STARCH IN ANGIOSPERM POLLEN GRAINS AND ITS EVOLUTIONARY SIGNIFICANCE

Abstract

Pollen grains of 990 species were examined and measured to test four predictions: (1) “Primitive” angiosperms will have starch‐containing pollen; more advanced families will have starchless pollen. (2) Where Hymenoptera and Diptera use pollen nutritionally, there will be selection of starchless (oilcontaining) pollen, particularly where pollen is the only reward for visitors. (3) Conversely, in autogamous species, anemophilous species, and those pollinated by Lepidoptera or birds, the energetically more economical accumulation of starch will be seen. (4) Small pollen grains will be more likely to be starchless (oil‐rich); starch‐containing grains will tend to be larger. Prediction 1 is only partially supported by the results; contemporary representatives of primitive families often show starchless grains, and so do most “advanced” families. Strong intra‐familial resemblances are found (and some between groups of families), but other families show mixtures of “starchy” and “starchless” species. The latter are more likely to show a fit between food reserve and pollination system. Prediction 2 is well supported. Prediction 3 is supported in that autogamous and anemophilous species show relatively high proportions of starchy grains, but the picture is complicated for them by apparent selection for starchlessness (oil‐richness) in small pollen grains (prediction 4), and for the lepidopteran‐ and bird‐pollinated species by selection for large starchless (or very large starchy grains) in species whose pollen tubes must traverse long styles.