Pollen Morphology in Tribe Lactuceae (Compositae)

The Lactuceae contain two basic pollen types, echinolophate and echinate. Most taxa have echinolophate, tricolporate pollen. Internally, most ektexines are composed of a perforate spiny tectum, several levels of columellae, a cavus, and a foot layer. In lacunae, the columellae are reduced to a single level and the cavus is often absent. Highly modified echinolophate pollen grains are found in Scolymus, Scorzonera and Tragopogon. Scolymus, Catananche, Scorzonera, and Tolpis have distinctive exine stratification patterns. Exines of Catananche and, to a lesser extent, those of Tragopogon contain internal foramina like those found in the Heliantheae. Echinate pollen is found in all subtribes and is probably ancestral. However, some echinate grains are probably derived.