TRENDS IN SYSTEMATIC BOTANY
81
sharply as are the taxonomic categories, which are based largely on
morphology. The former categories, however, have an objectivity that
can be measured more precisely than that of the usual taxonomic categories, which are accordingly more subjective. A difficulty arises in
obtaining enough experimental data about a group of plants to fix it
precisely in the Turesson classification.
The Ecotype.
This group, the equivalent of ecological race, is composed of all those individuals or local populations of the species that
are fitted to survive in a particular set of environmental conditions.
These conditions, each of which represents one of the major environments occupied by the species as a whole, may be climatic or sometimes
edaphic, and the fitness of the individuals to them is primarily physiologic. A species that is a restricted endemic may be composed of only
one ecotype; a widespread species, on the other hand, may consist of
several ecotypes, each of which competes best in the set of conditions to
which it is adapted. Accordingly, ecotypes (which have no barriers to
interbreeding) are kept apart by natural selection.
The California transplant experiments, in which samplings from various parts of the range of each of many widespread species were
brought together in a uniform garden, and vegetative propagules of
these were grown in other uniform gardens in quite different climates,
disclosed that ecotypes are in various stages of evolution, from incipient
to mature, as might be anticipated.
An interesting analysis of incipient ecotypes in Galium pumilum is
given by Ehrendorfer (1953b). In a large population of this species in
the Vienna Woods, containing both pubescent and glabrous individuals,
the average of pubescent plants was increased by over 15% in dry sunny
places as contrasted with moist shady spots.
Kruckeberg (1951) found that one of the climatic ecotypes of Achillea
borealis ssp. californica from the western base of California's Sierra
Nevada contained both serpentine-tolerant and serpentine-intolerant
edaphic races. This led him to point out that since the environment of
any particular place is a complex, no single uniform ecotypic response is
possible, and that it might be better to think of natural populations as
consisting of continuous or discontinuous arrays of ecotypic variation in
response to the sum total of the environmental factors in an area. The
same idea has been brought up many times.
At times, the ecotype may be the equivalent of the subspecies or geographic variety, depending upon the amount of morphological distinctness that it possesses; at other times, a subspecies may consist of several
morphologically very similar but physiologically distinct ecotypes. Eco-
81
sharply as are the taxonomic categories, which are based largely on
morphology. The former categories, however, have an objectivity that
can be measured more precisely than that of the usual taxonomic categories, which are accordingly more subjective. A difficulty arises in
obtaining enough experimental data about a group of plants to fix it
precisely in the Turesson classification.
The Ecotype.
This group, the equivalent of ecological race, is composed of all those individuals or local populations of the species that
are fitted to survive in a particular set of environmental conditions.
These conditions, each of which represents one of the major environments occupied by the species as a whole, may be climatic or sometimes
edaphic, and the fitness of the individuals to them is primarily physiologic. A species that is a restricted endemic may be composed of only
one ecotype; a widespread species, on the other hand, may consist of
several ecotypes, each of which competes best in the set of conditions to
which it is adapted. Accordingly, ecotypes (which have no barriers to
interbreeding) are kept apart by natural selection.
The California transplant experiments, in which samplings from various parts of the range of each of many widespread species were
brought together in a uniform garden, and vegetative propagules of
these were grown in other uniform gardens in quite different climates,
disclosed that ecotypes are in various stages of evolution, from incipient
to mature, as might be anticipated.
An interesting analysis of incipient ecotypes in Galium pumilum is
given by Ehrendorfer (1953b). In a large population of this species in
the Vienna Woods, containing both pubescent and glabrous individuals,
the average of pubescent plants was increased by over 15% in dry sunny
places as contrasted with moist shady spots.
Kruckeberg (1951) found that one of the climatic ecotypes of Achillea
borealis ssp. californica from the western base of California's Sierra
Nevada contained both serpentine-tolerant and serpentine-intolerant
edaphic races. This led him to point out that since the environment of
any particular place is a complex, no single uniform ecotypic response is
possible, and that it might be better to think of natural populations as
consisting of continuous or discontinuous arrays of ecotypic variation in
response to the sum total of the environmental factors in an area. The
same idea has been brought up many times.
At times, the ecotype may be the equivalent of the subspecies or geographic variety, depending upon the amount of morphological distinctness that it possesses; at other times, a subspecies may consist of several
morphologically very similar but physiologically distinct ecotypes. Eco-