Spore wall ultrastructure in the liverwort Fossombronia longiseta

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Abstract
Mature spores of Fossombronia longiseta (Metzgeriales, Codoniaceae) were examined with both scanning and transmission electron microscopes. Sporoderms are highly sculptured. The distal face markings consist of parallel ridges (cristae) or spines. The flattened proximal face has a series of short spinelike cristae, and a triradiate ridge mark sometimes is apparent. In section, the sporoderm consists of an intine and a two-layered exine. The inner exine layer consists of two lamellae, each of which contains a series of long, thin (3–4 nm), closely spaced, electron-lucent subunits; the subunits are separated by electron-dense material. The more or less solid outer exine consists of highly irregularly shaped lamellae, which also have a "white line" component. Amorphous, electron-dense material permeates these lamellae and fills the channels between the lamellae. The intine and much of the electron-dense material of the exine is removed by acetolysis. Spore wall ultrastructure in this species is complex compared with other species of the Metzgeriales and Jungermanniales that have been studied so far.