Selective forces in the emergence of the seed habit
Article first published online: 14 JAN 2008
Biological Journal of the Linnean Society
Volume 38, Issue 3, pages 215–238, November 1989
How to Cite
HAIG, D. and WESTOBY, M. (1989), Selective forces in the emergence of the seed habit. Biological Journal of the Linnean Society, 38: 215–238. doi: 10.1111/j.1095-8312.1989.tb01576.x
- Issue published online: 14 JAN 2008
- Article first published online: 14 JAN 2008
- Received 10 May 1988, accepted for publication on 10 February 1989
- seed habit
The evolution of the seed is one of the major events in the history of land plants. In this paper, we consider the suite of characters that define the seed habit, and discuss the probable selective pressures that produced each character. Our major conclusion is that most characters are a direct consequence of the origin of heterospory and of natural selection for propagules with larger food reserves.
Seeds are traditionally defined by the possession of integuments. However, some heterosporous pteridophytes possess integument-like structures. Therefore, integuments cannot explain the evolutionary success of seed plants. Rather, we believe that the decisive character in this success is related to pollination. Seed plants differ from other heterosporous lineages in the capture of microspores before dispersal of the 'megaspore'. Modern gymnosperms all possess mechanisms whereby the maternal sporophyte withholds resources from potential propagules that have not been pollinated and/or fertilized. This represents an increase in efficiency over Pteridophytic reproduction. Wind-pollination means the propagule is vulnerable to pathogens that mimic pollen, and pathogen pressures may have contributed to some seed characters.