Euphorbia Flanaganii F. Cristata is a crested form of the Euphorbia Flanaganii. As the plant matures you can expect it to reach around 15 cm (6″) tall and about 30 cm (12″) in diameter. When looking at an image of the plant you will notice the strong bright green colour that is one of the plants most dominant feature along with the Cristata fan like top of the plant. Most people find the plant to resemble a green coral.
Source: Succulents Network