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

VI. SYSTEM OF THE PLANT WORLD

LOWER SPORE PLANTS

GENERAL CHARACTERISTICS AND FEATURES

Order Fucales - Fucales

It unites Algae of complex tissue Structure, with flat-ribbon-like or cylindrical, broadly branched thalli that have a short stipe and are attached to the substrate by a holdfast. They are characterized by apical growth, an oogamous (exceptionally heterogamous) sexual process, and a diplontic life cycle without Morphology/12.html">ALTERNATION OF GENERATIONS (although some believe these algae possess a haplo-diplontic cycle with sporic reduction and a heteromorphic alternation of generations).

The sex Organs are located in depressions of the cortex and intermediate tissue — conceptacles or scaphiids, where both types of Gametes are formed, or only female or male ones, and they can be located on the same thallus or different ones. From 1 to 8 oospheres develop in the oogonia, and 64 spermatozoa in each antheridium.

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Fig. 22. Development cycle of Laminaria saccharina:

1 - sporophyte, 2 - zoosporangia, 3 - zoospores,

4 - gametophyte, 5 - antheridium, 6 - oogonia, 7 — spermatozoa

A distinctive feature of the spermatozoa is the presence of an apical thickening (proboscis) and a posterior flagellum longer than the anterior one. The oosphere releases the pheromone fucoserratine. Asexual reproduction is absent.

Representatives of the order include the genera Fucus, Cystoseira, Sargassum, Ascophyllum, Hormosira, etc.

The genus *Fucus* is very common in the littoral zone of northern (rarely temperate) seas, and is distinguished by flat, dichotomously branched thalli up to 2 m long, with a longitudinal rib (midrib) on the "branches" and apical growth of the thallus, which is attached to the substrate by a disc-shaped holdfast. Often, air bladders (vesicles) develop on the sides of the midrib, which help maintain the vertical position of the thallus in the water, especially during low tide.

Fig. 23. General appearance of the sporophyte and Structural Features of Fucus vesiculosus:

A - general view of the thallus (1 - air bladders, 2 - receptacles), B - section through a male scaphiid,

C - section through a female scaphiid, D - branchlet with antheridia, E - oogonium, F, G - release of the oosphere, H - release of spermatozoa

Sex organs develop on special fertile "branchlets" — receptacles, which form conceptacles or scaphiids, the cavities where they reside. The latter are filled with mucus, and the inner lining layer of Cells gives rise to sterile filaments and reproductive cells that form male and female sex organs in the same or different scaphiids (monoecious or dioecious conditions). During The formation of sex organs, the Nucleus of the initial Cell undergoes meiotic division, producing haploid cells from which oogonia or antheridia develop. The oogonium, in the form of large oval cells, has a unicellular stalk and 8 oospheres, as well as Hair-like cells — paraphyses, which often protrude from the opening of the conceptacles. The antheridium contains 64 biflagellate spermatozoa. The oospheres produce the pheromone fucoserratine, which facilitates the rapid attraction of male gametes and their Fertilization in the aquatic environment. The zygote grows into a new diploid sporophyte without a resting period.

Used for The production of fodder meal and alginates.

The genus *Cystoseira* includes very common macroscopic (up to 2 m) shrub-like, monopodially branched algae with ascending cylindrical "branches" and short "stipes", attached to a rocky substrate. These algae grow at a depth of 1–4 m in southern seas, particularly in the Black Sea. An anatomical feature of the genus is the dense type of core formed by tightly packed rows of cells. The oogonia contain only a single oosphere. They are one of the main producers of phytomass in benthic phytocoenoses of the littoral zone.