eyespot
1. In certain unicellular algae, an organelle consisting of closely packed lipid globules (usually or always containing orange or red carotenoids); it is generally believed to be involved in phototaxis.

2. A disease of cereals caused by the fungus Pseudocercosporella herpotrichoides. Initially a dark smudge appears on the outer leaf-sheath, then an oval ‘eye-shaped’ lesion develops near the base of the plant, weakening the stem and leading to increasing susceptibility to lodging (i.e. being laid flat by weather). A similar disease, called sharp eyespot, is caused by Rhizoctonia solari.

eyespot (stigma)
1. A structure found in some free-swimming unicellular algae and in plant reproductive cells that contains orange or red pigments (carotenoids) and is sensitive to light. It enables the cell to move in relation to a light source (see phototaxis).

2. A spot of pigment found in some lower animals, e.g. jellyfish.

3. An eyelike marking on the wings of certain insects, which is revealed in startle displays.