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Plum-seeded yew, R. Philippi 1860

Prumnopitys - Plum-seeded yew description


Evergreen trees of varying habit. Trunk cylindrical to irregular, columnar and limbless to a great height or breaking up into branches near the base. Bark obscurely fibrous, thin, scaly, shedding continuously in irregular patches ranging in size from flakes to small plates to produce a mottled appearance, sometimes becoming shallowly furrowed into narrow, vertical strips with age. Crown dense, spherical, egg-shaped, or cylindrical, compact to spreading, becoming irregular with age, with numerous slender, upwardly angled branches, often rapidly subdividing toward the periphery. Branchlets all elongate, without distinction into short and long shoots, hairless, remaining green for at least the first year, obscurely to prominently grooved between the elongate, attached leaf bases. Resting buds small, well developed, generally spherical and surrounded by specialized, green bud scales. Leaves spirally attached but often presented primarily in two flat rows by bending of the petioles, usually needlelike (broadly sword-shaped in Prumnopitys amara) and strongly resembling those of yews (Taxus), straight or slightly to moderately sickle-shaped, flattened top to bottom.

Plants dioecious (or rarely some individuals monoecious). Pollen cones single at the tip of or in a leaf axil on an ordinary foliage shoot or, more commonly, spirally arranged in groups of up to about 40 in the axils or more or less reduced leaflike bracts on specialized axillary reproductive shoots. Each pollen cone cylindrical, usually without a ring of bracts at the base and with numerous, spirally arranged, roundly triangular pollen scales, each bearing two pollen sacs. Pollen grains medium to very large (body 25-70 µm long, 45-115 µm overall), with two round, coarsely wrinkled air bladders distinctly smaller than the minutely bumpy body or rarely uniting to form a single bladder completely encircling the body around the equator. Seed cones generally single on a specialized axillary reproductive shoot clothed with scale leaves or variously reduced foliage leaves. Individual cones highly modified, rather open, with 1-12 widely spaced, spirally arranged fertile bracts, neither these nor the axis becoming fleshy (there in no podocarpium), each bract with a single seed completely embedded in the fleshy seed scale (the epimatium), the opening of the ovule pointing down into the cone axis. Combined seed coat and epimatium with a crest culminating in a pointed, single or double beak and with a thick, hard, fruit-stone-like layer inside the juicy, fleshy layer (hence the scientific name, Greek for “plum pine”). Seeds maturing and falling in one or two seasons. Cotyledons two (or three), each with two veins. Chromosome base numbers x = 18 and 19.

Wood relatively hard heavy, sometimes with an unpleasant odor, the white to light brown sapwood sharply contrasting with the yellow to reddish brown to dark brown heartwood, which often has red or black streaks. Grain fine and even, usually with evident growth rings marked by narrow bands of darker latewood. Resin canals absent but often with scattered or clumped individual resin parenchyma cells.

Leaf surface with or without accompanying scattered stomates above and with several discontinuous lines of stomates forming a broad, pale, stomatal band on either side of the midrib beneath. Each stomate filled with a plug of wax and sunken deeply beneath and mostly hidden by the four (to six) surrounding subsidiary cells, which have a very thick cuticle topped by a low Florin ring surrounded by a sunken channel. Midvein single, prominent, weakly raised beneath and raised to grooved above, with one (to three) small resin canals immediately beneath it, small bands of transfusion tissue on either side (extending out to the edge of the leaf in Prumnopitys amara), and occasionally with scattered clumps of accessory transfusion tissue extending all the way out to the leaf edge. Photosynthetic tissue forming a well-developed palisade layer unaccompanied by a hypodermal layer beneath the upper epidermis and connecting extensively to the spongy mesophyll or separated by the accessory transfusion tissue.

Ten species in the western Pacific from Sumatra (Indonesis) and Luzon (Philippines) to New Zealand and in the New World cordilleran region from Costa Rica and Venezuela to Chile and Argentina.

Only a few species of Prumnopitys are occasionally cultivated outside their homelands, including Prumnopitys andina and Prumnopitys taxifolia. Even within their native regions, they are rather infrequent, and no cultivar selection has taken place. With their handsome, dark green crowns, interesting bark, and conspicuous pollen cones or colorful juicy seed cones, they are worthy of greater attention in the tropics and subtropics.

Several DNA studies show that these are two major groupings of podocarp genera, one containing Podocarpus and Dacrydium and related genera, embracing the majority of species in the family, while the other contains a smaller, less clearly defined grouping of genera, most of which have scaly leaves. Of the six currently recognized podocarp genera formerly included as botanical sections with Podocarpus, four are at least moderately closely related to this large genus and belong in the same grouping while the other two are not at all related to it and belong with the other group of genera. Parasitaxus, formerly treated as Podocarpus sect. Microcarpus, closely resembles the scaly-leaved genera, especially Manoao and Lagarostrobos, and so occasions little surprise in the reassessment of its taxonomic position. However, Prumnopitys superficially resembles several genera in the Podocarpus group, so much so that some authors were reluctant to accept its separation from Podocarpus despite well-known differences in biochemistry (such as flavonoid pigments) and morphology (such as complete lack of a podocarpium). An alliance with the scaly-leaved genera was never suspected before DNA studies revealed it.

DNA studies also show fairly decisively that broadleaf miro (Prumnopitys amara) id firmly embedded among the other Prumnopitys species and should not be set off from them in a separate botanical section or even a separate genus. This separate section or genus, named sundacarpus, was proposed and then fairly widely accepted largely because broadleaf miro has much larger, more Podocarpus-like leaves than the other species, all of which have rather yewlike foliage. The seed cones and pollen cones of broadleaf miro are very similar to those of the other species of Prumnopitys, with DNA studies showing that the unusual leaves of Prumnopitys amara arose within the genus rather than reflecting significant separation. However, even though the unity of Prumnopitys and its relationship to the scaly-leaved genera now seem well established, the relationships among the species within the genus is a completely open question and worthy of detailed study.

There is a modest fossil record of Prumnopitys known from the Australian region but not from South America. The oldest known fossils are found in Paleocene sediments (about 60 million years old) of New Zealand, where the genus still occurs. The only other Tertiary occurrences of Prumnopitys from New Zealand date from about 20 million years ago, in the Miocene, and these are considered so similar to one of the two extant species in New Zealand, matai (Prumnopitys taxifolia), that they are assigned to that species. All other known fossils of Prumnopitys are found in southern Australia (Tasmania and Victoria), outside the present range of the genus, and date to the Eocene, roughly 50 million years ago. Like so many other podocarp fossils from the early Tertiary of southern Australia, these fossil leaves have numerous stomates on both leaf surfaces, indicating a much wetter climate in Australia’s past than it presently experiences.




Attribution from: Conifers Garden