The shape of seeds
Fluffy seeds have lots of hairs surrounding them. These hairs are of little assistance in distribution but do play other important roles. The hairs are hydroscopic and as the humidity rises they absorb moisture twisting as they do so to firmly lock the seeds onto the soil surface. There also seems to be a natural glue released, for they also stick very firmly onto smooth surfaces. When it rains the hairs absorb a large quantity of water that helps to keep the keep the seed moist while it germinates.
Fluffy seeds include Rhodanthe chlorocephala Dry(L) and Wet(R)
Seeds with tails are more easily carried by the wind thus helping distribution. Some seeds are very light and may be carried a considerable distance. On the surface the tail assists with movement to a low, and hopefully damp spot. Eventually the tail will break off leaving the seed in its new location.
Seeds with tails include Bellida graminae and Podolepis kendallii
Very fine seeds often, but not always, have tails. Some are dispersed by being thrown from the flower head on a windy day, others are carried by surface water and yet others are retained in the old flower head which then becomes the vehicle for distribution.
Very fine seeds include Waitzia nitida and Podolepis rugata
Cephalipterum drummondii is different in that it produces capsules instead of individual seeds. Each capsules consists of a few seeds inside a mass of fine hair. Capsules are ejected when mature but only a few centimetres from the plant where they may blow around a little further. The hairs are hygroscopic so also act to lock the capsule onto the soil surface as well as holding moisture around the germinating seeds. We try to handle these seeds as little as possible because of their tendency to knit together into one big lump that then has to be pulled apart with tweezers.
A few plants produce seeds that are smooth and disc shaped. Trachymene coerulea is one and so too do members of the Hyalosperma genus. In some cases the seeds do have tails when in the flower but break off before distribution. The seeds are normally flicked out a short distance by wind gusts.
We can find no reference to seeds being dispersed by animals but speculate that the seeds of Podotheca gnaphaloides might be because we know all too well that the tips are sharp enough to stick into human skin and the long tails have very fine barbs on them that makes them feel sticky.