Introduction:
Based on the flowering plants are classified into 2 types.
1. Cryptogams
2. Phenerogams
Cryptogams:
A cryptogam is a plant that reproduces by spores, without flowers or seeds. "Cryptogamae" means hidden reproduction, referring to the fact that no seed is produced, thus cryptogams represent the non-seed bearing plants.
Cryptogams are classified into 3 groups.
i. Thallophyta
ii. Bryophyta
iii. Pteridophytes
i. Thallophyta:
The thallophytes are a polyphyletic group of non-mobile organisms traditionally described as "thalloid plants", "relatively simple plants" or "lower plants". They were a defunct division of Kingdom Plantae that included fungus, lichens and algae and occasionally bryophytes, bacteria and the Myxomycota. They have a hidden reproductive system and hence they are also called Cryptogamae (together with ferns), as opposed to Phanerogamae. The thallophytes are defined as having undifferentiated bodies (thalli), as opposed to cormophytes (Cormophyta) with roots and stems.
It has two types of plants.
a. Algae
b. Fungi
a. Algae:
The word algae represent a large group of different organisms from different phylogenetic groups, representing many taxonomic divisions. In general algae can be referred to as plant-like organisms that are usually photosynthetic and aquatic, but do not have true roots, stems, leaves, vascular tissue and have simple reproductive structures.
They are distributed worldwide in the sea, in freshwater and in wastewater. Most are microscopic, but some are quite large, e.g. some marine seaweeds that can exceed 50 m in length.
The unicellular forms are known as microalgae. Microalgae comprise a vast group of photosynthetic, heterotrophic organisms which have an extraordinary potential for cultivation as energy crops. They can be cultivated under difficult agro-climatic conditions and are able to produce a wide range of commercially interesting byproducts such as fats, oils, sugars and functional bioactive compounds.
Seaweed is a loose colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae. They are photosynthetic, like plants, and "simple" because they lack the many distinct organs found in land plants. For that reason they are currently excluded from being considered plants.
The algae have chlorophyll and can manufacture their own food through the process of photosynthesis. Almost all the algae are eukaryotes and conduct photosynthesis within membrane bound structure called chloroplasts. Cyanobacteria are organisms traditionally included among the algae, but they have a prokaryotic cell structure.
Algae produce oil, and because of their growth rate and yields, they could produce a lot more than other energy crops. Some estimates suggest that microalgae are capable of producing up to 15,000 gallons of oil per Hectare a year. This could be converted into fuels, chemicals and more.
Algae are divided into subgroups. Those are....
Green Algae:
The "green algae" is the most diverse group of algae, with more than 7000 species growing in a variety of habitats. The "green algae" is a paraphyletic group because it excludes the Plantae. Like the plants, the green algae contain two forms of chlorophyll, which they use to capture light energy to fuel the manufacture of sugars, but unlike plants they are primarily aquatic. Because they are aquatic and manufacture their own food, these organisms are called "algae," along with certain members of the Chromista, the Rhodophyta, and photosynthetic bacteria, even though they do not share a close relationship with any of these groups.
Uses of Green Algae:
* Microscopic green algae are nutritious like higher plants, because they contain vitamins, minerals and organic material. However, they are not necessarily palatable like higher plants.
* Some forms of green algae (Chlorella) are grown in mass culture, dried and made into tablets for consumption as a food supplement. However, caution is advised due to an excess of nucleic acids, which can have adverse effects.
* Green algae have been promoted as potential bio-fuels, because they can produce and store oils. With the volatile oil production market and concerns about rising carbon dioxide levels associated with climate change, the development of bio-fuels is creating more interest among politicians and is more attractive for investors. Presently, the use of algae for bio-fuels is not economically feasible and extensive research must be conducted to demonstrate the technological practicality.
Red Algae:
Red algae are red because of the presence of the pigment phycoerythrin; this pigment reflects red light and absorbs blue light. Because blue light penetrates water to a greater depth than light of longer wavelengths, these pigments allow red algae to photosynthesize and live at somewhat greater depths than most other "algae". Some rhodophytes have very little phycoerythrin, and may appear green or bluish from the chlorophyll and other pigments present in them.
In Asia, rhodophytes are important sources of food, such as nori. The high vitamin and protein content of this food makes it attractive, as does the relative simplicity of cultivation, which began in Japan more than 300 years ago. Some rhodophytes are also important in the formation of tropical reefs, an activity with which they have been involved for millions of years; in some Pacific atolls, red algae have contributed far more to reef structure than other organisms, even more than corals. These reef-building rhodophytes are called coralline algae, because they secrete a hard shell of carbonate around themselves, in much the same way that corals do.
Brown Algae:
The Phaeophyceae or brown algae is a large group of mostly marine multicellular algae, including many seaweeds of colder Northern Hemisphere waters. They play an important role in marine environments, both as food and for the habitats they form. For instance Macrocystis, a kelp of the order Laminariales, may reach 60 m. in length, and forms prominent underwater forests. Another example is Sargassum, which creates unique habitats in the tropical waters of the Sargasso Sea. Many brown algae, such as members of the order Fucales, commonly grow along rocky seashores. Some members of the class, such as kelp, are used as food for humans.
Worldwide there are about 1500 – 2000 species of brown algae. Some species are of sufficient commercial importance, such as Ascophyllum nodosum, that they have become subjects of extensive research in their own right.
Brown algae belong to a very large group, the Heterokontophyta, a eukaryotic group of organisms distinguished most prominently by having chloroplasts surrounded by four membranes, suggesting an origin from a symbiotic relationship between a basal eukaryote and another eukaryotic organism. Most brown algae contain the pigment fucoxanthin, which is responsible for the distinctive greenish-brown color that gives them their name. Brown algae are unique among heterokonts in developing into multicellular forms with differentiated tissues, but they reproduce by means of flagellated spores and gametes that closely resemble cells of other heterokonts. Genetic studies show their closest relatives to be the yellow-green algae.
Phytoplankton:
Phytoplanktons are the autotrophic components of the plankton community and a key factor of oceans, seas and freshwater basin ecosystems. Most phytoplankton are too small to be individually seen with the unaided eye. However, when present in high enough numbers, some varieties may be noticeable as colored patches on the water surface due to the presence of chlorophyll within their cells and accessory pigments such as phycobiliproteins, xanthophylls, etc. in some species.
Blue Green Algae:
Blue-green algae, also known as Cyanobacteria, are a group of photosynthetic bacteria that many people refer to as "pond scum." Blue-green algae are most often blue-green in color, but can also be blue, green, reddish-purple, or brown. Blue-green algae generally grow in lakes, ponds, and slow-moving streams when the water is warm and enriched with nutrients like phosphorus or nitrogen.
When environmental conditions are just right, blue-green algae can grow very quickly in number. Most species are buoyant and will float to the surface, where they form scum layers or floating mats. When this happens, we call this a "blue-green algae bloom." In Wisconsin, blue-green algae blooms generally occur between mid-June and late September, although in rare instances, blooms have been observed in winter, even under the ice.
Many different species of blue-green algae occur in Wisconsin waters, but the most commonly detected include Anabaena sp., Aphanizomenon sp., Microcystis sp., and Planktothrix sp. It is not always the same species that blooms in a given waterbody, and the dominant species present can change over the course of the season.
b. Fungi:
A fungus is a eukaryote that digests food externally and absorbs nutrients directly through its cell walls. Most fungi reproduce by spores and have a body (thallus) composed of microscopic tubular cells called hyphae. Fungi are heterotrophs and, like animals, obtain their carbon and energy from other organisms. Some fungi obtain their nutrients from a living host (plant or animal) and are called biotrophs; others obtain their nutrients from dead plants or animals and are called saprotrophs (saprophytes, saprobes). Some fungi infect a living host, but kill host cells in order to obtain their nutrients; these are called necrotrophs.
Study of Fungi Mycology. Father of Fungi is Mycali. The fungi include several thousand species of eukaryotic, sporebearing organisms that obtain simple organic compounds by absorption. The organisms have no chlorophyll and reproduce by both sexual and asexual means. The fungi are usually filamentous, and their cell walls have chitin. The study of fungi is called mycology, and fungal diseases are called mycoses.
Together with bacteria, fungi are the major decomposers of organic materials in the soil. They degrade complex organic matter into simple organic and inorganic compounds. In doing so, they help recycle carbon, nitrogen, phosphorous, and other elements for reuse by other organisms. Fungi also cause many plant diseases and several human diseases.
Characteristics of Fungi:
* Fungi cannot make their own food like plants. They are heterotrophs and depend upon other organism for their carbon source.
* Organisms that derives their nutrition from the protoplasm of another organism.
* Organisms that obtains their carbon source from the by-products of organisms or dead organisms. However, if the opportunity arises, some saprobes may become parasitic. Such organisms are said to be facultative parasites.
* In the strict sense, this term refers to the habitual "living together" of different species. As such, there are a number of different categories of relationships that may fit under this term. However, we will define it in its most common usage: "The intimate association of two dissimilar organisms in a mutually beneficial relationship, e.g. lichens and mycorrhizae." This type of symbiosis is specifically referred to as a mutualistic symbiosis.
* Fungi have membrane bound organelles, i.e. nucleus, mitochondrion, E.R., etc. Once upon a time filamentous bacteria called Actinomycetes were classified with fungi, but this is no longer the case.
* The assimilative stage of the fungal body, i.e. mycelium or yeast, has a cell wall. In the strict sense organisms classifies as fungi have cell walls composed primarily of chitin. However, we will be also be covering "fungi" that do not have chitin in their cell walls.
* Either sexual or asexual reproduction or both may occur by spores. Spores or gametes can be motile or not. However, in the strict sense as fungi are currently defined, only those organisms that produce nonmotile spores and gametes are classifies as fungi. Nevertheless, we will be going over organisms that have motile spores, called Zospores and motile gametes.
Spores of Fungi:
a. Yeast:
Yeast are single-celled microorganisms that are classified, along with molds and mushrooms, as members of the Kingdom Fungi. Yeasts are evolutionally diverse and are therefore classified into two separate phyla, Ascomycota or sac fungi and Basidiomycota or higher fungi, that together form the subkingdom Dikarya. Budding yeast, also referred to as "true yeasts", are members of the phylum Ascomycota and the order Saccharomycetales. Such classifications are based on characteristics of the cell, ascospore, and colony, as well as cellular physiology.
b. Penicillium:
The name Penicillium comes from penicillus = brush, and this is based on the brush-like appearance of the fruiting structures under the microscope. Penicillium typically produces these brush-like heads. The stalk is called the conidiophore. The conidiophore branches at the tip. At the end of each branchlet is a cluster of spore-producing cells called phialides. A chain of spores is formed from the tip of each phialide. The spore is called a conidium 0r phialsopore. The spores in Penicillium often contain blue or green pigments which give the colonies on foods and feeds their characteristic colour. It is the spores in the blue cheese that give the colour to the cheese. The spores are only a few microns in diameter.
c. Mushroom:
A mushroom is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source.
d. Arbuscular Micchorhizae:
An arbuscular mycorrhizal fungus is a type of mycorrhiza in which the fungus penetrates the cortical cells of the roots of a vascular plant. Arbuscular mycorrhizas are characterized by the formation of unique structures, arbuscules and vesicles by fungi of the phylum Glomeromycota. AM fungi help plants to capture nutrients such as phosphorus, sulfur, nitrogen and micronutrients from the soil. It is believed that the development of the arbuscular mycorrhizal symbiosis played a crucial role in the initial colonisation of land by plants and in the evolution of the vascular plants.
ii. Bryophytes:
Bryophytes can be found in all ecosystems of earth. The diversity of bryophytes increases at tropical and subtropical latitudes. British Columbia has the highest bryophyte diversity in Canada so this is a wonderful place to study them. Another term commonly used for this group is nonvascular plants.
Bryophytes lack xylem and phloem, the conductive tissues of vascular plants. Bryophytes and tracheophytes are monophyletic and collectively called embryophytes. As the name implies, there is an embryonic stage in these organisms as contrasted with their closest relative of green algae.
All embryophytes have a life cycle that involves an alternation between sporophyte and gametophyte generations. In vascular plants it is the sporophyte is the dominant, obvious stage; the grasses, flowering trees, ferns, and conifers we admire are all sporophytes. They are the generation of the plant that produces the spores that will develop into the inconspicuous gametophyte stage. The gametophytes are tucked away and out of sight.
Bryophytes, on the other hand, have a conspicuous gametophyte stage (in most cases) that forms the green mats and tufts we see.
Unlike tracheophytes, it is the gametophyte stage that is composed of either stem and leaves or flattened ribbon-like thallus. The leaves of bryophytes are structurally very different from those of tracheophytes; they are generally one cell layer thick! The sporophyte of bryophytes is dependent on the gametophyte for water and nutrients and in most cases conspicuous.
Bryophytes, while very simple, exhibit a great diversity in growth form and habitat. There are bryophytes that can withstand extended periods of desiccation and others that are aquatic. You will find them on virtually every substrate: rocks, soil, tree bark, decaying wood, and even cars and other synthetic materials. Due to their diminutive stature and few human applications they have remained a largely overlooked group of organisms. Mosses, liverworts, and hornworts are the most ancient lineages of plants and can offer some clues about early plant evolution. While to most they seem small versions of their vascular relatives their life strategies have set them on a very different course. Many of their qualities are a reflection of this.
iii. Pteridophyte:
Pteridophytes in the broad interpretation of the term are vascular plants that reproduce and disperse via spores. Because they produce neither flowers nor seeds, they are referred to as cryptogams. The group includes ferns, horsetails, clubmosses, spikemosses and quillworts.
These do not form a monophyletic group, because ferns and horsetails are more closely related to seed plants than to lycophyte. Therefore, pteridophytes are no longer considered to form a valid taxon, but the term is still used as an informal way to refer to ferns and lycophytes, and some recent authors have used the term to refer strictly to the monilophytes.
Characteristics of Pteridophyte:
Occurrence:
* Most pteridophytes are terrestrial and grow in moist and shady places while some flourish well in open, dry places especially in xeric conditions. Some pteridophytes are aquatic and some are epiphytes.
* The sporophyte is the conspicuous and familiar plant body. It develops from the zygote, a diploid cell which results from the fertilization of the egg and antherozoid.
* The sporophytic plant body remains differentiated into true roots, stem and leaves. Some primitive members lack true roots and well developed leaves.
* The branching of the stem may be of monopodial or dichotomous type.
* There are two main categories of form and structure, one category comprises of megaphyllous types, in which the leaves are large in relation to the stem (e.g., ferns); the second comprises of microphyllous types in which the leaves are quite small in relation to the stem.
* All the vegetative parts of the sporophyte possess vascular supply.
Reproduction:
* The sporophytes reproduce by spores which are produced within sporangia.
* In some pteridophytes the sporangia develop on stems (i.e., cauline in origin) while in other they are borne either on the leaves (foliar) or in the axils of the leaves. The leaves that bear sporangia are known as sporophylls.
* The sporophylls may be widely scattered on a plant (e.g., ferns) or may be clustered in definite areas and structures called cones or strobili.
* In certain pteridophytes the sporangia are produced within specialized structure, the sporocarps.
* The sporangium in all pteridophytes is initiated by the laying down of a cross-wall in a superficial cell or a group of cells. Since this wall is periclinal each initial cell is divided into an outer and inner daughter cell. If the sporogenous tissue is derived from the inner daughter cell, the sporangium is described as "eusporangiate" (e.g., in most of pteridophytes) and if from the outer as "leptosporangiate" (e.g., in advanced pteridophytes).
* The sporophyte plant may be homosporous (e.g., Lycopodium, Dryopteris) or heterosporous (e.g., Selaginella, Isoetes, Marsilea).
The gametophyte:
* The spores on germination give rise to the haploid gametophytes or prothalli which are small and inconspicuous. The gametophytes in some pteridophytes are subterranean and in others they are retained within the resistant wall of the spore.
* The gametophyte or prothallus bears the sex organs, antheridia and archegonia. Normally, the gametophytes formed from the homospores are monoecious, that is both antheridia and archegonia are borne on the same gametophyte or prothallus. The gametophytes formed from the heterospores are dioecious, e.g., the antheridia and archegonia develop in separate male and female gametophytes.
The antheridia:
* The antheridia may be embedded in the gametophyte or they may project from it. The embedded antheridia are commonly found in eusporangiate pteridophytes while the projecting ones are usually found in the leptosporangiate ferns.
The Archegonia:
* The archegonia are flask-shaped. Each archegonium consists of a basal swollen, embedded portion the venter and a short neck. The venter encloses the egg and ventral canal cell.
Fertilization:
* In all cases the fertilization is accomplished by the agency of water. With the result of the fusion of male gamete and female egg a diploid zygote (2n) is formed.
The embryo:
* The zygote undergoes repeated divisions to form a new sporophyte. The young sporophyte remains attached to the gametophyte by means of a foot and draws nourishment from the prothallus until it develops its own stem, roots and leaves. The sporophyte is dependent on the gametophyte only during its early stages.
