''Isoetes taiwanensis'' is a species of

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...

in the family

Isoetaceae Isoetaceae is a family including living quillworts (''Isoetes'') and comparable extinct herbaceous lycopsids (''Tomiostrobus ''Tomiostrobus'' is an extinct quillwort genus from the Early Triassic of Australia, China and Russia, which was espe ...

. It is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...

, and the only species of

quillwort ''Isoetes'', commonly known as the quillworts, is the only extant genus of plants in the family Isoetaceae, which is in the class of lycopods. There are currently 192 recognized species, with a cosmopolitan distribution but with the individual s ...

there. As other quillworts, it is relatively small, with erect leaves long. It grows submersed in shallow ponds for most of the year.

IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

considers it critically endangered because of habitat loss. The first quillwort genome sequence was of ''I. taiwanensis''. This showed that there were differences in its biochemistry from terrestrial plants that had adopted the same strategy for CO₂ fixation, namely

Crassulacean acid metabolism Crassulacean acid metabolism, also known as CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions that allows a plant to photosynthesize during the day, but only exchange gases at night. ...

(CAM). This involves the enzyme

phosphoenolpyruvate carboxylase Phosphoenolpyruvate carboxylase (also known as PEP carboxylase, PEPCase, or PEPC; , PDB ID: 3ZGE) is an enzyme in the family of carboxy-lyases found in plants and some bacteria that catalyzes the addition of bicarbonate (HCO3−) to phosphoenolp ...

(PEPC) and plants have two forms of the enzyme. One is normally involved in CO₂ fixation during photosynthesis and the other in central metabolism. From the genome sequence, it appears that in ''I. taiwanensis'' both forms are involved in photosynthesis. In addition, the time of day of the peak abundance of some of the components of CAM was different from terrestrial plants. These fundamental differences in biochemistry suggests that CAM in ''I. taiwanensis'', and likely all quillworts, is another example of

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...

of CAM.

References

taiwanensis Endemic flora of Taiwan Critically endangered plants Taxonomy articles created by Polbot Plants described in 1972 {{Lycophyte-stub