Tsuga diversifolia / northern Japanese hemlock

Tsuga diversifolia, commonly known as northern northern Japanese Hemlock, was described in 1881 by Maxwell Tylden Masters (1833-1907). in Journal of the Linnean Society, Botany, 18th edition. Its Japanese name is コメツガ (kome-tsuga). The epithet is derived from the Latin roots diversis (different, differing, or variable) and folia (leaves), a reference to the length of the needle-like leaves.

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Description. Northern Japanese hemlock is an evergreen coniferous tree that grows to mature heights of 80 feet (25 m) tall, though in high elevations at the northern end of its range, it may adopt a shrubbier habit.

  • The trunk is either straight or forked, measuring up to 3.3 feet (1 m) in diameter, measured at breast height.
  • The furrowed, scaly bark ranges in color from cinnamon brown to gray-brown.
  • The crown is dense, narrow, and conical with youth, becoming rounded and open with age, with spreading branches.
  • Twigs are hairy at first, becoming smooth later on.
  • Winter buds are dark brown, and rounded, measuring 0.08 to 0.12 inches (2 - 3 mm) long.
  • Needle-like leaves are densely arranged in two ranks, with shorter leaves above, ranging from 0.28 to 0.72 inches (7 - 18 mm) long, 0,08 inches (2 mm) wide, with a smooth edge and notched tip. Needle color is glossy green above, and with two white stomatal bands on the underside.
  • Pollen cones are yellow to yellow-orange in color, measuring 0.12 to 0.16 inches (3 - 4 mm) long.
  • Seed cones are numerous on outer branches and are initially green in color, ripening to light (to reddish) brown. They have an ovoid shape, and measure 0.6 to 1 inch (15 - 25 mm) long.

Distribution. This species is endemic to Japan, widespread in northern and central Honshu, with additional populations in Shikoku and Kyushu. It inhabits moist slopes and ridges of mixed montane and subalpine forests at elevations of 2,300 to 8,200 feet (700 - 2,500 m) above sea level. The climate is cool with snowy winters and high summer rainfall, with annual precipitation ranging from 40 to 100 inches (1,000 - 2,500 mm). It is highly frost hardy and wind tolerant.

Of Japan's two native Hemlock species, Tsuga diversifolia occurs at higher elevations. Although their ranges overlap in central Honshu and the southern islands, T. diversifolia and T. sieboldii are not known to hybridize. It regenerates very well and can tolerate rather dense shade, forming pure stands in places. In mixed settings, its coniferous companions include Picea jezoensis, Abies homolepis, A. veitchii, A. mariesii, Larix kaempferi, Pinus parviflora, Thuja standishii, and Thujopsis dolabrata var. hondae. Broad-leaved companions include the genera Rhododendron, Betula, Sorbus, and Quercus. Northern Japanese Hemlock is abundant and widespread in Honshu, has a stable population, including significant tracts in protected national parks, and is not considered threatened. It is managed in Japan as a timber resource, being used for construction, carpentry, and furniture making.

Attribution from: James E. Eckenwalder; Conifers of the World: The Complete Reference; ©2009

Tsuga diversifolia — accessioned in 1954 at the Morris Arboretum, Philadelphia, Pennsylvania; photo from 2020.
Photo by Katherine Wagner-Reiss
Tsuga diversifolia — a closeup of foliage detail.
Photo by Katherine Wagner-Reiss
Tsuga diversifolia — a closeup of foliage with a mature seed cone.
Photo by Katherine Wagner-Reiss
Tsuga diversifolia The Harper Collection of Dwarf & Rare Conifers located at Hidden Lake Gardens in Tipton, MI. Photo taken August of 2005. The leader on this specimen seems to be missing making it not the best of examples for this species.
Photo by Dax Herbst
Tsuga diversifolia
Photo by Crusier
Natural forest of Tsuga diversifolia in Fukushima
Photo by Forestry and Forest Products Research Institute, Japan
Tsuga diversifolia - foliage detail
Photo by Sigma64
Tsuga diversifolia - foliage detail
Photo by Wikipedia
Tsuga diversifolia - branch detail with ripening seed cones
Photo by Arboretum Mustila, Finland

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