SECTION 8 



CYTOTAXONOMY AND EXPERIMENTAL TAXONOMY 



8.1. Cytology, Morphology, and Evolution in the 

 Proteaceae. L. A. S. Johnson and Barbara 

 G. Briggs (Sydney, Australia). 



The Proteaceae have a predominantly South- 

 ern Hemisphere distribution, in Australia, Africa 

 and South America, extending into both eastern 

 and western tropics. A fairly complete survey, 

 chiefly at the generic level, suggests that the 

 "Proto-Proteaceae" had 7 pairs of large chromo- 

 somes, as found today in Placospermum, Persoo- 

 nia, and Garnieria. Reduction to 5 pairs of 

 moderate size is represented in Bellendena, 

 with subsequent tetraploidy to 10 pairs in 

 Symphionema. In the remainder of the family, 

 ancestral doubling of the original 7 is indicated; 

 all of these genera have very much smaller 

 chromosomes, n = 14 occurs in both subfamilies 

 Proteoideae and Grevilleoideae, but repeated and 

 independent reductions to « = 13, 12, 11 and 10 

 appear to have taken place. So far as known, 

 numbers within genera are constant, except for 

 one case of tetraploidy (Persoonia) and one of 

 aneuploid increase (Orites, n = 14, 15). The 

 changes in chromosome number and size appear 

 to have occurred at early stages in the evolution 

 of the family. 



Comparative study of all morphological fea- 

 tures, together with cytology, has made it possible 

 to reconstruct the probable ancestral conditions 

 for the family and for its various subgroups -a 

 condition most nearly represented today in the 

 relict Placospermum (N.E. Queensland). A scheme 

 of relationships and evolutionary trends has 

 been worked out, taking into consideration 

 adaptive changes in relation to habitat, polli- 

 nators, and distribution. A tropical origin is 

 probable, with the temperate members in Austra- 

 lia and South Africa independently derived from 

 tropical sources, although the phytogeographic 

 history is complex. 



See Austr. Journ. Bot. 11, No. 1, in press. 



8.2. The Role of the Plastome of Oenothera in Evolu- 

 tion. W. Stubbe (Cologne, Germany). 



Cleland (1957, 1958) has elaborated the out- 

 lines of the phylogenetic relationship between the 

 complex heterozygotic races of the subgenus 

 Euoenothera and their homozygotic ancestors. 

 The diversity of species was derived from three 

 fundamental groups of complexes carrying, 

 respectively, the genes for (a) the hookeri- 

 strigosa-phenotype, (b) the grandiflora-biennis- 

 phenotype and (c) the argillicola-(3 parvi-flora- 

 phenotype. 



Independent investigations of Stubbe (1959) 

 demonstrated that the same major groups of 

 genome complexes stand out when attention is 

 confined to the co-operation between genomes 

 and plastomes. Five plastid types can be identified, 

 their distribution being of systematic importance. 

 On the basis of recent results the following facts 

 can be established about the role of the plastome 

 in evolution: 



1. All known kinds of damage to the normal 

 plastid development lead to a negative selection. 

 Sometimes these damages arise by spontaneous 

 mutation, but more frequently we find them after 

 interspecific hybridization. Since the pollen 

 contributes plastids to the zygote, though less 

 than the egg cell, we get a somatic segregation- 

 pattern of different plastid phenotypes, these 

 being green or chlorophyll-deficient, depending 

 on a good or bad compatibility between genome 

 and plastome. The viability of such chimaeras 

 depends upon the size of their green foliage 

 portion. 



If not only one but both kinds of parental 

 plastids are incompatible with the hybrid 

 genotype, the plastid differences result in a barrier 

 for hybridization, i.e. a factor establishing 

 isolation. Such plastome-dependent incompatibil- 

 ity has been demonstrated in crosses between the 

 homozygous species of the hookeri-, elata- and 

 grandiflora-group on one hand and the argilli- 

 cola-group on the other. 



2. In hybrids in which the genetically different 

 plastids of both parents develop normally, there 

 will be an invisible somatic segregation-pattern. 

 Concerning evolution, another factor brings its 

 influence to bear, namely plastid competition 

 (Schotz, 1954). This is due to differences in the 

 multiplication rates of the plastid types taking 

 effect in the "mixed" cells. If outcrossing is 

 guaranteed, repeated mixing of the different 



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