Sex choice and the size advantage model in jack-in-the-pulpit (Arisaema triphyllum).

Arisaema triphyllum is a perennial herb whose sex and size often change from one growing season to the next. The proportional gain in reproductive success (RS) with size is much greater for female (carpellate) plants than it is for male (staminate) plants. I constructed RS-size curves for males and females; the curves intersect at a point t = 398 mm. According to theory derived from the size advantage model, t is the point below which the plants should be male and above which they should be female. Plots of size-frequency distributions of males and females show that below 380 mm the proportion of males is greater than the proportion of females, whereas above that point the proportion of females is greater than the proportion of males. Thus prediction and observed results are in very close conformity.