176
J. HESLOP-HARRISON
species do meet, their ecological limitations severely inhibit natural
hybridization.
Not all of the ecologically-correlated variation within the section
Cerastes is accounted for by this sub-division. While some of the
narrowly ranging species seem reasonably uniform, Ceanothw gloriosus
shows further differentiation into maritime and inland races, also given
taxonomic recognition, as varieties. C. cuneatw has “developed numerous recognizable forms”, and “the aggregations of characters that typify
each form follow essentially a clinal transition which coincides with a
gradual ecological gradient . . .,’.
The common feature of the three examples from the Californian flora
outlined in the preceding paragraphs is that vicarious ecological races
are seemingly present, distinct from each other in morphological and
physiological characteristics. The ecological races are all evidently themselves heterogeneous to a greater or lesser degree, showing local variation which is probably both adaptive and non-adaptive. The fact that
the situations in the three genera have been given different taxonomic
treatment is confusing but irrelevant; it merely indicates that in polytypic species complexes the taste of the individual worker tends to be
the arbiter so far as nomenclature is concerned.
2. Ecological Races with Interdigitating or Mosaic Distribution-s
There are now several well-documented examples of ecologically
differentiated races which do not possess vicarious areas but overlap
geographically, each occupying its own characteristic type of habitat
within the common area. Again, varying taxonomic treatments tend to
obscure the essential similarity of many cases. By the criterion of free
gene exchange in experimental crosses sympatric ecological races may
merit inclusion in one and the same ecospecies, but their nomenclatural
treatment normally depends upon their degree of morphological
differentiation. If this is conspicuous and consistent they will, quite
justifiably, be generally named as species; otherwise they may be classified as subspecies, or may even escape taxonomic recognition altogether.
The example of the Ranunculus lappaceus group in south-eastern
Australia is one of the most remarkable yet described (Briggs, 1962).
Seven named species occur in the 5 000-6 000-ft altitude zone of the
Kosciusko plateau. All are closely similar in karyotype, and are recorded
as being freely interfertile ; they may thus be regarded as being part of
the same ecospecies. The different races show very narrow ranges of
ecological tolerance, and, since the characteristic habitats are scattered
throughout the area, they have a mosaic distribution.
The faithfulness of the races to their particular habitat is evidently
extremely strong. The situation is illustrated by R. millanii and R. dis-
J. HESLOP-HARRISON
species do meet, their ecological limitations severely inhibit natural
hybridization.
Not all of the ecologically-correlated variation within the section
Cerastes is accounted for by this sub-division. While some of the
narrowly ranging species seem reasonably uniform, Ceanothw gloriosus
shows further differentiation into maritime and inland races, also given
taxonomic recognition, as varieties. C. cuneatw has “developed numerous recognizable forms”, and “the aggregations of characters that typify
each form follow essentially a clinal transition which coincides with a
gradual ecological gradient . . .,’.
The common feature of the three examples from the Californian flora
outlined in the preceding paragraphs is that vicarious ecological races
are seemingly present, distinct from each other in morphological and
physiological characteristics. The ecological races are all evidently themselves heterogeneous to a greater or lesser degree, showing local variation which is probably both adaptive and non-adaptive. The fact that
the situations in the three genera have been given different taxonomic
treatment is confusing but irrelevant; it merely indicates that in polytypic species complexes the taste of the individual worker tends to be
the arbiter so far as nomenclature is concerned.
2. Ecological Races with Interdigitating or Mosaic Distribution-s
There are now several well-documented examples of ecologically
differentiated races which do not possess vicarious areas but overlap
geographically, each occupying its own characteristic type of habitat
within the common area. Again, varying taxonomic treatments tend to
obscure the essential similarity of many cases. By the criterion of free
gene exchange in experimental crosses sympatric ecological races may
merit inclusion in one and the same ecospecies, but their nomenclatural
treatment normally depends upon their degree of morphological
differentiation. If this is conspicuous and consistent they will, quite
justifiably, be generally named as species; otherwise they may be classified as subspecies, or may even escape taxonomic recognition altogether.
The example of the Ranunculus lappaceus group in south-eastern
Australia is one of the most remarkable yet described (Briggs, 1962).
Seven named species occur in the 5 000-6 000-ft altitude zone of the
Kosciusko plateau. All are closely similar in karyotype, and are recorded
as being freely interfertile ; they may thus be regarded as being part of
the same ecospecies. The different races show very narrow ranges of
ecological tolerance, and, since the characteristic habitats are scattered
throughout the area, they have a mosaic distribution.
The faithfulness of the races to their particular habitat is evidently
extremely strong. The situation is illustrated by R. millanii and R. dis-