Reproductive phenology, pollination biology, and gynoecium development inDiscaria americana(Rhamnaceae)

Abstract

Discaria americana individuals bloom in late winter or early spring and display large numbers of small, white, entomophilous flowers for about a month. Individual flowers contribute to colour display for c. 4 weeks, although they are active in pollen transfer only 5-7 days (male phase = days 1-3, female phase = days 2-5). A strong, foetid smell along with nectar and pollen attract over 50 insect species, of which 19 are probable pollinators. These are mainly Diptera, but include as well Hymenoptera-Apoideae and Coleoptera. Incomplete protandry and reverse herkogamy restrict pollen-stigma interference, but self-incompatibility seems operative in avoiding self-fertilisation. Gynoecium development (from carpel inception to fruit dehiscence) lasts c. 18 weeks, starting with a 33-day-long prefloral period during which most gynoecial structures arise. The floral and postfloral phases occupy c. 18 and 73 days, respectively. The times of starting and ending of several growth processes were determined. Minimum growth rate of the ovary coincides with the active period of the flower, after which some, presumably fertilised, flowers resume ovary growth whereas other ones begin to wither. Pedicels of young fruits become erect which could be beneficial both for seed filling and explosive dispersal. Endocarp maturation apparently sets an upper limit on seed expansion and, indirectly, on size increase of the fruit. Early flowering and erect pedicels are apparently derived traits within Discaria.