Pollen morphology of the Amborellaceae and Hortoniaceae (Hortonioideae: Monimiaceae)

Abstract

Amborella trichopoda Baillon is a vesselless New Caledonian endemic in a family of its own, the Amborellaceae. Pollen is boat-shaped-elliptic to subglobose and small to medium sized. It is mono-aperturate, heteropolar, with the aperture probably at the distal pole (anaulcerate to anasulcate) or apolar and inaperturate. Inaperturate pollen appears to have evolved incompletely in Amborella. The exine has ornamentation of a gemmate-like appearance but consists of small cupules constructed of coiled cylindrical strands (ca. 100–130 nm diameter), bearing small spines. The sexine is ca. 0.5–1.0 μm thick and overlies a foot layer 0.2–0.4 μm thick. An endexine is absent. The intine has an outer zone containing tubular material within and adjacent to apertures. Pollen morphology supports the retention of the Amborellaceae as a separate family, within the Laurales. Hortonia is a Sri Lankan endemic of 3 species comprising the Hortoniaceae or subfamily Hortonioideae of the Monimiaceae. Pollen is inaperturate (omniaperturate), isopolar, spherical, small to medium-sized, with hemihelical bands of exine thickening radiating from two “poles”. Each band is constructed of interwoven cylindrical strands ca. 80–200 nm diameter. This unusual exine has no tectum, columellae, foot layer or endexine. Between and beneath the exine bands there is a thick intine with an outer zone containing tubular material. Pollen morphology of Hortonia emphasises its isolated position but also suggests links between the Lauraceae and Monimiaceae.