algae along with brown (Division Phaeophycophyta) and red algae
(Division Rhodophycophyta) are ancient groups that date back to
Archean time (over 3 billion yrs. ago). Masses of algal mats trap
sediments and have collectively been known as stromatolites.
Division BRYOPHYTA (the mosses,
hornworts, and liverworts)
They are the most primitive of green
plants and are not important in the geological record.
These are the vascular plants with
well developed conductive tissues which carry water and organic
PSYLOPHYTA (the psylophytes)
These are the earliest and most
primitive plants. They were small, one foot or less, branched,
seedless, and were not differentiated into roots, stems and leaves.
Some botanists separate the early fossil plants from the Psylophytes
and give them a separate subdivision, although this arrangement is
not followed here.
LYCOPODOPHYTA (the lycophytes)
group separated early into two major evolutionary lines. One
line, the club mosses remained grasslike. The other line, the
Lepidodendrales became one of the dominant forms in the coal forest
of the Carboniferous and became extinct at the end of the Permian.
Fossil trunks and roots show characteristic leaf and rootlet
SPHENOPHYTA (the sphenophytes)
record extends back to the Permian. This group also was an
important component of the Carboniferous coal forests, with some
members reaching over 50' in height. In general appearance
they resembled (except for size) the modern horsetail Equisetum.
The jointed trunk pattern seen in Calamites is characteristic
of the group.
FILICOPHYTA (the true ferns)
Although they are common members of
many floras they do not have great geological
SPERMATOPHYTA (the spermatophytes or seed plants)
The first four classes which follow
are often called the gymnosperms or plants with naked seeds.
PTERIDOSPERMOPHYTA (the pteridosperms)
pteridosperms are often referred to as seed ferns. These
plants have a fern-like foliage, but, in contrast to true ferns,
they bear seeds. They were the most common components of the
great coal forests of the Carboniferous.
CONIFEROPHYTA (conifers, pines, junipers, spruces, larches,
cypresses, and redwoods)
people are familiar with this class. Then, as now, they were
the largest and often the most common components of forests.
They were most common in the Mesozoic.
CYCADOPHYTA (the cycads)
cycads bear a superficial resemblance to palms. A common ornamental
cycad in the South (Cycas revolutus) is called a Sago
Palm. They were so common in the Mesozoic that this period of
time is often called the Age of Cycads. They were one of the
foods for herbivorous dinosaurs. They are much less common now.
GINKGOPHYTA (the ginkgoes or maidenhair trees)
Maidenhair trees were common in the
Mesozoic as a class, but are represented by only a single species
now. The leaf shape of this class is quite distinctive.
ANGIOSPERMOPHYTA (the flowering plants)
As the name indicates, they bear
flowers. They appear in Cretaceous time and their rapid
evolutionary rise has made them the dominant component of modern
floras. Their association with insects is essential. Some 65%
of flowering plants depend on insects for pollination and hence
reproduction. There are two subclasses of flowering plants:
monocots: palms, orchids, grasses and cereals
the dicots: which includes most broad leaf trees.