Paleozoic Life History - The Changing Earth: Exploring Geology and Evolution - page 588

It is evident from the fossil record that whereas the Early
Carboniferous fl ora was similar to its Late Devonian coun-
terpart, a great deal of evolutionary experimentation was
taking place that would lead to the highly successful Late
Paleozoic flora of the coal swamps and adjacent habitats.
Among the seedless vascular plants, the lycopsids and sphe-
nopsids were the most important coal-forming groups of the
Pennsylvanian Period.
The lycopsids were present during the Devonian,
chiefl y as small plants, but by the Pennsylvanian, they were
the dominant element of the coal swamps, achieving heights
up to 30 m in such genera as Lepidodendron and Sigillaria .
The Pennsylvanian lycopsid trees are interesting because
they lacked branches except at their top, which had elon-
gate leaves similar to the individual palm leaf of today. As
the trees grew, the leaves were replaced from the top, leav-
ing prominent and characteristic rows or spirals of scars on
the trunk. Today, the lycopsids are represented by small
temperate-forest ground pines.
The sphenopsids, the other important coal-forming
plant group, are characterized by being jointed and hav-
ing horizontal underground stem-bearing roots. Many of
these plants, such as Calamites , average 5 to 6 m tall. Living

sphenopsids include the horsetail ( Equisetum ) or scouring
rushes (

Figure 21.35). Small seedless vascular plants and
seed ferns formed a thick undergrowth or ground cover be-
neath these treelike plants.
Not all plants were restricted to the coal-forming
swamps. Among those plants that occupied higher and
drier ground were some of the cordaites , a group of tall
gymnosperm trees that grew up to 50 m high and prob-
ably formed vast forests (

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Figure 21.36). Another impor-
tant nonswamp dweller was Glossopteris , the famous plant
so abundant in Gondwana (see Figure 2.1), whose distri-
bution is cited as critical evidence that the continents have
moved through time.
The floras that were abundant during the Pennsylva-
nian persisted into the Permian, but because of climatic
and geologic changes resulting from tectonic events, they
declined in abundance and importance. By the end of the
Permian, the cordaites became extinct, and the lycopsids
and sphenopsids were reduced to mostly small, creep-
ing forms. Gymnosperms with lifestyles more suited to
the warmer and drier Permian climates diversified and
came to dominate the Permian, Triassic, and Jurassic
landscapes.

◗

◗

Figure 21.36 Late Carboniferous Cordaite Forest Cordaites were
a group of gymnosperm trees that grew up to 50 m tall.

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Figure 21.35 Horsetail Equisetum Living sphenopsids include
the horsetail Equisetum .