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Laminaria sp. (kelp), a brown algae
Laminaria sp. (kelp), a brown algae
The seaweed called kelp (Laminaria sp.) is a widespread brown algae with roots called holdfasts, a main stem or stipes, and long fronds called blades. It belongs to the kingdom Chromalveolata, the phylum Heterokontophyta, class Phaeophyceae, the order Laminariales, and the family Laminariae. A common seaweed today, kelp first appeared in the Miocene period between 15 and 5 mya.
Kelp grows in extensive forests in shallow ocean floors and coastlines around the world. It requires nutrient-rich water with temperatures between 6 and 14 C (43 and 57 F). The diameter of kelp's fronds or blades is 30-80 m. They are known for their high growth rate. The growth occurs at the base of the meristem, when the stipes (stems) and blades meet.
While kelp has various parts that in some ways resemble those of land plants, their thallus tissue lacks the specialized, distinctive vascular structures of roots, branches, or leaves found in land plants. The rootlike tendrils called holdfasts, the central stem or stipes, and the leaf-like blades of kelp are all composed of similar thallus cells which are homogenous in structure. In spite of its having these various structures, all cells from all parts have chloroplasts and perform photosynthesis.
The
thallus tissue of algae may be contrasted to the more specialized
vascular tissues of land plants, where only the leaf cells have
chloroplasts. Root cells of land plants are specialized to absorb
water, and their stem or trunk cells are designed for both structural
strength and the transmision of liquids.
Vascular plant structures did not begin to develop until the Silurian and Devonian periods (440-360 mya), about 40-50 million years after green algae of the Chlorophyta division started to colonize shorelines and estuaries, and evolved into land plants. .
Reference
Taylor, E.L., T.N. Taylor, and M. Krings 2009. Paleobotany: The Biology and Evolution of Fossil Plants. New York, Academic Press.
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