Pollen morphology of Linum L. section Syllinum Griseb. (Linaceae) of Turkey

Abstract This study presents the pollen morphology of 16 taxa of Linum L. section Syllinum Griseb., 13 of which being endemic to Turkey, by using light and scanning electron microscopy. All the pollen grains are trizonocolpate; however, some taxa were observed to have also hexacolpate grains along with trizonocolpate ones. The pollen grains are large, suboblate, less often oblate spheroidal in shape. Distyly is predominantly present in the section, except for homostylous species Linum nodiflorum L. All the studied distylous taxa have dimorphic pollen grains. In short-styled floral morphs, the exine has monomorphic processes, gemmae, which at the top have a ring of marginal papillae, with or without prominent central papilla. In long-styled floral morphs and in homostylous morph, the exine is dimorphic and has two types of processes: bacula, smaller in diameter, ending in a central microechinus, and clavae, larger in diameter with a central microechinus ending into lobes or a ring of scabrae at the margins. In the studied distylous species, the pollen of short-styled morphs is larger than that of the long-styled morphs. Based on the morphometric data, the principal component analysis has grouped these two morphs separately; with the homostylous one, although with dimorphic exine, nested within the short-styled morphs. This could be considered as evidence supporting the loss of heterostyly in homostylous Linum.