae, have opposite leaves, square stems, and ethereal
oils that excrete the familiar minty smell.
Below the family level, each species has a Latin genera (or genus) name (e.g.,
Prosopis), followed by what is known as the specific (i.e., species) epithet (e.g.,
velutina). This way of organizing scientific names, known as the binomial
nomenclature system, dates to the 18th century and the Swedish naturalist
Carl Linnaeus. Although even generally accepted Latin names sometimes
have recognized alternatives (synonyms) and, as such, are subject to a limited
amount of regional variation, the Latin (or scientific) names are far more stable
than common names—which, especially relative to plants, are notoriously
unreliable.
The organization of plants in this guide is based on the Angiosperm Phylogeny
Group III (APG III), which the Sonoran Desert Network staff considers to be
the most recent and up-to-date plant systematics research. The Angiosperm
Phylogeny Group III provides guidance for current information about
relationships among plants and which genera are found in specific families.
For more information, visit the Angiosperm Phylogeny poster at http://www2.
biologie.fu-berlin.de/sysbot/poster/poster1.pdf. Further information about
plant systematics can also be found in the Works Cited section of this guide.