A palynological study of the Liabeae (Asteraceae) /

Abstract

Surface features and internal structure of the spines in the pollen of the Liabeae are illustrated by scanning electron microscopy and drawings made from oil immersion light microscopy.Obser- vations are presented for all 16 genera of the tribe, Paranephelius and Pseudonoseris of the Paranephelinae, Astroliabum, Bishopanthus, Cacosmia, Chionopappus, Ferreyranthus, Liabellum, Liabum, Microliabum, Oligactis, and Sinclairia of the Liabinae, and Chrysactinium, Erato, Munnozia and Philoglossa of the Munnoziinae.No examples of echinolophate pollen are found in the tribe, but irregular groupings of spines are found to be characteristic of all but Munnozia and Chrysactinium in the Munnoziinae and Paranephelius and Pseudonoseris in the Paranepheliinae.The distribution of caveate forms in the Liabeae is clarified.The presence of a large cavus-like space interrupted by thin basal columuellae is confirmed in the genus Paranephelius, correcting early observations showing the genus as an exception to the basic uniformity of exine structure in the tribe.However, subcaveate forms have been discovered in the tribe in the genus Munnozia.SEM study of broken tecta in the genus Munnozia show previously unsuspected great potential for variation between closely related species and species groups.The structure of the exine supports views derived from floral structures regarding relationships with other tribes.No support is seen for a phyletic position near the Senecioneae, and closest similarity is seen to the Vernonieae.A basic difference is discovered in the arrangement of the basal columellae between the Liabeae and the Vernonieae, being clustered or forming a hollow cylinder under each spine in the former but forming a single solid basal columella under each spine in the most nearly comparable members of the latter.Genera of the Vernonieae shown for comparison include the non-lophate Blanchetia, Pseudostifftia, and Vernonia, and the lophate Bishopalea, Heterocypsela, and Phyllocephalum.