DIASPORE SHAPE is a dimensionless index ranging from 0 to ca. 0.23. It describes the deviation of a diaspore's shape from a sphere in three dimensions. 0 addresses a perfect sphere, whereas values > 0 addresses flat or elongated diaspores.
The dimensionless index DIASPORE SHAPE (column code: DIA_SHAPE) is calculated as the variance of the standardized mean size of the three dimensions of the diaspore (Fig. 1; additionally see Diaspore Size) (Thompson et al., 1993).
Fig. 1. Calculation of DIASPORE SHAPE for dandelion (Taraxacum Sect. Ruderalia).
DIASPORE SHAPE is calculated from all information on diaspore size that was available. Accordingly, it cannot be directly calculated from the presented information on diaspore size in some species.
Bekker, R.M., Bakker, J.P., Grandin, U., Kalamees, R., Milberg, P., Poschlod, P., Thompson, K. & Willems, J.H. (1998): Seed size, shape and vertical distribution in the soil: indicators of seed longevity. Functional Ecology 12, 834-842.
Thompson, K., Band, S.R. & Hodgson, J.G. (1993): Seed size and shape predict persistence in soil. Functional Ecology 7, 236-241.