CYTOTAXONOMIC STUDIES IN THE SECTION ANNUl OF SENECIO
Abstract
Seneclo scualidus, a Mediterranean endemic, became
established in Britain about 180 years ago, where it is
now common and widespread.
S. saualidus is represented in Sicily by two distinct
taxa: the lowland S. chrysanthemif'olius, and the montane
S aetnensis. On the basis of their distinctiveness these
taxa are retained as separate species. Where these two
species meet they form hybrid swarms, and bipolar
introgression occurs. The British S.s pualidiis is
morphologically intermediate between the two Sicilian species,
but its autonomy and circumscribed morphology indicate that
it should be treated as a distinct species of hybrid origin.
In Britain, , squalidus (2n = 20) hybridises with
S. vular1s and S. viscosus (both 2n = 1+0). Both triploid
hybrids are very highly sterile.
A ligulate variety of S. vulgaris shows a close
geographical and historical correlation with the spread of
S. scualidus in Britain, and indicates introgresslon into
S. vulgaris from S. squalidus. The rare occurrence of
segregating fertile hybrid material supports this hypothesis.
- Experiments snow that introgresslon can occur via the
rare seed set by the triploid F1 S. saualldus X S, viscosus
at the more or less pentaploid level (2n = 1+7 - 50).
Subsequent generations from these pentaplolds tend towards
the teraploid level and increasing fertility. This may be
analogous to the method of introgression Into S. vularis.
S. cambrensis, an allohexaploid (2n = 60) from
S vulgaris X S. squalidus, has arisen in Britain, probably
within the last 50 years, and is still restricted to north
Wales and Cheshire. This species Is now segregating into
ligulate and eligulate races.
Authors
Crisp, Peter ColinCollections
- Theses [4223]