Plant of the Week
Marchantia (Marchantia polymorpha L.)
By David Taylor
Marchantia is a member of the Marchantiaceae, the Marchantia family. This family is one of many thalloid liverwort families. A thalloid liverwort is strap-like and often forms large colonies on the surface on which it grows. A liverwort is nonvascular green plant. It does not have phloem and xylem like ferns, conifers and flowering plants to transport water, food and minerals through the plant. As a result, liverworts tend to be small, only a few cells thick and grow in moist locations or in locations that dry out, but receive a lot of precipitation or fog. Many species of liverworts are found in the U.S. and Canada. Marchantia is among the largest and is often used in biology labs.
This species hugs the substrate on which it grows, usually moist soil or wet rocks. The thallus segments are dichotomously branched (continually branched in two branches) and are green to dark green. The segments are 10 to 15 millimeters (0.4 to 0.6 inches) wide, and frequently form large mats. Inspection with a hand lens will reveal that the surface of the thallus is covered with tiny pores. These are holes to allow gas exchange between the inside of the thallus and the atmosphere. Frequently, small saucer-like structures can be found inside of which are small green lentil-shaped objects. The saucer is a gemma cup and the lentil-shaped objects are gemmae. Gemmae allow the plant to reproduce asexually. Each gemma is capable of growing into a new thallus if the conditions are correct. Rain drops, insects, and small mammals all can spread the gemmae in the environment.
Occasionally, one can find parasol-like structures that stand upwards of 2.5 centimeters (1 inch) above the thallus. If the structure is segmented and resembles a palm tree, it is growing on a female plant and the structure (a gametophore) will produce female gametes. If it is only slightly segmented, more like the outline of a doily, it is growing on a male plant, and the structure (gametophore) will produce male gametes.
Marchantia is found on moist, usually neutral or basic soils or on wet rock, such as along a perennial stream. It occasionally shows up on mineral soils in depressions or in the shade of fallen logs following hot forest fires. It is cosmopolitan in its distribution, and is probably in every state and province. In many locations is considered a weed. It is often associated with human activity.
This is the only native genus of thalloid liverworts that produces gemmae cups.