First report of moth pollination in Struthiola ciliata (Thymelaeaceae) in southern Africa

Abstract

Struthiola ciliata (L.) Lam., an ericoid shrub widespread in fynbos vegetation in the southwestern Cape, displays the floral syndrome associated with pollination by settling moths. Flowers, which are produced throughout the year, are creamy white in colour, with a slender hypanthium tube ± 20 mm long. The anthers are included within the tube and the mouth of the tube is surrounded by eight fleshy petaloid scales. Anthesis takes place in the evening at ± 18h00, at which time the flowers begin to emit a strong, sweet, spicy and somewhat coniferous fragrance from the petaloid scales. The compounds thujone, isothujone, verbenone, α-terpineol, benzyl acetate, eugenol and vanilline are the main components of the scent profile detectable by the human nose. The cells of the petaloid scales are densely cytoplasmic and contain numerous oil droplets. Starch-rich tissue is located near the mouth of the hypanthium tube. Flowers accumulate small volumes (0.025–0.188 μl) of moderately concentrated nectar (20–34% sucrose equivalents) in the hypanthium tube. Individual flowers last for 9 to 11 days, with nectar secretion restricted to the first 3 to 4 days. The only floral visitors observed were the moths Syngrapha circumflexa (Linnaeus) and Cucullia terensis (Felder and Rogenhofer) (Lepidoptera: Noctuidae), which visited the flowers at dusk and early evening, confirming that the species is moth-pollinated.