178
J. HESLOP-HARRISON
pulchella. In this situation the habitats, although adjoining, were distinct. In others studied, particularly in the East Anglian fens where
human intervention has blurred ecological boundaries, many nondescript, intermediate habitats exist. I n these the D. incarnata populations
are heterogeneous, and the character combinations typifying the named
subspecies are often broken up. The probable role of floral characters
in contributing to the reproductive isolation of the ecological races of D.
incarnata (Heslop-Harrison, 1958) is mentioned in alater section (p, 212).
The pattern of ecological differentiation in D. incarnata is one of
distinct yet intermingled races; in other species of the genus a bolder
regional differentiation is evident, reminiscent of that described by the
Carnegie group in Potentilla glandulosa. The aggregate D. maculata
consists of two ecospecies, D. fuchsii and D. maculata, the former diploid
and the latter tetraploid, which show different ecological tolerances
throughout the European range (Heslop-Harrison, 1951). Each of these
in turn contains regional subspecies of an ecotypic nature. D. fuchsii,
for example, is represented in the British Isles by three forms, distinct
enough to have been acknowledged taxonomically as subspecies, fuehsii,
hebridensis and okellyi. Subsp. fuchii is wide-ranging, occurring in
meadows and open woodland on neutral or moderately basic soils;
subsp. hebridensis replaces subsp. fuchsii along the western seaboard in
regions of extreme oceanic climate from Cornwall, through western
Ireland and the Hebrides to Sutherland, while subsp. okellyi is restricted
to areas of karst-like limestone in Ireland and north-western Scotland
(Heslop-Harrison, 1953aJ 1958). The subspecies are distinguished by
several correlated morphological features, maintained in cultivation,
and also to some extent by phenology. They have the aspect of distinct
races which have attained their present distributions independently, but
again this can be no more than a subjective judgment.
I n some recorded examples of genecological differentiation, the evidence is inadequate to attempt any kind of distinction between possible
monotopic or polytopic origins, Thus Habeck (1958) has studied the
variation in seedlings from seed samples of Thuya occidentalis from
twenty-nine sites within the distributional area in Wisconsin. The
sampling sites were classified into “typical lowland swamps” and “well
drained uplands”. Marked differences in response t o three conditions of
soil moisture were observed in cultivation, and Habeck concluded that
two distinct ecotypes, one adapted to the upland conditions and the
other to the lowland, co-exist in Wisconsin throughout the species area.
Nothing in the recorded data serves to establish whether two races
different in origin are involved, or whether the ecotypes have evolved
polytopically in response to local selective pressures.
The same kind of difficulty arises in interpreting ecological races oon-
J. HESLOP-HARRISON
pulchella. In this situation the habitats, although adjoining, were distinct. In others studied, particularly in the East Anglian fens where
human intervention has blurred ecological boundaries, many nondescript, intermediate habitats exist. I n these the D. incarnata populations
are heterogeneous, and the character combinations typifying the named
subspecies are often broken up. The probable role of floral characters
in contributing to the reproductive isolation of the ecological races of D.
incarnata (Heslop-Harrison, 1958) is mentioned in alater section (p, 212).
The pattern of ecological differentiation in D. incarnata is one of
distinct yet intermingled races; in other species of the genus a bolder
regional differentiation is evident, reminiscent of that described by the
Carnegie group in Potentilla glandulosa. The aggregate D. maculata
consists of two ecospecies, D. fuchsii and D. maculata, the former diploid
and the latter tetraploid, which show different ecological tolerances
throughout the European range (Heslop-Harrison, 1951). Each of these
in turn contains regional subspecies of an ecotypic nature. D. fuchsii,
for example, is represented in the British Isles by three forms, distinct
enough to have been acknowledged taxonomically as subspecies, fuehsii,
hebridensis and okellyi. Subsp. fuchii is wide-ranging, occurring in
meadows and open woodland on neutral or moderately basic soils;
subsp. hebridensis replaces subsp. fuchsii along the western seaboard in
regions of extreme oceanic climate from Cornwall, through western
Ireland and the Hebrides to Sutherland, while subsp. okellyi is restricted
to areas of karst-like limestone in Ireland and north-western Scotland
(Heslop-Harrison, 1953aJ 1958). The subspecies are distinguished by
several correlated morphological features, maintained in cultivation,
and also to some extent by phenology. They have the aspect of distinct
races which have attained their present distributions independently, but
again this can be no more than a subjective judgment.
I n some recorded examples of genecological differentiation, the evidence is inadequate to attempt any kind of distinction between possible
monotopic or polytopic origins, Thus Habeck (1958) has studied the
variation in seedlings from seed samples of Thuya occidentalis from
twenty-nine sites within the distributional area in Wisconsin. The
sampling sites were classified into “typical lowland swamps” and “well
drained uplands”. Marked differences in response t o three conditions of
soil moisture were observed in cultivation, and Habeck concluded that
two distinct ecotypes, one adapted to the upland conditions and the
other to the lowland, co-exist in Wisconsin throughout the species area.
Nothing in the recorded data serves to establish whether two races
different in origin are involved, or whether the ecotypes have evolved
polytopically in response to local selective pressures.
The same kind of difficulty arises in interpreting ecological races oon-