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Parasitaxus

Coral pine, (Viellard) de Laubenfels  1972
Podocarpaceae

 

 

Evergreen, red or purple, coral-like, parasitic shrub with numerous relatively short-lived stems emerging from the roots or lower stems of other conifers. Bark thin, smooth or scaly. Crown conical to cylindrical, with a few major branches that are themselves highly and repeatedly branched. Branchlets uniform, not evidently differentiated into long short shoots, all with little elongation between successive leaves. Resting buds poorly defined, consisting of temporarily arrested foliage leaves. Leaves spirally inserted, all scalelike, fairly uniform in size, the base attached for a short distance along the twig, generally hidden by blades of lower leaves, the blades flattened top to bottom, with a keel along the outer (lower) side.

Plants monoecious. Pollen cones single at the ends of branchlets or in the axils of foliage leaves. Each cone oval, without a set of markedly distinct basal bracts, and with just a few spirally arranged pollen scales, each scale bearing two pollen sacs. Pollen grain medium (body 45-50 µm long), with two hemispherical air bladders that are noticeably smaller than the ovoid body and diverge at about 120° away from the germination furrow. Bladders coarsely sculptured within and fairly smooth outside, the cap of the body thicker and more coarsely sculptured than the furrow side. Seed cones single on short, scaly, specialized reproductive shoots at the ends of branchlets or in the axils of foliage leaves, the reproductive part with four to six bracts with long free tips and not swelling to form a podocarpium, maturing in 1 year. Uppermost one (or two) bracts fertile and bearing a single plump, unwinged seed that is completely embedded in and united with the fleshy seed scale (the epimatium). The fleshy layer of the seed coat and epimatium surrounding a hard inner shell of about equal thickness, with the opening of the ovule pointing back down into the cone axis. Cotyledons probably two, each with two veins. Chromosome base number x = 18.

Wood scarcely developed, without heartwood. Stomates in irregular zones on both sides that do not reach the leaf tip. Each stomate sunken beneath the (three or) four or five (or six) surrounding subsidiary cells and surrounded by a Florin ring. Midvein single-stranded, extending only a little way into the blade accompanied beneath by a large resin canal and sometimes with two others off to the sides at the edge of the small wings of transfusion tissue. Functional photosynthetic tissue lacking, the bulk of the leaf occupied by more or less homogenous spongy mesophyll.

One species in New Caledonia. Parasitaxus is the only known parasitic conifer (hence the scientific name, Latin for “parasitic yew”, although it is not related to yews and does not even resemble them). It parasitizes New Caledonian sickle pine (Falcatifolium taxoides), another member of the Podocarpaceae. It produces roots under the bark of the host tree, usually growing on the roots but sometimes emerging out of the bottom of the trunk. The connection between the host and parasite is accompanied by a mycorrhizal fungus that may be involved in the transfer of nutrients between the two plants, as occurs with some hemiparasitic flowering plants. Like many flowering plant parasites, the leaves and branchlets are not green, but those of Parasitaxus do contain chlorophyll, which is not the case with the most extreme flowering plant parasites, like dodders (Cuscuta) in the morning glory family (Convolvulaceae) or Indian pipes (Monotropa uniflora) in the heath family (Ericaceae).

Although Parasitaxus was long treated as a botanical section (section Microcarpus) of Podocarpus, DNA studies suggest that it is more closely related to Manoao (silver pine) and Lagarostrobos (Huon pine), genera once included in Dacrydium and only distantly related to Podocarpus. It lacks the podocarpium found in Podocarpus and its close relatives, and its pollen cones and pollen scales, as well as its exclusively scalelike leaves, also differ greatly from those of Podocarpus to such an extent that it is not obvious why it was ever included in that genus. The anatomy of the stems and the cellular patterns of the epidermis are consistent with a relatively close relationship to Manoao and Lagarostrobos, but the pollen and seed cones are not all that similar. Furthermore, the arrangement of the chromosomes is more similar to that of Podocarpus and its relatives than it is to Dacrydium and the small genera formerly included within it. Clearly, more research is needed, not only on the relationships of Parasitaxus but also on the functioning and origin of its parasitic habit. Such work is not helped by the fact that the sole living species has not proven to be amenable to cultivation, a difficulty shared with some other parasitic plants. Parasitaxus usta is thus not in general cultivation and no cultivar selection has taken place. There is no known fossil record of Parasitaxus that might help in clarifying its relationships.

 

Species:

 

Attribution from: Conifers Garden


 

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