The pollination of Chasmanthe and Crocosmia has not been much studied, and most of the observations here are original. The flowers of all three species of Chasmanthe have the characteristics of other African Iridaceae, and of plants in general, that are pollinated by sunbirds, species of Nectarinia (Goldblatt et al. 1999). They are orange to red, sometimes with green or yellow markings, and have an elongate tube, relatively wide and more or less tubular in the upper half and slender in the basal half. These flowers produce comparatively large quantities of nectar from septal nectaries, that is, nectar-secreting glands in the radial walls (septa) of the ovary. Nectar is secreted via small pores in the top of the ovary directly into the perianth tube, where it accumulates when the flowers are open. Nectar volumes of as much as 30 μl (microliters) have been recorded in Chasmanthe aethiopica . In general, nectars that flowers offer to birds have a relatively low nectar concentration, though there are some important exceptions, even within the family Iridaceae.
Chasmanthe species , however, do conform to this trend. Nectar concentrations of 10% sugar have been reported for C. bicolor , and 15.7-17% sugar for C. aethiopica and C. floribunda , levels that are consistent with bird pollination. Nectar sugar chemistry also reflects the bird pollination in these species, for the nectar of Chasmanthe flowers has high proportions of the so-called pentose sugars (glucose and fructose) and low levels of the hexose sugar (sucrose). Species of subfamily Crocoideae that are pollinated by bees, moths and long-proboscid flies invariably have nectars with higher sucrose concentrations: so-called hexose-rich or sucrose-dominant nectars in the terminology of Baker and Baker (1983).
Comparable nectar characteristics have been obtained for two bird pollinated Crocosmia species for which we have nectar data, C. fucata and C. paniculata . Flowers of C. fucata produce as much as 11.5 μl of nectar with an average concentration of 18.0% sugar, figures closely matched by those of C. paniculata , which has a nectar concentration of 17.
4%. Analysis of C. fucata nectar also shows unusually high levels of glucose and fructose (pentose sugars) and a sucrose: pentose ratio of 0.53, which is regarded as pentose rich (Baker and Baker 1983), a pattern consistent with bird pollination. The only other species of Crocosmia for which we have nectar data are C. aurea and C. pottsii . The nodding flowers or C.
aurea , evidently adapted for pollination by large Papilio butterflies, produce as much as 3.7 μl of nectar with average sugar concentrations for different population samples of 17.7-24.3%. The flowers of C. pottsii , which appear to be adapted for pollination by bees, have an average sugar concentration of 23.2%. No data are available for nectar sugar chemistry.
The relatively low sugar concentration in C. aurea nectar is typical of butterfly-pollinated flowers. Chasmanthe species have long been considered to be pollinated by sunbirds, and the first such published observations date from the late 19th century when the pioneer pollination biologist George Scott Elliot (1890) recorded visits by the lesser double-collared sunbird, Nectarinia chalybea , to C. aethiopica . The same species of sunbird was observed visiting C. aethiopica by Vogel (1954) and Goldblatt et al. (1999), the latter also reporting visits by the malachite sunbird, N. famosa , to a second population.
Visits by the lesser double-collared sunbird to C. floribunda have also been recorded. Pollination observations for a few Crocosmia species by sunbirds are available (Goldblatt et al. 1999), and not surprisingly these few species have flowers very much like those of Chasmanthe species. In the Drakensberg, the malachite sunbird has been noted visiting Crocosmia pearsei , and the double-collared sunbird, Nectarinia afra , has been observed visiting C. paniculata near Graskop in Mpumalanga province. The Namaqualand C. fucata is also pollinated by malachite sunbirds.
The only known visitor to the narrow-tubed flowers of Crocosmia aurea is the large swallowtail butterfly, Papilio nireus . Examination of C. aurea flowers shows that only insects with long, slender mouthparts can reach the nectar because the bases of the three filaments partially block the mouth of the tube, leaving three tiny channels between the filament bases that permit entry to the tube, which may be as long as 11/16 inches (27 mm). A butterfly hangs upside down on the nodding flowers and inserts its slender proboscis into the tube while grasping the tepals with its legs. We suspect that flowers of C. masoniorum are likewise pollinated by large butterflies, for like C. aurea it has a relatively short, narrow perianth tube, spreading tepals and well-exserted stamens, thus broadly resembling those of C. aurea except that they are held erect instead of nodding.