Origins, boundaries and disruptions
In theory, the geographical location of a taxon’s centre of origin should have a fundamental effect on the nature and orientation of a distribution pattern. Granted that many, though by no means all, taxa have only a limited dispersal capacity, the developing distribution is likely to cluster around the centre of origin for a long period of time after the moment of origin. The evolutionary sequence drawn up by Holland for the genus Aloe accepts that the herbaceous forms are less advanced than the arborescent. Of the internal factors governing plant distribution, the most important factor controlling the final character of the boundary of that distribution is, without doubt, the autecology of the plant in question. Granted that the plant has the time and the dispersal ability to occupy all available habitats, it will be the distribution and shape of these habitats which will determine the pattern of the plant’s geographical range.