Marine Botany

Morphology

Juvenile

The following are selections from herbarium sheets from the Gilbert M. Smith Herbarium.  After fertilization of the female egg by the male sperm, the sporophyte begins to develop on top of the female gametophyte.  The fertilized egg enlarges, and then divides.

small juvenile kelp

The lower half grows downward to form a small, delicate holdfast.  The upper half then divides and grows upwards, and forms a small blade.  Between the holdfast and blade, a thin cylinder takes shape, the stipe.  Within a few weeks, the juvenile sporophyte will overgrow the female gametophyte at its base.

two young blades

In some cases, multiple blades may arise from the small holdfast early on.  But this is not always the case.

juvenile kelp

A small split emerges at the junction between stipe and blade.  Before the first tear is complete, new splits occur, making two blades into four, then eight and so forth.  At the intersection between blades and stipe, pneumatocysts form that raise the blades.  The stipes enlarge and send the fronds upwards towards the surface (Connor and Baxter 1989).  A scimitar blade caps every frond producing new blades on the frond.

herbarium sheet

Above is a picture of an older juvenile.  Notice the tears at the blade and stipe intersections.  Only a few pneumatocysts have formed on this specimen in its development.

Copyright 2001:  James Lopez

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