Spore production in two common Bryophytes

Brian King

Bryophytes are a transitional group between the green algae, and the vascular plants. In this group are the hornworts, liverworts and true mosses.

Some features that distinguish them from the charophycean green algae are:

- presence of male and female reproductive structures (antheridium and archegonium)

- retention of the zygote and developing embryo within the archegonium on the female sporophyte

- multicellular diploid sporophyte, producing many spores

While many do have water conducting tissues, these are not lignified, and are thus not xylem and phloem.

The phylum Hepatophyta contains the plants know as liverworts. There are approximately 6000 species in the group. Like most bryophytes, they live in moist, shaded areas. The haploid (gametophyte) stage in the lifecycle is dominant, and usually arise directly from spores, although asexual reproduction via “gemmae cups” also occurs.

After fertilization of the haploid egg within the archegonium by the flagellated sperm, the diploid zygote then undergoes mitosis to form a multicellular, diploid sporophyte. The sporagenous tissue then undergoes meiosis to form spores, which are then dispersed, and germinate to form the dominant gametophyte phase of the life cycle.

This is a section through the mature sporphyte of Marchantia, a common thalloid (flat) liverwort. Photo was taken at 40x.

The seta is the short stalk suspending the sporangium. The foot is the anchor of the sporphyte to the mother gametophyte. The calyptra is haploid gametophyte tissue that is torn away, as the gametohyte enlarges. The sporangium is the diploid sporophyte tissue that gives rise to the haploid spores.

Mosses are in the phylum Bryophyta. There are three classes – Sphagnidae (peat mosses), Andreaedae (granite mosses), and Bryidae (true mosses). The true mosses are the largest group, with more than 9500 species, with new species being discovered regularly. The reproduction of mosses is similar to the other Bryophytes, such as liverworts. There are male and female gametangia, and a maternally nourished sporophyte. The gametophyte stage is the dominant phase of the life cycle.

This is a picture of the capsule of a mature sporophyte from Mnium, a common moss. Two photos were taken at 40x each.

The diploid sporagenous tissue gives rise to the haploid spores. These spores are released via the peristome, an opening at the end of the capsule. This hole is guarded by teeth that curl back when conditions are favorable for dispersal. The operculum is a cap covering the peristome. The seta is quite long, and is connected to the gametophyte by a foot.

Work Cited:

Raven, Peter H., Evert, Ray F., Eichhorn, Susan E. 1999. Biology of Plants, Sixth Edition. W.H. Freeman and Company, Worth Publishers. New York