Critical plant size for flowering in biennials with special reference to their distribution in a sand dune system.

Four biennial species (Oenothera erythrosepala, Dontostemon dentatus, Erigeron strigosus, and Erigeron sumatrensis) from the dune system at Azigaura, Japan, were sand-cultured in pots with different nutrient levels, and the critical plant size for the development of a flowering stalk was determined. The critical size decreased in the order O. erythrosepala>E. strigosus>D. dentatus=E. sumatrensis, and corresponded to the order of their distribution along the gradient of soil fertility in the dune system. This correspondence is discussed, and it is concluded that in a less fertile environment, biennials producing seeds after attaining a larger size have an advantage over those producing seeds earlier.