Growth and Reproductive Phenology of Welwitschia Mirabilis Hook. F.

Reproductive phenology, reproductive traits and the pre emergent reproductive success (PERS) of Welwitschia mirabilis were studied in plants growing in the Botanical Garden of Portici. The leaves grow throughout the year and growth is positively correlated to temperature and day length; at flowering, the growth rate slows down. The plants have a reproductive cycle lasting 9-10 months; male plants form more branches and strobili than females, female strobili are larger than male ones. Both male and female plants produce cones that differ in the color of the covering bracts. Plants produce a lot of seeds, but most of them are empty; therefore the seed/ovule ratio is low. Filled and empty seeds are morphologically similar; filled seeds have high vitality that is maintained for several years. As probable causes of the low seed/ovule ratio, both pollination and embryo abortion are taken into account; our observations lead us to believe that the embryo abortion hypothesis is more accurate. However, since each plant may produce a discrete number of cones and filled seeds are highly viable, ultimately Welwitschia appears to be a rather efficient plant in terms of pre emergent repro- ductive success.