Lepidodendron:-
1. Systematics:-
Division:- Lycophyta
Class:- Lycopsida
Order:- Lepidodendrales
Family:- Lepidodendraceae
Genus:- Lepidodendron
2. Habit and Habitat:-
> Lepidodendron also known as scale tree is an extinct genus of primitive, vascular, arborescent (tree-like) plant related to the lycopsids (club mosses).
> Luxuriant plant in nature.
> They sometimes reached heights of over 30 metres (100 ft), and the trunks were often over 1 m (3.3 ft) in diameter.
> They thrived during the Carboniferous Period (about 360 -300 million years ago) before going extinct.
> Sometimes erroneously called "giant club mosses", they were actually more closely related to today's quillworts than to modern club mosses.
> The name Lepidodendron comes from the Greek lepido, scale, and dendron, tree.
3. Study of sporophyte:-
> Lepidodendron had tall, thick trunks that rarely branched and were topped with a crown of bifurcating branches bearing clusters of leaves.
> These leaves were long and narrow, similar to large blades of grass, and were spirally-arranged.
> Spirally arranged branch scars were found on old stem.
> Dichotomous branching was found.
> The closely packed diamond-shaped leaf scars left on the trunk and stems as the plant grew provide some of the most interesting and common fossils in Carboniferous deposits. These fossils look much like tyre tracks or alligator skin.
> The scars, or leaf cushions, were composed of green photosynthetic tissue, evidenced by the cuticle covering and being dotted with stomata, microscopic pores through which carbon dioxide from the air diffuses into plants.
> Likewise, the trunks of Lepidodendron would have been green, unlike modern trees which have scaly, non-photosynthetic brown or gray bark.
> Lepidodendron has been likened to a giant herb.
> The trunks produced little wood, being mostly soft tissues.
> Most structural support came from a thick, bark-like region. This region remained around the trunk as a rigid layer that grew thicker, but did not flake off like that of most modern trees.
> As the tree grew, the leaf cushions expanded to accommodate the increasing width of the trunk.
> Acicular leaves:- Linear to lanceolate leaves are known as acicular leaves.
> Secondary growth:- There were 3 species based upon secondary growth:
i. L. pettycurranse (Normal secondary growth)
ii. L. rhodumnense (Secondary growth absent)
iii. L. vasculare (Medulation starts)
> Internal structure:-
i. Stem:- Exarch and eccentric condition was found in stem.
ii. Leaf:- Parichnous strands extending from leaf to root through stem. They perform the function of gaseous exchange in old stem and root, because lenticels were absent in old stem and roots.
4. Reproduction:-
> The branches of this plant ended in cone-structures.
> Lepidodendron did not produce true seeds like many modern plants. Instead, it reproduced by means of elaborate, encapsulated spores.
> It is estimated that these plants grew rapidly and lived 10–15 years.
> Most species were probably monocarpic, meaning they reproduced only once toward the end of their life.
> Fructification:- It is described under the name Lepidostrobus.
> Cylindrical cone:- Length = 10 - 12cm
Diameter = 1 - 2cm
5. Phylogeny:-
> Phylogeny:- The history of the evolution of a species or group, especially in reference to lines of descent and relationships among broad groups of organisms.
> By the Mesozoic era, the giant lycopsids had died out and were replaced by conifers as well as smaller quillworts.
> This may have been the result of competition from the emerging woody gymnosperms.
> Lepidodendron is one of the more common plant fossils found in Pennsylvanian-age (Late Carboniferous) rocks.
> They are closely related to other extinct lycopsid genera, Sigillaria and Lepidendropsis.
