Gardeners frequently speak in terms of genus and species,
occasionally speak of a plant’s family,
and rarely mention the more inclusive groupings—order,
class, and division.
As we said earlier, botanists and taxonomists
grouped species into genera (plural of genus) based on plant characteristics and perceived
relationships. They continued with this grouping—still based on unifying
characteristics—and formed more and more inclusive categories. Genera are grouped
into families, families into orders, orders into classes, and, finally, classes into
divisions. (Divisions are further classified into kingdoms; all plants are in one kingdom,
Kingdom Plantae.)
Backyard gardeners needn’t know a plant’s
complete classification, but it is sometimes helpful to know what family a plant belongs
to. For example, the family Leguminosae, commonly called the pea family, contains plants
that form a symbiotic relationship with rhizobium bacteria, and in doing so are able to
fix atmospheric nitrogen and convert it to a form plants can use. So legume crops
generally don’t require heavy nitrogen fertilization. Knowing this means you’ll
save on fertilizer, and you’ll understand why it’s helpful to rotate a legume
crop with a crop like corn that requires lots of nitrogen for good growth.
To give you an idea of both the complexity and the logic
of the system of classification, here’s the complete classification for corn,
starting from the most inclusive grouping, the plant kingdom, and working down to the most
specific, the species.
Kingdom: Plantae—organisms that have
chlorophyll a and b contained in chloroplasts and show structural differentiation
Division: Magnoliaphyta (formerly
Anthophyta)—vascular plant with seeds and flowers; ovules enclosed in an ovary (the
angiosperms)
Class: Magnoliopsida (formerly
Monocotyledones)—embryo with one cotyledon; flower parts usually in threes, stem with
scattered vascular bundles
Order: Poales (formerly
Commelinales)—monocots with fibrous leaves, reduction and fusion in flower parts
Family: Poaceae—hollow-stemmed
monocots with reduced flowers, fruit a caryopsis; the grasses
Genus: Zea—robust grasses
with separate staminate and carpellate flower clusters; caryopsis fleshy
Species: Zea mays—corn
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 Mum's
the word Gardeners are sometimes frustrated
by conflicting nomenclature. For example, you might expect to find the common
florists’ mum or garden mum in the genus Chrysanthemum. And it used to
be found there. But this genus has recently been split into several groups, and the
familiar mum is now classified as Dendranthema grandiflorum.
Though using scientific names is certainly
more precise than using common names, we must remember that these scientific names are not
set in stone. Periodically, a botanist will discover something about a plant that changes
the current thinking about that plant’s likely evolutionary history. The result is
that a plant classified in one genus is discovered to be more closely related to another
group of plants. Though frustrating for gardeners and botanists alike, it must be
remembered that taxonomy, the classification of organisms, is a "living"
science, subject to periodic review and modification. |
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