Seed heteromorphism, or the simultaneous production of multiple distinct seed morphs, is widely assumed to serve as a bet hedging strategy to cope with unpredictable environmental variation. Furthermore, it is predicted to occur more commonly among plants of annual duration. Our aim was to test both predictions. First we summarized the occurrence of seed heteromorphism among angiosperms in southwestern North America through a literature review. We documented all heteromorphic species as well as all homomorphic species contained in genera composed of at least one heteromorphic species. Next, through spatial analysis, we compared the occurrence of all seed hetero- and seed homomorphic plants with respect to aridity, a measure of environmental unpredictability for plants. For all the plants we documented, we also recorded their duration and weediness for assessment with respect to seed heteromorphism and homomorphism.
Results/Conclusions
In our literature search we found 170 species of seed heteromorphic plants spread across 63 genera and 11 families. Seed heteromorphism was concentrated in the Asteraceae and Boraginaceae which contributed 121 and 32 species, respectively. In comparison to their seed homomorphic counterparts, seed heteromorphic species were not significantly more prevalent in arid regions nor more likely to be of annual duration as was predicted by bet hedging theory.