A garden liverwort
Ketsanee asked me about a flat green blob growing at Dokmai Garden, so I could as well share with our readers:
An ancient form of life is the liverwort (Division Marchantiophyta or Class Hepaticopsida). The fossil records show that primitive plants and animals occur alone in older sediment layers, while recent sediment layers contain more advanced organisms as well, or instead of older extinct life forms, proving the evolution. DNA analyses of the genomes of today’s living plants and animals help us making pedigrees using a technique not too different from fatherhood analyses. Like our common flowering plants liverworts share a common ancestor among the green algae, and they might in fact have features of the earliest forms of land plants.
The oldest fossil liverworts are more than 400 million years old, 2000 times older than modern Homo sapiens. Geologic dating is based on measuring isotope ratios in crystals in the petrified sediments where the fossils were found. For instance, a brand new zirconia crystal formed during a volcanic eruption contains some Uranium 238 but no Lead 206. Due to radioactive decay of Uranium 238 to the stable Lead 206, the latter accumulates over time. Knowing the constant half-life of a radioactive isotope and the ratio of the two isotopes enables a geologist to make a time approximation of a given sediment.
Mosses, liverworts and algae lack conductive tissues present in ferns and the flowering plants. A moss (Bryophyta) has leaves, but a leafy liverwort lacks the costa or central vein. Some liverworts do not even have leaves and stems, but ‘a flat blob’ called thallus (see picture below). In such cases they usually have an underside different from the topside (a land adaptation), while algae look the same on both sides (both sides are submerged in water). Foliose lichens may have similar shapes, but they are fungi and so composed of a filamentous mycelium with scattered cells of green algae.
Liverworts in Chiang Mai gardens are favoured by high humidity, shade and bare soil. A crust of liverworts may actually keep bare soil together, reducing erosion. In a pot however, they may prevent the water from going deep down into the pot and so you may need to weed them. In larger nurseries manual weeding is not affordable and so chemicals can be used to control liverworts. Liverworts are sometimes used as ornamentals in terraria, aquaria and in moss gardens.
Here is a checklist to Thailand’s 386 species of liverworts and hornworts (pdf from 2008).
Text & Photo: Eric Danell
(Precipitation report: on the 8th of September we received 27 mm of rain, on the 9th we received 15 mm but no rain on the 10th-11th).