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PHYCOLOGICAL SOCIETY OF AMERICA

Delesseria decipiens Morphology

Thallus Delesseria decipiens generally grows in clusters of blades, with the main axis of the thallus ranging anywhere form 4 cm to more than 50 cm. The cells that make up the thallus of D. decipiens are relatively undifferentiated, although the alga maintains distinct structural features. Most prominent in the appearance of D. decipiens is the presence of a polystromatic midrib (more than one cell layer thick), centered between two monostromatic blades or wings. Further branching off of the midrib gives the algae its beautiful wing like appearance as it produces lateral branches off the midrib. The blades of D. decipiens are rather delicate and are often worn away from the older parts of the seaweed as the plant continues to grow and branch so that all that remains of many of the older branches is the thick midrib.   D. decipiens can range from bright red to dark maroon or purple in color. The width and the degree of roundedness of the tips of the blades also seem to vary considerably by individual. Top

Cell structure of monostromatic blade (below left), magnification 400 times

Pseudoparenchymatous Construction While the blades of D. decipiens might resemble the generalized parenchymatus growth responsible for the thin cell walls and sheet like structure of the green algae Ulva, its construction and growth is in fact very different, resulting in the classification of its growth as pseudoparenchymatous construction. While Ulva’s growth can occur in many directions in the thallus of the algae, Delesseria’s regions of growth and division are much more specific. Delesseria’s structure is in fact an aggregate of filaments, with each midrib containing a chain of central axial cells, each surrounded by four pericentral cells. These pericentral cells divide from the axial cell in a particular fashion, with the first two dividing in the plane of the flat blade and the second two dividing from the axial cell perpendicular to the plane of the blade. These pericentral cells will divide to form veins extending away from the midrib resulting in the delicate monostromatic wing. The division of the pericentral cells into lateral veins is a highly organized process, taking place by the intercalary division (divisions not at the apical cell) of the pericentral cell and associated cells in the blade of the weed. The midrib continues to grow and thicken, serving as a storage place for starch, but the cells of the main axis do not continue to divide, an important characteristic of the genus Delesseria. Like many members of the Division Rhodophyta, D. decipiens also has pit connections between its cells, forming connections between the cytoplasm of adjacent cells. Top

Apical Growth In a blade of Delesseria decipiens, there are two main areas of growth. As previously discussed, pericentral cells of the midrib divide by way of intercalary divisions to form the thin lateral veins that make up the delicate wing of the D. decipiens. Localized growth occurs at the tips of each blade where a broad apical cell divides uniaxially (with one axis), initially forming cells that look much wider than they are tall. These axial cells will divide further to form four pericentral cells. The axial cells can then grow and elongate, but do not undergo any other divisions. Top

Apex of third order branch showing apical cell growth,
magnification 400 times

Schematic of apical cell growth
Drawing from Fritsch, 1945 

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