Division Hepatophyta: The Liverworts

Individual liverwort plants, like mosses, are very small. However, a colony of liverworts may cover vast spaces in suitable environments. Also, like the mosses, the gametophyte generation of the liverwort is dominant. The green body of the liverwort is called a thallus.  

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Figure 7. This photograph shows colonies of green liverwort gametophytes called thalli, the body or leaf-like larger base structures. The gemmae cups (resembling tiny thin cups) growing from the thalli contain clusters of haploid cells.
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Liverwort thalli may contain cup-shaped structures called gemmae cups. The gemmae cups contain small masses of haploid cells called gemmae. When a raindrop hits a cup, the gemmae are splashed out. Each of the gemmae may develop into a clone of the parent plant if it lands in favorable conditions.

Liverworts also exhibit alternation of generations. The gametophyte plants produce either antheridiophores or archegoniophores. Both structures are elevated from the thallus by a stalk-like structure. The head of the antheridiophore is disk-shaped, and it contains the antheridia. Each antheridium is capable of producing many flagellated sperm.

 

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Figure 8. This photograph show the antheridiophore of a liverwort. The head of the antheridiophore is disk-shaped appearing brownish in color and grows on a stalk coming from the thallus.
CC BY: V.H. Hammer 

 

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Figure 9. The female gametophytes produce structures called archegoniophores. The archegoniophores have heads shaped like an umbrella's skeleton shown here in green with a lighter center and darker tips.
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The female gametophytes produce structures called archegoniophores. The archegoniophores have heads shaped like an umbrella's skeleton. These heads contain archegonia. Each archegonium may produce an egg.

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Figure 10. A micrograph of a cross section of an archegoniophore with differentiation in parts in blue and pink.
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Figure 11. A micrograph of an archegonium with an egg.
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 Figure 12. Liverwort Life Cycle. The cycle starts with the sperm (shown in red) entering the archegonium (green structure in the top blue box) and fertilizing the egg (orange sphere) forming an embryo (yellow/orange cluster) and developing in to a mature sporophyte. Spores (orange circle in the top blue box) then germinate into flattened thalli (green lobed leaf-like structure) attached to the substrate by thin, single celled filaments called rhizoids. Male (shown on the right) and female (shown on the left) gametophytes develop on separate, individual plants. Once released, male gametes (the red sperm) swim with the aid of their flagella (shown in dark blue) to the female gametophyte (the archegonium shown in the pink box), and fertilization ensues. The zygote grows into a small sporophyte still attached to the parent gametophyte. It will give rise, by meiosis, to the next generation of spores.
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