ENTOMOPHILY IN THE DIOECIOUS GYMNOSPERM EPHEDRA APHYLLA FORSK. (= E. ALTE C.A. MEY.), WITH SOME NOTES ON EPHEDRA CAMPYLOPODA C.A. MEY. III. FURTHER ANTHECOLOGICAL STUDIES AND RELATIVE IMPORTANCE OF ENTOMOPHILY

ABSTRACT

Additional anthecological studies (phenology, insect visitors, pollen rain, and stickiness of the pollen on Ephedra aphylla are reported. A peculiar mode of growth of male specimens of E. aphylla is mentioned and its biological significance is briefly discussed. Among the visitors, representatives of certain groups of flies appear to be the most important pollinators, Hymenoptera taking a second place. The pollen rain of E. aphylla is already low at a distance of 15 m from the pollen source; the bulk of the pollen produced, if not removed by insects, is shed in aggregates of 2 to 600 grains and mostly falls down almost vertically in the dense thickets. In combination with the intermingled growth of male and female plants, this leads to gravitational pollination. The stickiness of the pollen is discussed in connection with the low rate of its dispersion by air currents, and a more direct method of assessment is suggested. The overall conclusion is that entomophily in some and conceivably in all Ephedra species is an established fact, also because of certain adaptations such as the stickiness of the (coherent) pollen grains; however, E. aphylla and possibly some or all of the other Ephedra species exhibit ambophily as well. By encasing female branchlets in gauze (so as to prevent insect visits), the relative importance of biotic vs. abiotic pollination was assessed by recording the rate of seed set. Our results suggest at least a partial dependence on entomophily for a maximum seed set. A certain dependence on biotic pollination in association with certain adaptive features (viz., either an incipient monocliny of the male strobili, or nectarial secretion in strictly diclinous forms) may be taken as a possible intermediate phase in the evolution from anemophily to entomophily and as a yardstick for the advent of biotic pollination among the earliest zoophilous angiosperms.