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Studies of variation in some Tasmanian species of Plantago L.


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Brown, MJ 1979 , 'Studies of variation in some Tasmanian species of Plantago L.', PhD thesis, University of Tasmania.

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An experimental investigation of the variation exhibited by
some Tasmanian species of Plantago has been conducted. The study
combines field~ glasshouse and herbarium investigations with
multivariate analytic techniques to examine adaptive strategies
within the genus.The major portion of the study concerns leaf-shape variation
in P. glabrata and P. paradoxa. The leaf-shape of these species
is divergent in summer but converges under winter conditions. The
degree of convergence is limited by habitat. Transplant
experiments show a marked convergence in the shapes of winterleaves
when plants are grown in the same environment. The
characters measured were the width, the position of the widest
part and the petiole length of the leaves relative to their total
length. The field analyses indicate that these characters vary
independently. When grown in the glasshouse, both species respond
to changes of temperature, light intensity, photoperiod and
inundation, factors which differentially affect the various leaf
characters. Progeny testing shows that only the relative leaf-width
is strongly heritable in P. glabrata, whereas in P. paradoxa the
position of the widest part of the leaf is also strongly and
independently heritable. The implications of the studies are
discussed in relation to the maintenance of adaptive variation in
the species with respect to season.
A second part of the study is concerned with intra- and interspecific
variation in some Plantago species. Variation in leaf-shape
is correlated with microhabitat in two populations of P. paradoxa.
Progeny testing demonstrates that differences of leaf shape between populations are masked by canalization within populations. In one
of the populations, the differences in leaf-shape are phenotypic
modifications, whilst one of the leaf-forms occurring in the second
population is genetically fixed. Gibberellic acid is able to
induce similar changes in leaf-form. A possible model for the
control of leaf-shape in the species is presented.
Some populations of P. glabrata are intermediate in their
morphology between P. glabrata and P. antarctica. Morphometric
analysis reveals three distinct aspects of variation in the complex.
The first differentiates P. glabrata from P. antarctica at low
altitudes. The second aspect demonstrates ecoclinal variation in
P. glabrata and is correlated with the severity of climate. The
third aspect involves a genetically maintained bimodal distribution
of leaf-shape within populations. The alternatives of introgressive
hybridization and disruptive selection as originating mechanisms
are discussed.
An experimental taxonomic investigation of the P. tasmanica -
P. daltonii corrtplex is made. Morphometric analyses suggest that
the taxa are largely distinct, although it is probable that
introgression has occurred.
Finally, a brief investigation of other taxa belonging to
Plantago section Mesembrynia is made. The study provides an
estimate of the level of diversification in the section, and
clarifies some aspects of the established taxonomic relationships
within the section.

Item Type: Thesis - PhD
Authors/Creators:Brown, MJ
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