Abstract:
Ekebergia capensis is a medium-sized to large evergreen to deciduous tree ranging
from southern Africa to Ethiopia. Two morphologically-distinct variants of E.
capensis, southern and northern, may be recognized in southern Africa. Despite
its wide distribution range there appear to be no published reports on the
secretory structures occurring on the leaves. In very young leaves, colleters on
the petiolules, adjacent portions of the rachis and the midrib of the adaxial leaflet
surfaces, secrete fluid which at least partly covers these developing areas. This is
the first record of colleters in Meliaceae. In addition, several extrafloral nectaries
(EFNs) are found in variable positions on the abaxial side of the leaflets. No
stomata are associated with the EFNs. The glandular tissue of active EFNs is
surrounded by druse crystals of calcium oxalate and consists of secretory cells
some of whose walls are separated by “strands” of amorphous lipophilic
material, especially in a radial orientation. EFNs on developing leaves are
inconspicuous but with time, frequently become more easily visible due to the
accumulation of pinkish/reddish anthocyanins. Even on senescent leaves, shed in
autumn, large droplets of nectar are frequently visible on the EFNs. The
secretory tissue originates from protoderm and ground tissues. Slight differences
in abundance, size, shape, position and structure exist between the EFNs of the
southern and northern forms. Varying proportions of glucose, fructose and sucrose were detected in the rather viscous nectar with the most abundant sugar
usually being fructose. Ants were only rarely observed feeding on the nectar.
This finding is in conflict with the generally accepted idea that EFNs provide
food for ants which in turn protect the plant from herbivores. More detailed
studies of the chemistry of the nectar, which is relatively copious, may provide
clues as to the function.
