To paraphrase the BSBI's national web site, axiophytes are "worthy plants" - the 40% or so of species that arouse interest from botanists as indicators of habitat that is considered important for conservation, such as ancient woodlands, clear water and species-rich meadows.
They are not the same as rare plants: species that have only ever been recorded in one or two sites in a county may have relatively low statistical significance when considering vegetation patterns as a whole. (Actually this is a debatable point, as their constancy in a particular habitat in the wider world may count for more than their frequency in an arbitrary geographical area.)
Lists of axiophytes are one technique for determining conservation priorities. Sites with many axiophytes are usually of greater importance than those with fewer; and changes in the number of axiophytes in a site over time can be used for monitoring the outcome of management practices.
The BSBI nationally has identified three criteria for defining an axiophyte.
In Hampshire we have considered these criteria and made some adjustments. We have retained the rarity criterion for the present, although we do not consider it particularly meaningful. Of more concern is the 90% restriction. There are several species which are indicators of good habitat but also make an appearance in other situations considered less conservation-worthy. To include these indicriminately in a list would result in an undesirable number of 'false positives', even at the 90% / 10% level. On the other hand, to exclude them would be to lose information of value in many situations.
As a result, we have defined two categories of axiophyte:
Strict axiophytes are therefore listed together with the habitats for which they can be considered valid. The habitat classification is based on the Broad Habitat Classification developed for the UK Biodiversity Action Plan (2000). Habitats relevant to Hampshire vascular plants are listed at the link below.