The unusual occurrence of tricolpate pollen within Mutisieae (Asteraceae)

Abstract

The monotypic genus <i>Hecastocleis</i> and species of <i>Ainsliaea</i> DC. (Asteraceae, Mutisieae) have tricolpate pollen, which is unusual in Asteraceae. The pollen morphology of <i>H. shockleyi</i> and species of <i>Ainsliaea</i> were studied with light microscope and scanning electron microscope. Pollen of <i>H. shockleyi</i> and some species of <i>Ainsliaea</i> have tricolpate aperture but differ in size and exine features. The pollen of Ainsliaea is bigger than that of <i>Hecastocleis</i>, and has more conspicuous microspines, a <i>Mutisia</i>- or an <i>Ainsliaea</i>-exine type, and is slightly thickened at the poles. The pollen of <i>H. shockleyi</i> is scabrate-microechinate with small puncta, and has the <i>Mutisia</i>-exine type, which is regularly thickened over the complete grain. The occurrence of tricolpate pollen supports previous studies that <i>Hecastocleis</i> and <i>Ainsliaea</i> stand apart from other genera of Mutisieae, but the occurrence of <i>Mutisia</i>-exine type does not suggest complete independence of the tribe.