Parasitaxus usta, also known in French language as cèdre rabougri, is a rare species of conifer of the family Podocarpaceae, and the sole species of the genus Parasitaxus.
Description
It is a woody
shrub up to 1.8 m
Endemism 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.
Taxonomy
Molecular phylogenetic analysis also suggest affinities between
Parasitaxus and the genera
Manoao (
New Zealand) and
Lagarostrobos (
Tasmania).
[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.] Parasitaxus has been shown to contain high levels of chlorophyll.
However, a genome analysis shows that many genes for photosynthesis are missing from the parasite's plastid genome,
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'.
[Gledhill, David (2008). "The Names of Plants". Cambridge University Press. (hardback), (paperback). pp 395] The species was first described as
Dacrydium ustum Vieill.; other synonyms include
Podocarpus ustus (Vieill.) Brongn. & Gris, and
Nageia usta (Vieill.)
Otto 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 plant gymnosperm. The species lacks
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.
However, the question is still left open, as the plant is in any case not a
haustorium parasite, which is usually the case with
. Certain experts therefore consider the plant as a myco-heterotroph.
