European Red List of Vascular Plants - European Commission

fertilisation. As a consequence many plant populations are
clonal, such that the same genetic individual may extend
over kilometres or even throughout entire river systems.
This likelihood has been supported by the fact that all
plants of some alien taxa such as nuttall’s and Canadian
waterweed (Elodea nuttallii and E. canadensis) in the UK
are female and most derive from a very small number of
introductions, but they have been capable of spreading
more or less throughout the region. The capacity of plants
to spread by creeping stems and stolons, combined with
their capacity to spread by vegetative methods, means
that it is difficult or impossible to delineate a single plant.
Without this capacity it is almost impossible to assess the
size of a population, let alone measure trends.
This lack of genetic variation also means that it is difficult
to interpret abundance in terms of the potential survival
of the species. For example, in the UK it appears likely
that the population of floating water-plantain (Luronium
natans) in the Montgomery Canal, which numbers
millions of plants, is genetically identical or at least shows
very low genetic diversity, in contrast, populations in
natural water bodies in the Welsh mountains appear to
be very genetically diverse (Kay et al. 1999), but they
are much smaller. Without genetic data, it might be
concluded that the species is not of conservation concern
because of the presence of vast populations, however in
genetic terms, the high altitude populations are small
and highly vulnerable and represent most of the genetic
diversity of the species in the UK.
the conservation status of populations have in many cases
been made simply based on the number of sites from
which a taxon is recorded. There are many aquatic plant
taxa in Europe which are known to be declining in some
areas, but appear to be frequent in other areas. Without
numerical data it has been impossible to interpret this
in relation to the IUCN classes and these species are
generally listed as Least Concern.
The information collected at species level shows that
about 16% of the European aquatic plants are considered
to be declining whereas around two thirds (64.3%) of
them seem to have stable populations. A small fraction
(1.3%) has an increasing population trend and the trend
of about one fifth (18.6%) is unknown (Figure 25).
Figure 25. Population trends of European aquatic plants
For most aquatic plant taxa we lack both the numerical
data that would enable trend analysis and genetic
information that would enable assessment of the relative
importance of different populations and so decisions on
Nymphaea candida is widespread in Europe with stable populations and is currently assessed as Least Concern. Photograph © Richard V. Lansdown.
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