Developmental morphology of ovules and seeds of Austrobaileyales

Abstract

Development of ovules of 'Illicium anisatum' (Illiciaceae), 'Trimenia moorei' (Trimeniaceae), and 'Austrobaileya scandens' (Austrobaileyaceae) (Austrobaileyales) was observed. In 'Austrobaileya scandens' and 'Trimenia moorei' the outer integument is hood-shaped, while it is cup-shaped in 'Illicium anisatum'. On the basis of a phylogeny, the ovule with the hood-shaped outer integument is suggested to be primitive in Austrobaileyales. Seed development of Austrobaileyales was also examined. In 'Austrobaileya scandens' the seed is mesotestal, ruminated, not pachychalazal, and has a micropyle–hilum complex. In 'Trimenia moorei' the seed is exotestal, perispermous, not pachychalazal, and has a micropyle–hilum complex and a circular cap. The seed of 'Illicium anisatum' is exotestal, not pachychalazal, and has a circular cap. Taking the character states of other basal angiosperms into account, primitive seeds of angiosperms are inferred to have such characters as the unilayered exotestal mechanical tissue, circular cap, micropyle–hilum complex and non-pachychalazy. The inferred primitive seed is very simple, suggesting that a great diversity of seeds is established through elaboration of organs/tissues of seeds, and not through reduction as hypothesised previously.