Introduction to Lycophytes
History
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Lycophytes are the most primitive group of vascular plants extant.
The ancestors of these living, seedless vascular plants evolved during the Silurian Period.
By the Carboniferous Period there were two evolutionary lines: small herbaceous plants &
giant woody trees forming the first forests.
The trees lasted for millions of years in swamps but became extinct in the Permian Period
when the climate became drier.
The small herbaceous line survived and is today represented by the Lycophtyes.
Classification, Morphology and Life Cycles
Lycopophytes can be grouped in three families:
Lycopodiaceae (Club Mosses), Selaginellaceae (Spike Mosses), Isoetaceae (Quillworts).
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They are the most primitive group of vascular plants (tracheophytes).
The vascular tissue consists of xylem and phloem for transport.
They have roots that grow from distinct leafless branches or from small swollen structures at
the base of the stem; leaves (microphylls) that are small, spine shaped with a single vein
used for photosynthesis, as well as modified leaves bearing sporangia called sporophylls.
In some Lycopodiaceae sporophylls are clustered in dense cones.
Lycophytes have a reproductive cycle that involves an alternation of generations i.e.
sporophytes and gametophytes.
Sporophytes, which are small herbaceous plants, are the dominant generation.
The Lycopodiaceae like most seedless vascular plants, are homosporous producing one type
of spore that develops into a bisexual gametophyte.
The Selaginellaceae and Isoetaceae have two kinds of sporophylls: megasporangia producing
megaspores that develop into female gametophytes, and microsporangia producing
microspores that become male gametophytes.
The tiny, precursors (prothalli) of the gametophytes, sometimes are above ground (epigeal)
and photosynthetic, most remain underground (hypogeal) nourished by fungi.
The underground ones can lay dormant for seven years and can take fifteen years to reach
maturity and become a gametophyte. Vegetative replication can also occur.
Spores are released in clouds and are so rich in oil that dried spores of Huperzia selago were
ignited by magicians and photographers to create smoke, or flashes of light, with little heat
and were safe.
They generally occur in lake margins, wet lowland and upland bogs, moorlands, heaths and
mountains.
The commonest lycophyte species in Ireland are H. Selago and S. Selaginoides which are
locally frequent, but the other native species are considered rare and declining due to
habitat destruction.