lycopods or clubmosses (phylum Lycopodiophyta
lyco= wolf, pod=foot, phyt=plant or Lycophyta
"wolf plant") range from the Silurian to recent
times. Lycopods are not mosses. Clubmosses are more closely
and conifers (Kenrick & Davis, 2004, p. 32). Lycopods
are vascular plants with true roots, stems, and leaves.
leaves are spirally arranged with spore capsules in the
axes of leaves or arranged into terminal cones. Today,
species of small herbaceous clubmosses represent a small
fraction of modern flora, which possess an evolutionary
history rich in diversity and abundance extending back
The First Lycopods
Baragwanathia longifolia from the late Silurian
of Australia represents the earliest known lycopod. Baragwanthia was
a low-growing, herbaceous plant with simple Y-shaped
branching (Walker & Ward, 2002, p. 295). Stems had
a dense covering of leaves resembling tiny bristles or
hairs. The stems
of many lycopod plants may remind one of wolf paws. These
tiny bristles represent the earliest
examples of leaves in the fossil record (Kenrick & Davis,
2004, p. 34). Lycopods split into two major groups. One
group was herbaceous and has representatives in today's
The second group, the lepidodendrids, became woody and
treelike by the Late Devonian. Lycopods reached their
during the Carboniferous period and were among the dominant
plants of the wet, humid coal-forming forests (Raven & Evert,
1981, p. 320). The arborescent lycopods that dominated
forests became extinct as dryer conditions spread during
Alternation of Generations
Wet, humid environments are needed to complete the life
cycles of both nonvascular plants and spore producing
vascular plants. In the life cycle of plants a gametophyte
(haploid) generation alternates with a sporophyte (diploid)
generation. Seedless vascular plants such as lycopods,
sphenopsids, and ferns possess structures that produce
spores dispersed by wind. These spores are more drought-resistant
than the non-vascular plants like mosses and liverwarts.
The spores grow into small, inconspicuous gametophyte
plants that possess one set of genetic instructions (haploid).
Gametophyte plants have structures that produce sperm
or eggs. Water is required for the sperm to swim to and
fertilize eggs, forming zygotes. Zygotes with two sets
of genetic instructions grow into the large sporophyte
plants. The sporophyte plant will once again produce
spores continuing the alternation of generations.
Lycopods (Lycophyta) represented the dominant tree form
during the Carboniferous. Lepidodendron was
a lycopsid that could reach a height of
30 m and a width of 1m near its base. Lepidodendron leaves
did not have a petiole and grew directly from the stem.
Leaves were triangular in cross-section and arranged
spirals. The leaves of Lepidodendron are known
The needle-like leaves were clustered around spore-bearing
at the end of branches (Janssen, 1979, p. 36). When leaves
scar was left behind (Willis, McElwain & Curtis,
2002, p. 102). The trunk
was tapering and pole-like, studded with the diamond-shaped
leaf scars, graced
with a crown of bifurcating branches atop. In cross-section,
the arborescent clubmoss trunk was composed of a small
inner woody ring surrounding central pith. A soft layer
of living primary bark and phelloderm tissue encased
the woody inner ring. The exterior was covered with a
hard lignified, non-water
conducting, layer provided strength.
The bark layer accounted for up to 98% of the trunks
diameter, making the term "bark stem" appropriate for
these trees (Selmeier, 1996, p. 139). Trunks of this
type are prone to buckling at branching points.
at small angles. Overall, branching is sparse
in the tree design (Kenrick & Davis, 2004, p. 70).
or more radiating "arms",
extensively branched, spread into the substrate in a
are referred to as Stigmaria and had spirally
arranged lateral appendages or roots. When these appendages
shed a circular scar was left behind. Sigillaria was
similar to Lepidodendron, but exhibits a different
leaf scar pattern
on its bark, did not
tend to branch, and bore cones at the end of stems
erupting from the trunk (Janssen, 1979, p. 54). Both
were fast growing and had trunks with soft inner tissues
surrounded by a protective layer of bark. These trees
tissue in the bark, stems, and leaves.
Multiple Names for One Organism
Parts of the Lepidodendron tree were discovered and named
before their relationships were fully understood. The diamond-studded
stem is named Lepidodendron, the roots Stigmaria,
the leaves Lepidophyllum, and the reproductive structures Lepidostrobus (Janssen,
1979, pp, 35-68).
Science Olympiad Fossil Event
The 2016 Science Olympiad Fossil List includes the genus Lepidodendron (scale tree) within the phylum Lycopodiophyta.
6 cm x 5 cm
Lepidodendron Root Structure
17.5 cm x 9 cm
Black & White Mine, Gadbury Brick Works, Atherton, near
Wigan, Lancashire, UK
Westphalian B (Duckmantian); Upper Carboniferous
5.5 cm x 3.5 cm
Plate is 19 cm x 7 cm
Upper Carboniferous, Westfalien
Smaller Cone 4.5 cm in length
Kladno, Czech Republic
Plate is 21 cm x 16 cm
Upper Carboniferous; Westfalien
Lieg, Luik, Belgium
6 cm x 8 cm shown
R.E. (1979). Leaves and Stems from Fossil Forests:
A Handbook of the Paleobotanical Collections in the
Illinois State Museum. Springfield, Illinois:
Illinois State Museum.
Kenrick, P. and Davis, P. (2004). Fossil Plants. Smithsonian Books:
Raven, P.H., Evert, R.F., & Curtis, H. (1981). Biology of Plants [3rd
Ed]. New York: Worth Publishers, Inc.
A. (1996). Identification of Petrified Wood Made Easy. In Dernbach,
U. Petrified Forest: The World's 31 Most Beautiful Petrified
Forests (pp. 136-147). Germany:
C. & Ward, D. (2002). Smithsonian Handbooks: Fossils.
New York: Dorling Kindersley
K.J. & McElwain, J.C. (2002). The Evolution of Plants.
New York: Oxford University Press.