From Seed to Seed:
Plant Science for K-8 Educators

Families, Orders, Classes, Phylums, and Kingdoms

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 phylums. (Phylums are further classified into kingdoms; all plants are in one kingdom, Kingdom Plantae.)

Although plants are rarely referred to by their complete classification, 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 use nitrogen fixation to convert nitrogen to a form plants can use. So legume crops generally do not 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-peas or beans-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 is 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 contained in chloroplasts and show structural differentiation.

Phylum: Magnoliaphyta (formerly Anthophyta)-vascular plants 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.