Parasitaxus
Parasitaxus usta, also known in French as cèdre rabougri, is a rare species of conifer of the family Podocarpaceae, and the sole species of the genus Parasitaxus.
| Parasitaxus | |
|---|---|
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Scientific classification  | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Gymnosperms |
| Division: | Pinophyta |
| Class: | Pinopsida |
| Order: | Araucariales |
| Family: | Podocarpaceae |
| Genus: | Parasitaxus de Laub. |
| Species: | P. usta |
| Binomial name | |
| Parasitaxus usta | |
| Synonyms | |
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Description
It is a woody shrub up to 1.8 m endemic to the remote, densely forested areas of New Caledonia, first discovered and described by Vieillard in 1861. The first definitive report that it was a parasite was in 1959.[2]
Taxonomy
Molecular phylogenetic analysis also suggest affinities between Parasitaxus and the genera Manoao (New Zealand) and Lagarostrobos (Tasmania).[3] Parasitaxus has been shown to contain high levels of chlorophyll.[4] However, a genome analysis shows that many genes for photosynthesis are missing from the parasite's plastid genome,[5] strongly suggesting that Parasitaxus completely depends on its host for survival. Around 60% of the genes normally present in a podocarp plastid genome were entirely absent or present only as fragments. They were predominantly genes involved in photosynthetic, rather than other plastid processes. There were changes to the structure of the plastid genome that were different from that of other parasitic plants and its podocarp relatives, although these might not be related to its parasitic lifestyle.
Usta means 'parched'.[6] The species was first described as Dacrydium ustum Vieill.; other synonyms include Podocarpus ustus (Vieill.) Brongn. & Gris, and Nageia usta (Vieill.) Kuntze. The name is often cited as Parasitaxus ustus, but this is grammatically incorrect, as, according to Latin, the genus name Parasitaxus is (like Taxus) gender-feminine, with which the species name's gender must agree (Nickrent 2006). The scientific name translates as "parched parasitic yew."
Ecology
It is generally mentioned that Parasitaxus usta is the only known parasitic gymnosperm. The species lacks roots and is always found attached to roots identified as of Falcatifolium taxoides (another member of the Podocarpaceae). The first study of the union of P. usta with a host showed anatomical changes typical of a parasite.[2] However, the question is still left open, as the plant is in any case not a haustorial parasite, which is usually the case with angiosperms. Certain experts therefore consider the plant as a myco-heterotroph.[4]
References
- Thomas, P. (2010). "Parasitaxus usta". The IUCN Red List of Threatened Species. IUCN. 2010: e.T31002A9597883. doi:10.2305/IUCN.UK.2010-3.RLTS.T31002A9597883.en. Retrieved 12 December 2017.
- Delaubenfels, David J (1959). "Parasitic conifer found in New Caledonia". Science. 130 (3367): 97. doi:10.1126/science.130.3367.97.a.
- Sinclair, W. T., R. R. Mill, M. F. Gardner, P. Woltz, T. Jaffré, J. Preston, M. L. Hollingsworth, A. Ponge, and M. Möller. (2002) Evolutionary Relationships of the New Caledonian Heterotrophic Conifer Parasitaxus Ustus (Podocarpaceae), Inferred from Chloroplast trnL-F Intron/Spacer and Nuclear ITS2 Sequences. Plant Systematics and Evolution 233: 79–104.
- Feild, T.S; Brodribb, T.J. (2005). "A unique mode of parasitism in the conifer coral tree Parasitaxus ustus (Podocarpaceae)". Plant Cell Env. 28 (10): 1316–1325. doi:10.1111/j.1365-3040.2005.01378.x.
- Qu, X-J.; Fan, S-J.; Wicke, S.; Yi, T-S. (2019). "Plastome reduction in the only parasitic gymnosperm Parasitaxus is due to losses of photosynthesis but not housekeeping genes and apparently involves the secondary gain of a large inverted repeat". Genome Biology and Evolution. 11 (10): 2789–2796. doi:10.1093/gbe/evz187. PMC 6786476. PMID 31504501.
- Gledhill, David (2008). "The Names of Plants". Cambridge University Press. ISBN 9780521866453 (hardback), ISBN 9780521685535 (paperback). pp 395