University of Tasmania
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Studies of variation in some Tasmanian species of Plantago L.

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posted on 2023-05-27, 06:29 authored by Brown, MJ
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 iv 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. v 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.


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