Reproductive biology of four weedy Euphorbia species from Ile-Ife, Nigeria

Abstract

Euphorbia heterophylla Linn., Euphorbia hirta Linn., Euphorbia hyssopifolia Linn. and Euphorbia prostrata Linn. are four noxious, yet economically important weeds, useful as phytomedicine in some parts of the world and also in Nigeria. Studies were carried out on their reproductive biology with a view to understanding the mode of their spread. Parameters investigated include number of days to seedling emergence, germination
percentage, number of days to flowering, period to anthesis, pollinators, pollen viability, pollen size, floral structure, fruits type, seeds type, average number of fruit per plant, average number of seeds per plant and mode of seed dispersal. Results obtained showed that the seedlings of the four Euphorbia species studied emerged within 3 to 5 days; numbers of days to 50% flowering took 44 to 58 days; while flowering and fruiting continued
throughout the remaining part of the year; thus exhibited r-strategy, expending more time and allocation of resources on their reproductive phases than their vegetative phases. Also differences existed in their stigma shape, perianth colour, perianth texture, pollen sizes, pollen viability as well as ripened colour of seed which were all significant characters that could be useful in delimiting the species. Furthermore, the study revealed that the
four species were essentially insect pollinated and their seeds dispersed by means of explosive mechanism usually characteristic of their schizocarpic fruits. This ability as well as their tendency to exhibit r-strategy could probably account for their ability to spread and invade cultivated fields, waste lands and roadsides.

Keywords: Explosive mechanism, r-Strategy, Seed dispersal, Pollen viability, Seed set