Austrotaxus
New Caledonia yew, R. Compton 1922
Taxaceae
Austrotaxus - New Caledonia yew description
Evergreen trees or shrubs. Trunk cylindrical or irregular, often branched from near the base. Bark fibrous, smooth at first, flaking in scales or short strips and then becoming shallowly furrowed between flat ridges peeling in strips. Crown dense, cylindrical to dome-shaped, with numerous thick, crooked branches bearing alternate or paired branchlets. Branchlets all elongate, without distinction into long and short shoots, hairless, remaining green for the first year or two, smooth and without apparent attached leaf bases. Resting buds small, distinct but somewhat loosely constructed of hard, triangular bud scales that fall with shoot expansion leaving conspicuous rings of scars. Leaves spirally attached and crowded toward the end of the growth increment. Each leaf needlelike, sword-shaped, straight to moderately sickle-shaped, flattened top to bottom.
Plants dioecious. Pollen cones attached singly in the axils of about 15 spirally arranged bracts along crowded, short reproductive spikes, the spikes in the axils of fallen bud scales ringing the base of new flushes of foliage. Each pollen cone united with its bract, much reduced, consisting of four or five crowded pollen scales with little or no five tip and one or two pollen sacs, the whole individual pollen cone giving the appearance of a single pollen scale with about seven pollen sacs. Pollen grains small (25-30 µm in diameter), nearly spherical, without any apparent germination aperture, minutely but conspicuously warty, otherwise featureless. Seed cones single or two or three around the base of a new flush of foliage, each at the tip of a very short, entirely scaly stalk in the axil of a fallen bud scale. Each seed cone without any trace of seed scales, consisting of a single seed and aril seated in a cup of bracts at the tip of the stalk. Seeds plump, closely covered except at the tip by but not united with the aril, only the aril fleshy. Outer seed coat hard, opening straight opposite and pointing away from the stalk, maturing in a single season and falling with the withering of the aril if the cones are not earlier removed by fruit-eating birds or mammals. Cotyledons two, each with one vein. Chromosome base number unknown.
Wood moderately hard and heavy, light brown. Grain fine and very even, with indistinct growth rings marked by a gradual transition to a few rows of smaller-celled but not darker latewood. Resin canals absent but with a few, scattered individual resin parenchyma cells of the same size as the tracheids (wood cells), which lack spiral thickening.
Without stomates above and with a broad band of stomates on either side of the midrib beneath covering most of the lower surface, each band consisting of many interrupted, and occasionally irregular lines of stomates. Each stomate tucked beneath and largely hidden by the four to six subsidiary cells, which are often shared by adjacent stomates in a line and topped by a steep, incomplete Florin ring. Midvein single, prominent, grooved above and raised beneath, without resin canals, flanked by cylinders of transfusion tissue, and with broad wings of accessory transfusion tissue extending out to the margins. Photosynthetic tissue forming a single palisade layer covering the upper side of the leaves directly beneath the epidermis without an intervening hypodermis.
One species in New Caledonia. Austrotaxus is the only genus of Taxaceae native in the southern hemisphere (hence the scientific name, Latin for “southern yew”). It is most similar to catkin yew (Amentotaxus) in overall appearance but is actually more closely related to yew (Taxus) and white-cup yew (Pseudotaxus). It belongs with the latter genera in one of three lineages in the family, while catkin yew belongs in another one. All three genera in this group lack resin canals in the leaves, a very unusual feature in conifers, but Austrotaxus differs from the other two genera in many features, including its larger leaves and seeds, with a thinner, tight-fitting aril, and its spiky pollen cones. While it seems to share these spikes with Amentotaxus, they are also structurally rather similar to the more condensed compound pollen cones of Pseudotaxus. Alone among genera of Taxaceae, Austrotaxus lacks spiral thickenings in the walls of its wood cells (tracheids). Austrotaxus spicata is not in general cultivation, although it might be in a very few botanical gardens, and there has been no cultivar selection. There is no known fossil record for the genus, although if there were pollen grains in the published record, they would be very difficult to distinguish from those of other genera.
References
- Farjon, A. (2010). A Handbook of the World's Conifers. Koninklijke Brill, Leiden.
- Eckenwalder, J.E. (2009) Conifers of the World: The Complete Reference. Timber Press, Portland.
- IUCN Red List of Threatened Species, International Union for Conservation of Nature and Natural Resources. Cambridge, UK /Gland, Switzerland
Copyright © Aljos Farjon, James E. Eckenwalder, IUCN, Conifers Garden. All rights reserved.