Female gametangia are not enclosed by a wall of sterile cells as in higher cryptogams. Reproduction may be isogamous, anisogamous, or oogamous. We are still discovering new algae, sometimes whole groups of them at a time.Īlgae of other groups usually have two flagella (singular: flagellum). Spores may be motile or non-motile, and this varies from phylum to phylum, e.g., the red and blue-green algae are non-flagellated and are essentially non-motile.Īlgae of one kind or another have been around for over 2 billion years. They have no need for water-conducting tissues as they are, at leaset at some stage, surrounded by water. Internal transportation? Some of the larger kelps have translocation (transport of photosynthetic products) but most do not. So sex was not somthing invented yesterday. In all probability, an alga was the first organism to have something that we would recognise as sex, about 1.3 billion years ago (i.e. Sex? Algae also have sex, sometimes a very simple kind of sex where the algae themselves act as gametes, but also very complicated sex with egg and sperm-like cells. Some are colonial and motile in the adult phase like Volvox (right, photograph © Karl Bruun). Most algae form some sort of spore, which is a cell - often motile - that serves to reproduce the organism with combining with another cell. In general, we can say that they are simple organisms composed of one cell, or grouped together in colonies, or as organisms with many cells, sometimes collaborating together as simple tissues. In addition to the pigmentation, they differ considerably in many ultrastructural and biochemical features including photosynthetic pigments, storage compounds, composition of cell walls, presence/absence of flagella, ultrastructure of mitosis, connections between adjacent cells, and the fine structure of the chloroplasts. Distinguishing these three groups, however, involves more substantial differences than indicated by this simple designation. They belong to threeĭifferent groups, empirically distinguished since the mid-nineteenth century by the Irish botanist William Henry Harvey (1811-1866) on the basis of thallus color: red algae (phylum Rhodophyta), brown algae (phylum Ochrophyta, class Phaeophyceae), and green algae (phylum Chlorophyta, classes Bryopsidophyceae, Chlorophyceae, Dasycladophyceae, Prasinophyceae, and Ulvophyceae).
Marine macroalgae, or seaweeds, are plant-like organisms that generally liveĪttached to rock or other hard substrata in coastal areas. This genetic diversity is reflected in the enormous biodiversity exhibited by algae in terms of morphological, ultrastructural, ecological, biochemical, and physiological traits. Quite simply, what we call "algae" is an artificial and highly heterogeneous aggregation of organisms belonging to many different evolutionary lineages, and therefore highly diverse from a genetic point of view. As conceived in the broadest sense, algae are oxygen-generating, photosynthetic organisms other than embryophyte land plants, fungi and lichens. We use the term "algae" very loosely, simply because coralling them is so very difficult. Some algae (most the greens and the reds) are indeed related to the land plants, and some flagellated algae are related to the protists, but there is no justification for the including all algae in any generic term other than "algae". According to the most recent phylogenetic studies, both are not quite correct. Pronunciation: Algae ("al'jay" or "al'gay", both are used today) is the plural Alga ("al'ga") is the singular, but here is no such thing as "algaes".Īlgae are very simple chlorophyll-containing organisms: some say that they are plants other say that the are not, calling them protists or protoctists.
Euglenozoa), and the Kingdom Bacteria (Blue-green algae). phaeophytes - brown algae - dinoflagellates, and diatoms), the Kingdom Protozoa (e.g. chlorophytes and rhodophytes - green and red algae), the Kingdom Chromista (e.g. Molecular phylogeny (gene sequencing) and other characters show they belong to four kingdoms: Kingdom Plantae (e.g. The plant body is relatively undifferentiated, and there are no true roots and leaves.Īlgae are not a single taxonomic entity. Algae are pond scums, terrestrial algae, snow algae, seaweeds, freshwater and marine phytoplankton.
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