Multiple lines of evidence confirm predicted moth pollination of the fragrant, foliage-coloured Cape orchid Satyrium odorum

Abstract

• Satyrium odorum was the first African orchid thought to be sunbird-pollinated • Floral traits including colour and scent are more consistent with moth pollination • Multiple lines of evidence revealed pollination by small settling moths • Flowers produce a blend of aromatic scent compounds in the evening • Previous observations were thus of nectar thieving visits by sunbirds Floral traits are often indicative of the functional pollinator group to which plants are adapted, but exceptions occur and require further investigation. Here I revisit a previously published observation of visits by sunbirds to the foliage-coloured and fragrant flowers of the South African orchid Satyrium odorum . Floral visitor assessments based on both direct observations and camera trapping revealed small settling moths as the exclusive visitors, several of which carried pollinaria on their proboscis. Pollinarium removal was exclusively nocturnal, coinciding with emission of a blend of aromatic scent compounds that are generally associated with moth pollination. In contrast to many species that are known to be bird-pollinated, flower colour of S. odorum was greenish-yellow and is therefore unlikely to function in pollinator attraction. Pollination rates and pollen transfer efficiency were both comparatively high compared to other Satyrium species. Together, these complementary lines of evidence confirmed that the previously observed visits to S. odorum by sunbirds, which are known to groom pollen off, were likely opportunistic and may not result in effective pollination. Instead, together with several distantly related co-flowering plant species with similarly cryptically coloured, evening-scented flowers, S. odorum likely belongs to a guild of fynbos species with flowers that are adapted for pollination by nocturnal moths.