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photo

Shoot of an ornamental specimen (Arcata, CA) showing foliage and a current-year cone [C.J. Earle].

photograph

Plants growing beneath Abies nephrolepis on the Shkotovo Plateau, Ussuriland, Russia [Vladimir Dinets].

 

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Conservation status

Microbiota decussata

Komarov 1923

Common names

Microbiota, or Russian arborvitae (Rose 2005). Ude people call it kurumkurinda, 'talus pillow' (Vladimir Dinets, e-mail, 1998.01.10).

Taxonomic notes

The sole species in Microbiota Komarov 1923, it was first recorded by botanist I.K. Shishkin in 1921, in the mountains northeast of Vladivostok (Rose 2005). Schiskin thought it a specimen of Juniperus pseudosabina, but Komarov saw more clearly, and determined that it is most closely related to Platycladus orientalis. The two species share wingless seeds and a decussate architecture of the female cone; the foliage is dimorphic but not in the same way as species of Juniperus (Farjon 2005). More recent molecular studies place the two genera in a clade sister to Tetraclinis (Gadek et al. 2000). Thus a substantial portion of Cupressaceae diversity is accounted by three monotypic genera distributed from Ethiopia to Siberia; a fine example of the relict nature of the Cupressaceae.

Farjon (2005) speculates that Microbiota evolved vicariantly from Platycladus, which has a similar distribution but occurs at lower altitudes and in more mild climates. The two taxa could have become reproductively isolated by Pleistocene climate changes, after which Microbiota became better adapted to its harsh mountain home.

Description

Monoecious evergreen shrub with low crown and decumbent habit, 25-50(-100) cm tall. Shoots flat, bark brown. Leaves on generative shoots are oval-shaped, 2 mm long, 2 mm wide; on vegetative shoots - oval, pointed, with eliptic gland on upper side (leaves in shadowed inner parts of crown lack glands). Some leaves can be needle-shaped. Cones dry, to 6 mm long, 3 mm wide, with scales 3 mm long. Each cone produces 1 seed. Seeds upright, rounded-oval, smooth, brown, wingless. Pollination April-May, seeds mature August-October (Harkevich and Kachura 1981, Rose 2005). It superficially resembles spreading species of Juniperus, but he drooping branch tips distinguish it as a very different conifer.

The plant bears cones rather rarely and sparsely, and in any case they are minute in size. Komarov could only find plants bearing seed cones and thus described it as dioecious; only in 1963 was it published as monoecious. The foliage turns a bronze color in winter, an adaptation that may improve photosynthesis in low light conditions (Farjon 2005).

Distribution and Ecology

Russia: Sikhote Alin Province, Primoriye, from near Vladivostok north to the Anyuy River. A map in Kharkevich (1985, cited by Bachman et al. 2007) shows dots distributed more or less contiguously between Vladivostok and the Anyuy River, suggesting a total occupied range with a circumscribed area of at least 70,000 km2. Although it is listed as rare in the Red Book of Russia, but its habitat is on the whole not threatened as it occurs in remote localities and in vegetation types that are not subject to changes in land use except for some forested localities nearer Vladivostok. There is no evidence of decline (Bachman et al. 2007).

It occurs at elevations of 30 to 1365 m on well-drained sites and is very cold-hardy, enduring temperatures of -40° (Bachman et al. 2007, Rose 2005); hardy to Zone 3 (cold hardiness limit between -39.9°C and -34.4°C) (Bannister and Neuner 2001). Found both within montane forest and in the alpine zone, and may cover substantial areas as a ground cover of more or less contiguous plants. Common forest overstory species include Abies nephrolepis, Picea jezoensis, Pinus koraiensis, Acer ukurunduense, Alnus maximoviczii, Betula ermanii, and Sorbus amurensis. In alpine areas or on talus it often grows with Juniperus sabina var. davurica, Pinus pumila, or Rhododendron mucronulatum (Farjon 2005).

"Some plants cover up to 4 sq. m, but they are only 20-50 cm high. It is well-adapted to fire. Lightning often provokes spectacular explosions of oil fumes on Microbiota-covered summits, but with no harm to the plants themselves" (Vladimir Dinets, e-mail, 1998.01.02).

Big tree

Not very! Specimens a meter tall are recorded as exceptional.

Oldest

No data.

Dendrochronology

No recorded use as of 2009.

Ethnobotany

I have found no record of its use by native peoples, and the species did not leave the Soviet Union and enter the horticultural trade until the late 1960s (Farjon 2005). In cool climates, it has become popular as a low-growing ornamental conifer (Rose 2005).

Observations

Remarks

The generic name refers to the diminutive size of the plant; the epithet decussata may refer to either the decussate foliage or the decussate arrangement of seed scales in the female cone.

Citations

Bachman, S., A. Farjon, M. Gardner, P. Thomas, D. Luscombe, and C. Reynolds. 2007. Microbiota decussata. In: 2008 IUCN Red List of Threatened Species. www.iucnredlist.org, accessed 2009.04.17.

Harkevich, S. and N. Kachura. 1981. Rare Plant Species of The Soviet Far East and Their Conservation. Nauka, Moscow (in Russian).

Kharkevich, S.S. 1985. Plantae Vasculariis Orientis Extremi Sovietici [Vascular Plants of the Soviet Union’s Far East]. Nauka, Leningrad.

Rose, Nancy. 2005. Microbiota decussata: A versatile conifer. Arnoldia 63(4):15-16.

See also

Farjon (2005) provides a detailed account, with illustrations.

Last Modified 2012-11-28