BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

IX. LOWER SPORE PLANTS

Division Lycopodiophyta

Lycopods are Water/56.html">LOWER SPORE PLANTS in which the sporophyte is dominant over the gametophyte, with both the sporophyte and gametophyte being independent organisms.

The vegetative body of the sporophyte in modern lycopods is a perennial herbaceous plant consisting of dichotomously branched stems, adventitious roots, and phylloids. The stems are covered with an epidermis containing Stomata. A thick primary cortex lies beneath the epidermis. The central core consists of an axial vascular cylinder (protostele). It is composed of primary xylem formed by tracheids and phloem represented by very elongated Cells with sieve areas on their longitudinal walls. The subterranean PARTS OF THE shoots bearing spirally arranged roots are called rhizophores, and the leaves and roots are referred to as rhizomes.

Among fossil lycopods, quite massive trees (up to 30 m tall) were widespread, possessing the ability for secondary thickening of the stems and rhizophores due to the presence of a cambium.

Heterosporous lycopods possess a small outgrowth at the Base of the leaf, known as a ligule. The leaves are simple and entire, with 1-2 Veins.

The sporophyte leaves are differentiated into trophophylls (sterile leaves) and sporophylls, which bear sporangia on their upper surface. Sporophylls may alternate with trophophylls or aggregate at the SHOOT apices to form spore-bearing spikes, or strobili.

Spores within the sporangia can be morphologically and physiologically identical (homosporous plants) or differ in size and physiology (heterosporous plants), specifically being divided into small microspores and large megaspores.

The gametophytes of homosporous lycopods are bisexual and monoecious, ranging from 0.2 to 2 cm in size. They are subterranean or partially embedded in the soil, appearing as a thallus with rhizoids that form mycorrhizae with Fungi. Antheridia and archegonia are borne on the gametophyte. They exhibit a saprophytic or hemi-saprophytic lifestyle and take 1-15 years to mature.

In heterosporous lycopods, the gametophytes are unisexual, dioecious, and microscopic, developing entirely within the spore over the course of several weeks. The spermatozoa are biflagellate, except in Isoëtales, where they are multiflagellate. Fertilization is water-dependent. A sporophyte embryo develops from the zygote.

Lycopods originated from rhyniophytes during the Devonian period of the Paleozoic era. They reached their greatest diversification during the Carboniferous period. The vast majority of species went extinct by the end of the Paleozoic era.

The Division Lycopodiophyta comprises about 1,300 species and is divided into two classes: Lycopodiopsida and Isoëtopsida (quillworts). The flora of Ukraine includes 9 species of lycopods, of which only one species, lake quillwort (Isoëtes lacustris), is an aquatic plant.

Quillwort can occasionally form true underwater meadows on sandy, less frequently peaty or muddy substrates in the littoral zone of lakes, which serve as shelter for fish fry from predators.

Sporangia and spores that float to the water surface in autumn may be consumed by fish. The leaf tips are grazed by muskrats.