Some cytotaxonomic problems in the fern genera Asplenium and Polystichum

The basic aim of this research project is to attempt to
obtain information concerning the phyletic affinities between
species by means of a study of chromosome pairing in synthesised
hybrids. Any evidence obtained is supplemented by a consideration
of the morphology, ecology and geographical distribution of the
species concerned.
The main problem consisted of a cytogenetic investigation
into the relationships of the four European Polystichum species,
although this soon resolved into the two immediately accessible
problems of the affinities and possible origin of the two tetraploids
P. braunii (continuing the observations of Manton &
Reichstein, 1961) and P. aeuleatum. Attempts were made to resynthesise
the latter species from it s postulated parents
(Manton, 1950).
Polystichum is a slow-growing fern and it was known that
synthesised hybrids may need up to three years to produce
sporangia. Because of the possibility that hybrids obtained
might mature too slowly to yield results in the time available
an additional investigation involving some Asplenium species was
begun. In this genus many hybrids produce sporangia within a
year of fertilisation, thus permitting a rapid extension of the
hybridisation programme. This considerable advantage has converted
a secondary investigation into the mutual affinities: of
two European tetraploids (A. forisiense and A. macedonicum) into a
major project, and the hybridisation programme was expanded to
include a number of other European species at both diploid and
tetraploid levels. Much new material was made available from the
personal collections of Professor Eeichstein of Basel, who was
also responsible for obtaining an important collection of living
Polystichum species from Japan by arrangement with Professor H. Ito
of Tokyo. Both investigations have therefore extended beyond the
bounds first envisaged but since the work on Asplenium is more
nearly complete it will be convenient to deal with it first in the
account which follows.
Each genus is treated separately as a distinct section with
the exception of the account of the methods used, which follows, and
the General Discussion, which will be found at the end of the thesis.