Floral functional structure, sexual phases, flower visitors and aspects of breeding system in Roella ciliata (Campanulaceae) in a fragmented habitat

Abstract

Continued habitat destruction in lowland areas of the Western Cape, South Africa, due to urbanization has reduced Roella ciliata to a few isolated populations and it is unknown whether this endemic shrublet will persist. Here, we examine the reproductive biology of a small population of R. ciliata occurring in a residential nature reserve 30 km east of Cape Town to provide baseline information for future studies. Data were recorded on the functional structure of the flower, duration of the morphological gender phases, floral visitor profile and the relationship between breeding system and habitat. Observations revealed that this species possesses reproductive characteristics typical of Campanulaceae such as dichogamy, protandry and secondary pollen presentation via pollen collecting hairs. Floral longevity ranges between 1 and 3 days. Anthesis occurs in synchronicity at 0700 hours and individual flowers close between 0930 and 1500 hours daily. The staminate phase lasts between 2 and 29 h and is significantly influenced by the removal of pollen by floral visitors, while the pistillate phase lasts between 21 and 69 h. R. ciliata maintains a generalized, entomophilous pollination system although floral visitors are generally scarce. Despite some intraspecific variation, the pollen/ovule ratio indicates that R. ciliata has a facultatively autogamous breeding system, in contrast to its floral attributes which might favour xenogamy. This reproductive mechanism may ensure survival under these habitat conditions and could represent a shift from outcrossing to selfing at the cost of reducing genetic variation over time.