Describe the Structure of a Moss Plant

Written by beth asher
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Introduction
  • Introduction

    Describe the Structure of a Moss Plant

    Mosses are bryophytes, primitive plants believed to be among the first to develop the ability to live on land. Mosses have no vascular tubes to transfer water or nutrients, and no true stems or roots. Environmental water sources and absorption limit their size. The University of Massachusetts estimates there are 14,500 moss species growing in different habitats, all having basically the same structure.

    Simple mosses are among the original land plants (Moss image by Yaroslav Knish from Fotolia.com)

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    Basic Spores

    The initial moss plant is a spore given off by the sporophyte that forms at the end of the moss plant's "stem." Released spores travel long distances on the wind and remain viable for decades. Spores landing in suitable conditions divide and produce hairy filaments called protonemas, which weave across the growing medium. Sprouting from the spore filaments, gametophytes form, held to the surface by rhizoids.

    Sporophytes produce hundreds of spores (flowering moss image by lugome from Fotolia.com)

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    Main Structure

    The main moss structure is the gametophyte, a moss's "stem" and "leaves." A moss stem (called the axis) supports leaflike structures (phyllids) that carry out photosynthesis, transforming sunlight into sugars the moss uses for food. Typically arranged in a spiral, moss "leaves" are usually one cell thick with ribs two or more cells thick down their centres. Moss stems end in root-like strands called rhizoids, specialised to hold the moss to its growing surface.

    Mosses have no true leaves (Plant (moss) image by Eugen from Fotolia.com)

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    Second-Generation Growth

    The second moss structure is really a second generation. Moss plants reproduce sexually using separate plants produced at different times. This is indicated in the name endings. "The termination '-phyte' means 'plant,' so the gametophyte is the 'gamete plant' and the sporophyte is the 'spore plant,'" Heino Lepp of the Australian National Botanic Garden reports in his article, "What is a Bryophyte?" Gametophytes are tipped with either inverted cone-shaped areas (archegonia) or male reproductive organs (antheridia). Released sperm (antherizoids) need water since they swim to the archegonium. Sprouting from the gametophyte tip after fertilisation, a sporophyte holds itself in place by anchoring a foot in the archegonium.

    Sporophytes growing from gametophytes (moss image by Alison Bowden from Fotolia.com)

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    Spore-Bearing Parts

    The sporophyte stalk, called the seta, bears the sporangium (spore capsule) on its tip. One sporangium may produce up to a million spores. Maturing spore capsules are guarded by a covering called the calyptra that shrivels and falls off when the spores are mature. A cap called the operculum tops the capsule's opening under the calyptra. The capsule opening (peristome) can have teeth that help hold it closed. Matured spores are released when the capsule top ruptures and drift off to form new plants.

    Sporangia held aloft by the seta (moss - macro shot image by Jaroslav Machacek from Fotolia.com)

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    Asexual Reproductive Parts

    Mosses don't depend on only sexual reproduction. Gametophytes have balls of unspecialised cells, called gemmae, attached to them. If broken off each, simple cell can bud to form a protonema that sends out lateral shoots. New gametophytes develop from the shoots, ensuring the moss's survival. Their simple structure and multiple reproductive methods allow mosses to thrive from the Arctic Circle to the equator.

    One protonema produces many shoots (green moss image by Furan from Fotolia.com)

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