<div class="views-field views-field-field-product-summary tb"> <div class="field-content"> <p>The umbrella alga grows singly or in clusters. Each individual thallus consists of a single cell with a single nucleus. There is a holdfast where the alga is attached to the substrate and a long, slender, calcified stipe or stalk. The thallus is emerald green and cup-shaped, or occasionally flattened, with twenty two to thirty rays. The stipe is up to 7 centimetres (2.8 in) long and the disc up to 7 millimetres (0.28 in) in diameter. In immature specimens, the stipe has a complex structure of short branches but by the time the alga reaches maturity, only the scars of these remain.</p> </div> </div> <p> </p>