by Piter Kehoma Boll
Liveworts often live in moist and shady spaces and, even if we know how to identify them as liverworts, they often look all the same. However, if we pay attention to the details, differences can often be perceived.
Pellia epiphylla, commonly known as the common pellia, is a liverwort that loves very humid places, so it often grows very close to rivers and other watercourses in North America, Europe, North Africa and some nearby areas in Asia. Its thalli are smooth and slightly fleshy, about 1 cm wide and can reach several cm in length. They like ro remain in a horizontal position, so they grow very attached to the horizontal subtrates but tend to grow away in vertical ones, acquiring a more ruffled aspect. Although usually completely green, the thalli can have a purplish or reddish tinge along the middle, especially when they grow too far from water, which can help identify this species. Otherwise it is very featureless compare to many other liverworts.
As with all liverworts, the thallus of the common pellia is the gametophyte, i.e., the haploid generation (with only one chromosome of each type per nucleus) and that generates the gametes. Although in many liverworts the gametophytes are either male or female, they are monoicous (i.e, hermaphrodites) in the common pelia. The male sex organs (antheridia) occur along the middle, appearing as very small light and shiny dots, while the female ones (archegonia) occur close to the tip and remain covered. Fertilization, as usually, occurs when the plant becomes wet. The antheridia absorb water to the point that they burst, releasing the sperm cells (antherozoids) that swim to the archegonia, where fertilization occurs.
The resulting zygote gives rise to the sporophyte, a diploid generation (with two chromosomes of each type per nucleus) and it grows from inside the archegonia in the form of a very long and slender whitish stalk with a dark capsule at the tip. When the capsule is mature, it bursts and releases the spores, which will germinate and originate new gametophytes. The group of sporophytes growing from the gametophyte give the set a peculiar “hairy” aspect, which also helps recognize this species.
Being a common species across its range, the common pellia has been studied to understand physiological and reproductive characteristics of liverworts, as well as some ecological aspects. For example, it is known that, while the gametophyte absorbs water mostly through the under surface, the antheridia absorb it from the upper surface, and the lower midrib of the plant compared to the border is essential to retain water for this. While the sporophyte of many liverworts is completely dependent on its mother, the gametophyte, to receive water, that of the common pellia is much more indepenent, absorbing most of it from the environment.
Although fairly featureless, the common pellia still has its charm.
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References:
Clee A (1939) The Morphology and Anatomy of Pellia epiphylla considered in Relation to the Mechanism of Absorption and Conduction of Water. Annals of Botany 3(1): 105–111. https://doi.org/10.1093/oxfordjournals.aob.a085045
Greenwoo HE (1911) Some Stages in the Development of Pellia epiphylla. The Bryologist 14(4): 59-70. https://doi.org/10.2307/3238074
Wikipedia. Pellia epiphylla. Available at <https://en.wikipedia.org/wiki/Pellia_epiphylla >. Access on 27 August 2020.
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