Andromonoecy and Fruit Set in Leptospermum myrsinoides and L. continentale (Myrtaceae)

Abstract

Leptospermum myrsinoides and L. continentale (Myrtaceae) are andromonoecious. All flowers of these species are potentially bisexual in function and male flowers result when pistil development ceases after floral initiation. All male flowers possess vestigial pistils. The proportion of male flowers within three populations was recorded over three seasons. In both species, the proportion of male relative to bisexual flowers increased as the flowering season progressed. A strong relationship exists between flower sex and branch position, with bisexual flowers tending to occur on upper and outer positions on plants. Fruit set is not limited by pollination but by some other resource, possibly nutrients. Whilst andromonoecy sets the upper Limit of the number of fruit which may be formed, the number of fruit set on a plant is always less than the number of bisexual flowers. It is suggested that andromonoecy in L. myrsinoides and L. continentale is an evolutionary response to low resource availability allowing optimal resource allocation to reproduction in these species.