The leafy liverworts are so-named because the gametophyte is more complex, consisting of branched, short, upright axes (stems) with very simple leaves. Rhizoids attach the gametophytes to the substrate. Approximately 4000 of the 6000 species of liverworts worldwide belong to this category. Although they are particularly abundant in the tropics and sub-tropics, they have an extensive distribution. Leafy liverworts are associated with either ascomycete or basidiomycete fungi.
In the associations between leafy liverwort species in the Jungermanniales and basidiomycete fungi, hyphae enter the tips of rhizoids, grow down the length of these structures, and then enter cells in the inner stem region where they form intracellular fungal coils. Often, wall depositions occur along the rhizoids; these may be a mechanism to prevent the ingress of pathogenic fungi. Uncolonized stem cells adjacent to those with intracellular coils form pegs of wall material that overgrow penetrating hyphae.
|
