Liverworts or the Jungermanniophyta


Whereas the mental image of mosses conjure up the thought of green carpeted boulders framing the banks of a swiftly moving creek, liverworts remind of less delectable offerings

Reality of liverworts...

Liverworts can be thalloid, (flattened ribbons of green tissue) Or foliose with 'leaves' attached to a stem.

  • The foliose liverworts are actually by far the largest group of liverworts. In the Neotropics, they contain about 1000 species or 80% of the entire liverwort flora
  • Liverworts of this group bear delicate leaf-like structures, on a branched or unbranched stem, which most often lies horizontally or parallel with respect to the surface upon which the plant is growing.
  • The leaves are generally only a single cell thick, and have no vascular system and no protective surface layer or cuticle.
  • Often the leaves are divided into two or more lobes, and sometimes the lobes are folded to form various shapes.

The leaves are most often arranged in two rows, but in many species there is a third spiky row of very much smaller leaves.

leafy form to the left and thallose Marchantia above

In thallose liverworts the plant body has no stem-leaf structure, but consists instead of a "thallus" - a more-or-less flattened tissue, one to several cells thick. The thallus may be subdivided into lobes,and these may vary in width from 2-3mm to 1cm or more according to species. In some species there is a thickened midrib, and some may have pores (small holes) dotted about their surface.

Habitat: Some liverworts are not resistant to desiccation whereas others can withstand prolonged periods of dryness.

Among those resistant to desiccation is the widely distributed Marchantia which has developed physiological and also morphological adaptations to withstand extended periods of dryness.

The capsules of liverworts are simpler in structure than those of mosses, consisting usually of a simple sphere which releases spores by splitting longitudinally into four sections. In liverworts, the seta only elongates when the capsule is ripe, and the rate of elongation is relatively rapid (the photograph shows a ripe liverwort capsule with a seta in the process of elongation). Liverwort photograph by Brian Steer.

 

To help disperse their spores (without the aid of the peristome we saw in the mosses), liverworts may have elaters, which are hygroscopic and expand out when conditions the humidity becomes drier. After all you don't want your spores to come out when it rains... not great for dispersal.
Their springing action carries the spores into the air..I'm not sure if this is a great analogy, but think of those trick cans, which when an unsuspecting victim opens up the lid, 'worms' or something grosser come popping out.

One of the striking features of the hepatics is the presence of oil bodies in their cells. They have different shapes, colors and vary in number

Liverwort photograph by Brian Steer.

Oil bodies contain terpenoids that sometimes give the plant a particular scent. These secondary compounds which we will study in greater detail under medicinal botany, play several roles as herbivory deterrents and attractants in the higher plants.

It has been suggested that oil bodies may serve liverworts to withstand periods of dryness and to deter herbivores. Any thoughts on other functions?

Some of these terpenoids contained in the oil bodies are biologically active substances and can cause allergenic reactions, while others are cytotoxic, have anti tumor activity in rats (e.g., for lymphocytic leukemia) or tumor-promoting activity, vasopressin antagonistic reactions and antifungal activity among others

This material should remind us that much of evolution is biochemically based, and organisms that appear as 'simple' morphologically may have in truth quite complex chemical systems within.

 

Life cycles and features of the Bryophytes

The mosses

The liverworts

The hornworts

Economic and ecological roles of the bryophytes

Differences between the mosses and liverworts

Return to introductory Bryophyte page