ARBORESCENT LYCOPODS PRIMITIVE PTERIDOPHYTES

PRIMTIVE PTERIDOPHYTA

1. ARBORESCENT LYCOPODS Submitted to: Submitted By: Dr. Pratap Srivastava Vivek Kumar M.Sc. Sem-1 Department of Botany University of Allahabad

2. INTRODUCTION: All the modern living Lycopods are herbaceous plants but their Palaeozoic relatives were herbaceous as well as large trees (Arborescent). Arborescent lycopods are fossils pteridophytes which were tree like. They were abundant in the Palaeozoic coal swamps and were an ecological keystone taxa of this important biome. Reconstruction of Lepidodendron

3. Arborescent lycopods dominated land during the Carboniferous period, which lasted about 60 million years. Arborescent lycopods evolved from Zosterophyllum during the Palaeozoic era. The evolution pathway of lycopods is: Chlorophyte ancestors -> Tracheophyte ancestors -> Zosterophyllum -> Arborescent lycopods -> Herbaceous lycopods. Lepidodendron, Stigmaria and Sigillaria are the best examples of arborescent lycopods

4. LEPIDODENDRALES: These were big trees with a height of 30 m or more and a diameter of about 2 m at the base They were trees of moist and swampy areas Appeared on the Earth during the upper Devonian period Extreme abundance during carboniferous period Started declining during early Permian and became extinct by the end of Permian period as the climate became drier in the late Pennsylvanian and Permian.

5. The two most common genera of lepidodendrales found in Pennsylvanian rocks are Lepidodendron and Sigillaria Lepidodendron is the form-genus for impressions of the outer bark of large arborescent lycophytes Lepidodendron grew to over 30m tall and preferred the wetter, areas in swamps Lepidodendron is recognized by the diamond-shaped pattern of leaf scars, each scar being generally longer than wide. Lepidodendron also called ‘scale tree’ They had long grass like leaves and reproductive cones

6. Wood Anatomy: In most species, secondary growth is characteristic of the genus It was initiated by the unifacial activity of the cambium. Only secondary xylem was produced externally and the cambium did not produce secondary phloem. There was massive extrastellar secondary growth by the meristematic activity of cortical parenchyma.

7. Sporophylls: The sporophylls were helically attached to the central cone axis. The microsporophylls bearing microsporangia usually borne in the apical portion Megasporophylls bearing megasporangia occupied the basal portion of the cones. Hence Lepidodendron was heterosporous The strobili was described as Lepidostrobus and Lepidocarpon (megasporangiate cones)

8. According to Phillips (1979) the entire structure was shed like a seed after development of embryo Ovules and seed had not been reported, due to this it cannot be considered as a true seed rather it is a false seed or a seed like structure. L.S. of cone of Lepidodendron

9. Sigillaria stems have somewhat rounded leaf scars that are arranged spirally, but vertical ridges between the scars give the appearance that the scars are in vertical rows Stigmaria was a large trunk base that divided dichotomously into four large massive descending axes. The Stigmaria spread over an area of about 20 ft (6 m) across.

10. Bark of Sigillaria Bark of Lepododendron Reconstruction of Lepidodendron

11. Reconstruction of Sigillaria Stump cast of Stigmaria Reconstruction of Stigmaria