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Glyptostrobus

Chinese swamp cypress, Endlicher 1847
Cupressaceae

 

Irregularly deciduous trees with a single, straight trunk, clothed with thin, fibrous bark peeling in vertical strips. Crown conical to dome-shaped, to open, intermittently branched from the base of the trunk with upwardly angled branches. Shoot system differentiated into annually deciduous short shoots and persistent long shoots, these remaining green 2-3 years. Leaves spirally arranged, those of seedlings and young trees flat, linear, and needlelike, radiating on long shoots and flattened into two rows on short shoots. Those of adult trees of two intergrading types: scalelike and densely overlapping on long shoots and reproductive shoots, clawlike and twisted into two rows on short shoots.

Plants monoecious. Pollen cones in small groups, each single at the end of a short, sparsely branched reproductive branch near the young seed cones, spherical, with 15-20 spirally arranged pollen scales, of which the lower three or four are sterile. Fertile pollen scales with a thin stalk, leaflike blade, and 5-7(-10) spherical pollen sacs at their junction. Pollen grains small (25-40 µm diameter), spherical, with a short, curved germination papilla, but otherwise almost featureless. Seed cones single at the ends of short reproductive branchlets more or less pear-shaped, woody, maturing in a single season and remaining intact as their scales spread to release the seeds. Cone scales 20-22(-40), overlapping, spirally arranged, elongate, spoon-shaped (with just the middle four to six scales fully fertile). Each scale with the fertile and bract portions intimately fused, the bract smaller and represented by a triangular protrusion on the external face, the fertile portion ending in about five to eight laterally fused teeth (hence the scientific name, Greek for “carved cone”) and bearing two seeds in notches on the inner face. Seeds oval, with a single wing derived from the seed coat extending downward from one side at the end of the seed body. Cotyledons (four or) five, each with one vein. Chromosome base number x = 11.

Wood moderately light and soft, very decay resistant, with pale whitish sapwood sharply contrasting with reddish brown heartwood. Grain very even and moderately fine, with clearly evident growth rings marked by a somewhat gradual transition to a variable but often narrow band of much smaller, thicker-walled latewood tracheids. Resin canals absent but with numerous individual resin cells scattered through the growth increment.

Stomates arranged in broad bands on either side of the midrib both above and beneath. Each stomate sunken beneath (but not hidden by) the narrow inner circle of four to six subsidiary cells, which have a smooth surface, without a Florin ring. Leaf cross section commonly somewhat diamond-shaped with a single stranded midvein above a single large resin canal and flanked by wedges of transfusion tissue and sometimes with an extra, smaller resin canal out near the leaf edge on each side. Photosynthetic tissue relatively homogeneous inside the epidermis and adjacent (primarily at leaf edges), thin hypodermis, without a well-defined palisade layer, so wholly composed of loosely packed spongy mesophyll without any particular orientation.

One species in southern China. Glyptostrobus is generally considered most closely related to Taxodium but also shows many similarities to Cryptomeria, and one could postulate a common ancestor of the three that most resembled the latter genus, with Taxodium arising last from a Glyptostrobus-like ancestor through increasing specialization for swamp life. Like its relatives, it used to be assigned to the family Taxodiaceae, but there is ample reason to merge these genera into a larger family Cupressaceae. Glyptostrobus pensilis is scarcely frost tolerant and is not particularly handsome, so it is rarely cultivated outside of botanical gardens and there has been no cultivar selection.

The earliest known fossils definitely assignable to Glyptostrobus based on the characteristic seed cones are found in Paleocene sediments of coastal Alaska and the Rocky Mountain Fort Union Group, dating to some 60 million years ago. Like Taxodium and Metasequoia, with which it often grew in swamp forests, Glyptostrobus was widespread during the Tertiary in Eurasia and North America. While it disappeared from North America after the Miocene, it remained in Europe and Japan into the Pliocene.

 

Species:

 

Attribution from: Conifers Garden


 

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