Corail (Schmid 1981).
The sole species in Parasitaxus de Laub. 1972. Syn: Dacrydium ustum Vieillard 1861; Podocarpus ustus (Vieill.) Brogn. et Gris 1866; Nageia usta (Vieill.) Kuntze 1891 (Farjon 1998). Studies of cuticle micromorphology suggest a close relationship with Lepidothamnus, particularly with L. fonkii (Stockey et al. 1995). See also Sinclair et al. (2002), abstract, shown below.
A shrub or small tree, 1.0-1.8 m tall (de Laubenfels 1972).
New Caledonia: Pouebo, Bleue River, type from Poila, found at 400-1100 m elevation (Silba 1986). Based on data from 19 collection localities, its climate preferences include a mean annual temperature of 20.2°C, with an average minimum in the coldest month of 13.3°C, and a mean annual precipitation of 1938 mm (Biffin et al. 2011, Table S5). Zone 10 (cold hardiness limit between -1°C and +4.4°C) (Bannister and Neuner 2001).
The IUCN reports that this taxon is "vulnerable" to extinction in the wild. Based on results of a 2009 assessment, it has a limited geographic range that is severely fragmented with continuing decline in both the extent/quality of habitat and the number of mature plants, which include no more than 10,000 mature individuals with no more than 1,000 in any subpopulation.
It is a very difficult plant to locate in the wild and, because it can be killed simply by stepping on the delicate shoots that are often concealed beneath forest litter, it is probably best if no one seeks to observe it unless they have a valid scientific reason -- preferably, a reason connected with the preservation and protection of this unique and very rare conifer.
You will often see this species called Parasitaxus ustus. However, the Latin word for yew, taxus, is feminine; thus adjectives such as ustus, meaning "burnt" (a reference to the brownish foliage?), should also be feminine. This principle applies equally to names in the other genera derived from taxus: Amentotaxus, Austrotaxus, Cephalotaxus, Pseudotaxus, and Taxus.
This is the only known 'parasitic' gymnosperm. Its parasitism operates through a vesicular-arbuscular mycorrhiza, and the plant appears to be connected to its host through a root graft (Woltz et al. 1994). As such it is a singular parasitic relationship. Formerly this mode of parasitism was a great mystery, but recent studies (Feild and Brodribb 2005) have revealed much about its physiology, which differs from any of the more than 3,000 described angiosperm parasites. The foliage and shoots have chloroplasts, but lack any significant photosynthetic electron transport. The transfer of carbon (sugars) from the host plant is achieved mainly through a fungal intermediary, as in the case of mycoheterotrophs such as the nonphotosynthetic ericads pinesap (Hypopitys) and indian-pipe (Monotropa), but a direct xylem connection with the host may also occur and may facilitate nitrogen tranfer from the host. The plant also has a high stomatal conductance and low water potential, like the mistletoes. Thus it has a unique form of parasitism unlike any other known plant. Apropos, the nitrogen-scavenging ability of Parasitaxus also allows it to produce cone crops the year around, even in plants as small as 15 cm tall, despite growing in extremely poor ultramafic soils (Feild and Boddribb 2005).
More general remarks of interest were put forth by de Laubenfels (1959) when he first investigated the species:
"[Parasitaxus ustus] has always occupied a unique position ... among conifers in general. It grows in remote, densely forested highland parts of New Caledonia. ... Its uniqueness has derived from the fleshy deep red or purple scale-leaved branches ....
"Because of the special interest which P. ustus has aroused, a special effort was made during a December 1957 visit to New Caledonia to collect the elusive plant. One of its areas of occurence was visited, and several plants were seen. This report derives from the fact that one of these plants was growing out of the base of a tree of [Falcatifolium taxoides]. As might be suspected from the fleshy red nature of P. ustus, it is a parasite, certainly sometimes, probably always. The parasitic specimen was collected and has been the subject of a careful study.
"[Parasitaxus ustus] is a woody shrub. In the case of its attachment to [F. taxoides], the largest of two emerging stems had a diameter of about [12 mm] and the host had a diameter of about [8 cm]. The parasitic stem curves sharply so that the root zone is oriented upward. Most of the woody roots travel up the trunk of the host, probably for several feet; a few grow downward for several inches. The modified roots are imbedded in the bark between the cork cambium and the vascular cambium. General stimulation of the vascular cambium has occurred, producing a thickening in both wood and bark tissue. The cambium of the slightly anastomosing roots, significantly, is on the outside toward the cork cambium. No normal phloem is produced, although a tissue full of sclerids opposite the xylem may represent modified phloem tissue. Around the parasitic roots, the host tissue is somewhat disorganized and forms a sheath of abnormally large cells.
"In several ways the specimen of P. ustus reported here is not typical. No other specimen has been seen growing from the trunk of another plant. Typically P. ustus grows on the open forest floor under rather shady conditions (chlorophyll is present in the leaves). Probably most individuals are root parasites. Several attempts by foresters in New Caledonia to dig up small specimens for transplanting resulted in immediate death of the specimens. It was noticed that removing the specimens involved cutting out various tree roots, but, because a parasitic attachment was not expected, it was not looked for. ...
"Until now, all conifers were known to be independent trees, bushes, or trailing shrubs. Podocarpus ustus, in being parasitic, thus differs from all other conifers. In fact no gymnosperm of any kind has previously [or since] been discovered in a parasitic relationship to other plants." (de Laubenfels 1959).
de Laubenfels, David J. 1959.07.10. Parasitic conifer found in New Caledonia. Science 130:97.
Feild, T.S. and T.J. Boddribb. 2005. A unique mode of parasitism in the conifer coral tree Parasitaxus ustus (Podocarpaceae). Plant, Cell and Environment 28: 1316-1325. Abstract: Almost all parasitic plants, including more than 3000 species, are angiosperms. The only suggested gymnosperm exception is the New Caledonian conifer, Parasitaxus ustus, which forms a bizarre graft-like attachment to the roots of another conifer Falcatifolium taxoides. Yet, the degree of resource dependence of Parasitaxus on Falcatifolium has remained speculative. Here we show that Parasitaxus is definitively parasitic, but it displays a physiological habit unlike any known angiosperm parasite. Despite possessing chloroplasts, it was found that the burgundy red shoots of Parasitaxus lack significant photosynthetic electron transport. However unlike nonphotosynthetic angiosperm parasites (holoparasites), tissues of Parasitaxus are considerably enriched in 13carbon relative to its host. In line with anatomical observations of fungal hyphae embedded in the parasite/host union, stable carbon isotopic measurements indicate that carbon transport from the host to Parasitaxus most likely involves a fungal partner. Therefore, Parasitaxus parallels fungus-feeding angiosperms (mycoheterotrophs) that steal carbon from soil mycorrhizal fungi. Yet with its tree-like habit, association with fungi residing within the host union, high stomatal conductance, and low water potential, it is demonstrated that Parasitaxus functions unlike any known angiosperm mycoheterotroph or holoparasite. Parasitaxus appears to present a unique physiological chimera of mistletoe-like water relations and fungal-mediated carbon trafficking from the host.
Sinclair, W. T., R. R. Mill, M. F. Gardner, P. Woltz, T. Jaffre, J. Preston, M. L. Hollingsworth, A. Ponge, and M. Moller. 2002. Evolutionary relationships of the New Caledonian heterotrophic conifer, Parasitaxus usta (Podocarpaceae), inferred from chloroplast trnL-F intron/spacer and nuclear rDNA ITS2 sequences. Plant Systematics and Evolution 233:79-104. Abstract: The phylogenetic position of Parasitaxus (Podocarpaceae) has been inferred from a cladistic analysis of molecular characters from chloroplast and nuclear genomes including all genera of Podocarpaceae. In all 24 most parsimonious trees, based on combined datasets, Phyllocladus resided outside Podocarpaceae s. str. while Lepidothamnus was basal to the latter. Most other genera were arranged in two major clades. The evidence confirms previous studies, which have suggested a relationship between Lagarostrobos, Manoao and Parasitaxus. Parasitaxus is not directly related to its host Falcatifolium taxoides. Instead it appears to be most closely related to Manoao and Lagarostrobos. No other members of this group now occur on New Caledonia. However, if the evolution of Parasitaxus were autochthonous, a free-living member of this group must once have occurred there. An accelerated evolutionary rate of the chloroplast sequence analysed was suggested, indicating that the plant behaves like a holoparasite.
Stockey, Ruth A., Helen Ko and Philippe Woltz. 1995. Cuticle micromorphology of Parasitaxus de Laubenfels. International Journal of Plant Sciences 156: 723-730. Abstract: Cuticle micromorphology of three collections of the parasitic conifer Parasitaxus ustus (Vieillard) de Laubenfels (Podocarpaceae) was studied with scanning electron microscopy. External and internal cuticle features of abaxial and adaxial leaf surfaces of both vegetative and epimatium-bearing branches are characterized. Leaves are amphistomatic with an abaxial tip lacking stomata and a small marginal frill. Cuticle is thin and external surfaces exhibit sunken Florin rings and highly undulating epidermal cell surfaces. Stomata have a scattered orientation on the leaf and have three to six subsidiary cells. Cuticle on the subsidiary cells, guard cells, and epidermal cells is smooth to slightly granular. Stomata lack polar extensions. Epidermal cells have variable shapes but are more elongate and rectangular near the abaxial leaf tip and between stomatal groups. Micromorphological characters are compared to those of the host plant, Falcatifolium taxoides (Brongniart et Gris.) de Laubenfels, and Florin's Dacrydium group C species that are considered by some workers to represent three separate genera: Halocarpus Quinn, Lepidothamnus Philippi, and Lagarostrobos Quinn. Micromorphologically cuticles are most similar to those of the genus Lepidothamnus, in particular L. fonkii Philippi, but those of Parasitaxus have less granular epidermal cell surfaces and a more irregular outline to the stomatal apparatus.
Woltz, P.R., A. Stockey, M. Gondran and J. F. Cherrier. 1994. Interspecific parasitism in the gymnosperms: unpublished data on two endemic New Caledonian Podocarpaceae using scanning electron microscopy. Acta Bot. Gallica 141: 731-746.
Association Endemia, a site devoted to New Caledonian species. Has excellent photos, a range map, and other information. In French.
The species account at Threatened Conifers of the World.
Köpke, E., L. J. Musselman, and D. J. de Laubenfels. 1981. Studies on the anatomy of Parasitaxus ustus and its root connections. Phytomorophology 31: 85-92.
Nickrent, D. 2006.10.11. Is Parasitaxus parasitic? http://www.parasiticplants.siu.edu/parasitaxus.html, accessed 2009.11.04.
Last Modified 2017-12-29