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Plants in the Lycophyta have erect stems as well as Stolons and Rhizomes. They are relatively large compared to Hepatophyta, Bryophyta and Psilophyta but they rarely exceed a meter in height. They can be epiphytic and pendant stems can be more than a meter in length. They have Microphylls and Roots. Branching is Dichotomous for both organs. The Apical Meristem has several "Initials" rather than a solitary Apical Cell.

We will examine the genus Lycopodium first.

LycoHuperziaSAMSEMLab.jpg (73888 bytes)
SEM photo of a Lycopod SAM
LycApicalMeriLab400.jpg (102896 bytes)
Long Section of a Lycopod SAM: Note the presence of several large "Initials" at the summit of the stem.

These plants are most abundant in the tropics but a few can survive cold, dry environments.

LYCWholDrawBIODBLab400.jpg (144116 bytes)
A composite Lycopodium
LycoJasper.jpg (141267 bytes)
A species growing in the Arctic/Alpine zone near Jasper Canada. This plant is approx. 10 cm in length.
LycoIsoDichoPlant.jpg (12979 bytes)
Vertical Lycopodium with Isotomous Branching. This plant is about 15-20 cm tall.
LycoPRPendant.jpg (95683 bytes)

A Pendant Epiphytic Lycopodium from Puerto Rico. note the Dichotomous Branching. This plant is over 1 m in length.

LycoLocalIsotBranch.jpg (108091 bytes)
A local Lycopodium showing Isotomous Branching and well developed Microphylls.
LycoRootStemBascLab200.jpg (51981 bytes)
Lycopodium lucidulum: Note the Vertical Stem. The Roots are adventitous and originate in the stem. They branch Dichotomously.
LycoShooTipCrop.jpg (121534 bytes)
Shoot tip of L. lucidulum:
Microphylls Galore!!!!
LycoRootStemBaseLab300Crop.jpg (44109 bytes)
Roots from the image above: Note the Dichotomous Branching.
LycoLeafX-sLab400.jpg (111689 bytes)
Cross section of a Lycopodium Microphyll
: Note the uniform (unspecialized) Mesophyll and the Cuticle.
Stomata are visible on the upper side of the leaf.

The species to the right grows locally on disturbed sites and could be a candidate for soil stabilization research. It is a complex plant which has horizontal Stolons which have Isotomous Branching. These produce the Roots which anchor the plant to the substrate. The Stolons also produce Aerial Shoots which have Anisotomous (unequal) branching. The upright stems are about 1 m in height.

LycoHawComplxPlantLab200.jpg (85566 bytes)
LycoHaploStele.jpg (126124 bytes)
Simple Stele from a Lycopod Root.

Cross section of a Lycopodium Rhizome: LycoRhizomeLab.jpg (156948 bytes)The Stele is more complex than that of the Root above.

Bands of Xylem are surrounded by Phloem. Note the extensive Sclerenchyma in the Ground Tissue.

Cross section of L. lucidulum Aerial Stem:LycoStemX-SPhGlucTolBlueLab.jpg (129832 bytes) The Cortex contains Parenchyma.

The Xylem (stained blue) is prominent in the Stele.

Stele from a Lycopodium Stem: The XylemLycoPlectoRealSteleLab.jpg (227314 bytes) resembles sheets or flaps. Each arm is surrounded by Phloem. This is called a Plectostele (Plecto = Plate). This is more complex that the stele in Psilotum. The Leaf Traces are small Vascular Bundles which diverge from the central stele and connect with the vein in the leaf. This produces an integrated vascular system that include the three major vegetative organs.

LepidodendronTreeLab.jpg (28378 bytes)

While extant Lycopods are small plants with little ecological significance. Forests of tree-sized lycopods once dominated certain  habitats. The most famous of these is Lepidodendron which reached heights up to 30 meters. They had secondary growth. The stems were coated with leaf bases and there appeared to be little internodal elongation. The latter implies that the trees had slow growth which may partly account for their extinction.

LepidoBase.jpg (67839 bytes)
Lepidodendron Stem Base
LepidoLeafScarsLab.jpg (68750 bytes)

The next major step in evolution was the development of a complex leaf called a Megaphyll.

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