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The qualitative and quantitative studies, presented in this article, on wood anatomy of various species belonging to ancient Magnolia genus reveal new aspects of phylogenetic relationships between the species and show evolutionary trends, known to increase fitness of conductive tissues in angiosperms. They also provide new examples of phenotypic plasticity in plants. The type of perforation plate in vessel members is one of the most relevant features for taxonomic studies. In Magnolia, until now, two types of perforation plates have been reported: the conservative, scalariform and the specialized, simple one. In this paper, are presented some findings, new to magnolia wood science, like exclusively simple perforation plates in some species or mixed perforation plates – simple and scalariform in one vessel member. Intravascular pitting is another taxonomically important trait of vascular tissue. Interesting transient states between different patterns of pitting in one cell only have been found. This proves great flexibility of mechanisms, which elaborate cell wall structure in maturing tracheary element. The comparison of this data with phylogenetic trees, based on the fossil records and plastid gene expression, clearly shows that there is a link between the type of perforation plate and the degree of evolutionary specialization within Magnolia genus.
The ratio of primordium size to the meristem size (P/M ratio) is regarded by some geometrical models of phyllotaxis as the parameter, which determines the quality of spiral and whorled patterns of lateral organ arrangement. This assumption was tested on floral meristems in four genets representing four Magnolia taxa: M. × salicifolia, M. stellata, M. denudata and M. acuminata. In successive zones of Magnolia flower, lateral organs are initiated in specific phyllotactic patterns and at specific values of the meristem and primordia sizes. The elements of perianth, usually positioned in three trimerous whorls, are initiated as large primordia on relatively small meristem. The switch in the identity of primordia, from tepals to stamens is accompanied by an abrupt increase in the size of the meristem and decrease in the primordia size. Small values of P/M ratio and frequent occurrence of qualitative transformations of phyllotaxis contribute to the exceptionally rich spectrum of spiral patterns in androecium zone. New spiral patterns emerge when bigger primordia of carpels are initiated on the meristem, which at the same time starts diminishing in size either abruptly (M. × salicifolia, M. stellata, M. acuminata) or slowly (M. denudata). Spiral patterns identified in gynoecia have lower numbers of parastichies than the patterns of androecia and occur in frequencies specific for the genet. Although noted ranges of the meristem and primordia sizes, justify the occurrence of phyllotactic patterns observed in successive zones of Magnolia flower, they do not explain genet-specific frequencies of the patterns observed in gynoecium zone. The lack of straightforward relationship between frequency of the patterns and P/M ratio in gynoecium suggests that more complex geometrical factors or factors of non-geometrical nature are engaged in determination of Magnolia floral phyllotaxis.
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