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Strawberry pine, J. Hooker  1845

Microcachrys - Strawberry pine description


Evergreen shrubs without any upright main trunks. Bark fibrous, flaking in scales and then peeling in long strips and becoming shallowly furrowed with age. Juvenile and adult foliage similar. Branchlets weakly differentiated into long shoots of main axes and primarily photosynthetic short shoots, hairless, completely hidden by the leaves until thickening growth brings them into view. Resting buds not well developed, consisting solely of young, unexpanded foliage leaves. Leaves attached in pairs, each pair at right angles to the preceding one, scalelike, overlapping, closely hugging the twigs, edged by a thin, toothed, papery fringe.

Plants dioecious. Pollen cones single at the tips of otherwise ordinary foliage shoots, egg-shaped to cylindrical. Each pollen cone, with a few bracts at the base and with (12-)16-24(-28) seemingly spirally arranged (by crowding of alternating whorls of 4) pollen scales. Each scale roundly and broadly triangular, with two pollen sacs. Pollen grains small (body 25-40 µm long, 30-45 µm overall), with (two or) three (to six) round, nearly smooth air bladders, extending a little beyond and partially tucked under the conspicuously larger, almost featurelessly smooth, squashed-ball-shaped body. Seed cones single at the tips of short, otherwise ordinarily foliage branchlets that may alternate in close proximity to one another along a slightly older shoot, somewhat fleshy but recognizably conelike in appearance. Cones with (12-)16-24(-28) seemingly spirally arranged (by crowding of alternating whorls of four) juicy fertile bracts, which do not unite into a podocarpium. Each fertile bract bears one seed near its tip that is pointed back down into the cone axis and is nestled in an asymmetrical, cup-shaped, fleshy seed scale (epimatium). Seed without an extra aril, hard, ending in a tiny, dimpled beak, maturing in two seasons. Cotyledons two, each with two veins. Chromosome base number x = 15.

Wood moderately dense and hard, slightly fragrant, waxy, the off-white sapwood weakly contrasting with the pale brown heartwood. Grain very fine and even, with well-defined, narrow growth rings marked by a gradual transition to a very narrow band of slightly darker latewood. Resin canals absent but sometimes with scattered individual resin cells.

Without stomates on the outer face but with densely packed parallel lines of stomates on the inner face except over the midvein. Each stomate sunken below the level of but visible between the four (to six) surrounding subsidiary cells, which are topped by a prominent, continuous, sharply raised Florin ring. Midvein single, slightly grooved above, not evident beneath, with one large resin canal immediately below it flanked by small wedges of transfusion tissue. Photosynthetic tissue with a palisade layer on the lower (outer) side adjacent to a layer of hypodermis just inside the epidermis.

One species in Tasmania, Australia. Although with its dense, dark green foliage and bright red seed cones, potentially a handsome subject for rock gardens and as a substitute for creeping junipers in moderate climates, strawberry pine (Microcachrys tetragona) is little cultivated, and there has been no cultivar selection. The genus name, Greek for “little catkin”, refers to the pollen and seed cones, small in comparison to those of the unrelated Tasmanian cedars of the genus Athrotaxis (Cupressaceae), in which strawberry pine was placed when in was first described. Based on both morphological features and DNA studies, Microcachrys is clearly related to Microstrobos, another Australian genus, but the relationships of these two genera to other podocarps are less clear. In phylogenetic trees of the family, they branch near the base of the group of genera including both Dacrydium and Podocarpus. Sharing this near basal position with them are. Saxegothaea of Chile and Acmopyle of New Caledonia and Fiji, two genera with little superficial resemblance to Microcachrys and Microstrobos. The relative positions of these three phylogenetic branches (considering Microcachrys and Microstrobos as a single branch) in DNA studies vary with the exact genes sampled. Because the arrangement of branches near the base of a phylogenetic tree is important in assessing the pattern of evolution of characters (like scale leaves versus needle leaves), further study of this aspect of podocarp relationships is warranted.

Unfortunately, the fossil record of Microcachrys shoots, which might shed some light on character evolution, is very sparse. Outside of relatively recent specimens from Tasmanian ice-age deposits, less than 2 million years old, there is just a single shoot from Miocene coals (10-20 million years old) near Melbourne, Victoria, Australia. Sparse as they may be, these fossils are nonetheless interesting because some come from lowland vegetation while the sole living species, strawberry pine (Microcachrys tetragona), presently inhabits the subalpine zone. In contrast to this meager macrofossil record, pollen with mostly three air bladders closely resembling the distinctive pollen of the living strawberry pine is known from sediments as old as the Jurassic, more than 150 million years old, and from localities all across southern Australia, in New Zealand, Kerguelen, and possibly in India, disappearing from New Zealand and most of mainland Australia after the Oligocene, some 23 million years ago. This extended fossil record is in keeping with the relatively basal position of strawberry pine in phylogenies of the Podocarpaceae, implying that its ancestors diverged from other podocarps fairly early in the history of the family.




Attribution from: Conifers Garden