Andromonoecy in Four Australian Species of Leptospermum

Abstract

Leptospermum myrsinoides, L. juniperinum, L. laevigatum and L. lanigerum are recorded as being andromonoecious, with the proportion of total flowers that is functionally male averaging 36, 42, 48 and 14% respectively at Wilson's Promontory during the 1981-83 flowering seasons. For each species, this figure varied markedly between individual plants, sites and seasons: for example, for L. myrsinoides it ranged from 0 to 80% among individual plants at one site on one occasion, from 31 to 71% at one site over three seasons, and from 31 to 71% at different sites during the one season. This variation is consistent with the view that andromonoecy enables plants to regulate their sexual expression according to changing environmental conditions. Rates of insect predation of male flowers (usually 52%) were consistently lower than those of bisexual flowers (usually 5-10%) and in L. myrsinoides there was a negative correlation between the rate of predation of bisexual flowers and the proportion of total flowers that was male. A hypothesis is proposed that a benefit of andromonoecy is the satiation of flower predators.