PLANT CLASSIFICATION BASICS
I. DIVISIONS OF THE PLANT KINGDOM
A. Spore-producing plants (Cryptogamia) include
ferns (Filices), horsetails (Equisetaceae), club mosses
(Lycopodiaceae), and mosses, scale mosses,
liverworts (Bryophyta)
B. Seed-producing plants: there are 2 basic groups or classes
1. Gymnosperms: include conifers, ginkgos, cycads
2. Angiosperms: flowering plants (plants which reproduce with stamens and
pistils)
The Angiosperms have 2 subclasses:
a) Monocotyledons
b) Dicotyledons
II.
Plants are classified according to their presumed evolutionary relationships, so
that those with a common ancestor are grouped together. In the flowering
plants, it is the structure of the flowers that most reliably shows these
relationships and enables us to figure out what is related to what. In a typical
dicot flower, there are 4 basic structures to the flower:
A. Calyx - composed of sepals - is the outer layer. It is usually green, but may
be colored and petal-like, e.g., Fuchsias.
B. Corolla - composed of petals, usually separate, but sometimes partially or
wholly fused to form a dish, cup, or tube. The corolla encloses the sexual
parts of the flower in a second layer.
C. Stamens - the male sexual part, consists of a stalk, called a filament, topped
by an anther, which produces the pollen.
D. Pistils - the female sexual part, consists of an ovary at the base (where the
seeds form following pollination), from which rises a stalk called the style,
topped by the stigma which is the receptacle for the pollen. The pollen grains
are conducted down the style to fertilize the ovary and make seeds.
However, there are many deviations from this plan. For instance, many
monocots lack the distinction between calyx and corolla. The two together are
called a perianth whose “petals" are called perianth-segments or tepals. The
stamens and pistils may be on separate flowers, with each plant being either
male or female (such plants are called dioecious). The stamens may come off
the pistil rather than be borne on their own stalks (e.g., Malvaceae). The petals
may be absent with the stamens taking over as the showy part of the flower
(e.g., bottlebrushes, etc.). The flowers may be grouped to imitate one large
flower (Asteraceae, Araceae) or they may be really weird like Euphorbiaceae.