| Parasitaxus | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Gymnospermae |
| Division: | Pinophyta |
| Class: | Pinopsida |
| Order: | Araucariales |
| Family: | Podocarpaceae |
| Genus: | Parasitaxus de Laub. |
| Species: | P. usta |
| Binomial name | |
| Parasitaxus usta | |
| Synonyms | |
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Parasitaxus usta, also known inFrench ascèdre rabougri, is a rarespecies ofconifer of thefamilyPodocarpaceae, and the sole species of thegenusParasitaxus.
It is a woodyshrub up to 1.8 mendemic to the remote, densely forested areas ofNew Caledonia, first discovered and described byVieillard in 1861. The first definitive report that it was a parasite was in 1959.[2]
Molecular phylogenetic analysis also suggest affinities betweenParasitaxus and the generaManoao (New Zealand) andLagarostrobos (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 thatParasitaxus 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 asDacrydium ustum Vieill.; other synonyms includePodocarpus ustus (Vieill.)Brongn. &Gris, andNageia usta (Vieill.)Kuntze. The name is often cited asParasitaxus ustus, but this is grammatically incorrect, as, according to Latin, the genus nameParasitaxus is (likeTaxus) gender-feminine, with which the species name's gender must agree (Nickrent 2006). The scientific name translates as "parched parasitic yew."
It is generally mentioned thatParasitaxus usta is the only knownparasiticgymnosperm. The species lacksroots and is always found attached to roots identified as ofFalcatifolium taxoides (another member of the Podocarpaceae). The first study of the union ofP. 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 ahaustorial parasite, which is usually the case withangiosperms. Certain experts therefore consider the plant as amyco-heterotroph.[4]
