Freitag, 16. März 2012

Plant of the Day (March 16th, 2012) - Thuja occidentalis L.

A new day and a new conifer. This time, I want to present you Thuja occidentalis L. from the Cupressaceae family. In English, this tree is known as “Eastern Arborvitae” or “Northern Whitecedar”, while German names for this species are “Abendländicher Lebensbaum” (Occidental Arborvitae) or “Gewöhnliche Thuja”.

T. occidentalis - habitus

It's a tree, which can reach a height until 25 metres. Normally, it has a single, straight stem but grows also multi-stemmed. The habitus is conical with a dense foliage from the bottom to top. The branches are very flat, as well as the yellow-green leaves, which are scale-like.

T. occidentalis - branches & leaves

They are covering the whole branch in a fan-shaped pattern and are arranged imbricated, so each leaf overlaps the neighbouring leaf a little bit. There are also glands at the base of each leaf; giving the foliage a aromatic apple-like smell. On the other hand, these essential oils (most of them are terpenes like Thujon) are toxic and may cause skin irritations and, after consumption, vomiting, gastrointestinal complaints and diarrhoea.

The bark of young trees is reddish and turning grey with ages. It's also very fibrous and fells of in long, thin strips.

T. occidentalis - female, ripe cones

As with the most Cupressaceae, T. occidentalis is monoicous with male and female coness. The male cones are reddish and elongated, while the female, ovoid cones, which you can also see on my pictures, are brown. Because a single tree is able to make a lot of female cones, trees can have a brownish look. Each female cone consists of two pairs of seed scales, which opens at ripening. So, open cones look a little bit like small, brown tulips. The seeds are winged.

Sometimes, T. occidentalis is confused with the similar looking Platycladus orientalis (L.) Franco (Chinese Arborvitae), which belonged to the Genus Thuja for a very long time. However, the cones of this species have a complete different look, the seed is not winged and the branches grows upright.

T. occidentalis - bark

As the name suggests, T. occidentalis is native to North America and can be found in the Area of the Great Lakes in Northwest USA and South Canada. It grows on basic and wet soils on lime and tolerates shading. So, it can be found e.g. in swamps, the shores of lakes, riversides, cliffs uplands and so on. In this regions, T. occidentalis is one of the main forest trees. Sometimes, the wood is used for fencing, posts and for log cabins.

Because of its Cypress-like apperance, T. occidentalis is also a popular ornamental tree for parks, gardens and hedges. So, today it can also be found all over the world. In this case, the plants are often cultivars; most of them dwarf forms, because they'll not become so high like the wild form, which is an advantage for gardeners.

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