The mode of dispersal of the ‘dispersule’ (or propagule = unit of seed, fruit or spore as it is dispersed) has obvious consequences for the distances it can cover, the routes it can travel and its final destination.
How to classify?
This is a categorical trait. Record all categories that are assumed to give significant potential dispersal (see Box 4), in order of decreasing importance. In the case of similar potential contributions, prioritise the one with the presumed longer-distance dispersal; e.g. wind dispersal takes priority over ant dispersal.
It is important to realise that dispersules may (occasionally) get transported by one of the above modes even though they have no obvious adaptation for it. This is particularly true for endo-zoochory and exo-zoochory. Note that there is ample literature (e.g. in Floras) for dispersal mode of many plant taxa.
References on theory, significance and large datasets: Howe and Smallwood (1982); Van der Pijl (1982); Bakker et al. (1996); Howe and Westley (1997); Hulme (1998); Poschlod et al. (2000); McIntyre and Lavorel (2001); Tackenberg et al. (2003); Myers et al. (2004).
More on methods: Howe and Westley (1997); Forget and Wenny (2005); Pons and Pausas (2007).