Parasitaxus
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''Parasitaxus usta'', also known in French as ''cèdre rabougri'', is a rare
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of
conifer Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...
of the
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Podocarpaceae Podocarpaceae is a large family of mainly southern hemisphere conifers, known in English as podocarps, comprising about 156 species of evergreen trees and shrubs.James E. Eckenwalder. 2009. ''Conifers of the World''. Portland, Oregon: Timber Pres ...
, and the sole species of the
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
''Parasitaxus''.


Description

It is a woody
shrub A shrub or bush is a small to medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees by their multiple ...
up to 1.8 m
endemic Endemism is the state of a species being found only 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 foun ...
to the remote, densely forested areas of
New Caledonia New Caledonia ( ; ) is a group of islands in the southwest Pacific Ocean, southwest of Vanuatu and east of Australia. Located from Metropolitan France, it forms a Overseas France#Sui generis collectivity, ''sui generis'' collectivity of t ...
, 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 New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
) and '' Lagarostrobos'' (
Tasmania Tasmania (; palawa kani: ''Lutruwita'') is an island States and territories of Australia, state of Australia. It is located to the south of the Mainland Australia, Australian mainland, and is separated from it by the Bass Strait. The sta ...
). ''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.) 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 gymnosperms ( ; ) are a group of woody, perennial Seed plant, seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include Pinophyta, conifers, cycads, Ginkgo, and gnetoph ...
. The species lacks
root In vascular plants, the roots are the plant organ, organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often bel ...
s 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 haustorial parasite, which is usually the case with
angiosperm Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed within a fruit ...
s. Certain experts therefore consider the plant as a myco-heterotroph.


References


Gymnosperm Database: ''Parasitaxus usta''
* Nickrent, D. (2006)
Parasitic Plants website: Is ''Parasitaxus '' Parasitic?
{{Taxonbar, from=Q13077228, from2=Q133097 Endemic flora of New Caledonia Monotypic conifer genera Podocarpaceae genera Podocarpaceae