A collector’s item

The Botanical Garden is home to a variety of species of trees that are as diverse as they are rare. The centrepiece of this collection quietly grows in the lower part of the garden, at a bend in the path, a conifer with a somewhat unusual silhouette: this is a metasequoia or dawn redwood. It is thought to be one of the very first specimens of its kind ever planted in Brussels, perhaps even in Belgium.

Just a youngster for a ‘living fossil’

Like the ginkgo and the magnolia, the Metasequoia glyptostroboides was known through fossil traces. Its leaves have been imprinted in rock over the course of evolutionary history. Thanks to this fossil record, it was understood that the metasequoia was already flourishing on our planet during the Cretaceous period, some 70 million years ago. Its needles would have been nibbled by the great plant-eating dinosaurs. In the presence of the specimen that grows in the Botanical Garden, you experience time on a different scale.

How could a tree of this species have found its way here? In 1941, the metasequoia was discovered growing in the wild in south-west China. The news caused a sensation among botanists and horticulturalists and in the late 1940s, seeds and seedlings were sent to many botanical gardens in Europe. This specimen was planted in 1949, making it a little under 70 years old. A mere youngster for a tree considered to be a ‘living fossil’.

In its young lifetime, the metasequoia at the Botanical Garden has witnessed quite some changes in its surroundings. It has seen the garden converted into a public park in 1958, and then watched its gradual decline as a result of urbanisation and vandalism. Little by little, the area left uncultivated around it has been gobbled up and partitioned to make way for traffic: the ancient ring of fortifications around Brussels has become the ‘Petite ceinture’ (the inner ring), the boulevards have been widened and new streets have been created. The subsoil and water tables have been disrupted to construct the metro line and sink the foundations for the tall buildings that surround the garden.

If the metasequoia has survived this degradation, like many remarkable trees and shrubs, it is thanks to the loving care provided by the Region’s public greenskeepers. Since 1991, they have been fighting to restore the garden’s ecosystem, a long-term undertaking that continues today. This is why walkers can still enjoy the metasequoia at the heart of this urban arboretum.

A collector's specimen

In the 1970s, the metasequoia began to die off in China. Chinese peasants were using their tender foliage for livestock feed. In Europe, the metasequoia became quite common in parks. They also started to be planted along avenues: they are much appreciated for the distinctive beauty of their foliage and their slender profile.

Ordinarily, this tree is a fast-growing conifer. Its architecture is made up of a distinctly pyramid shaped crown with branches rising upwards from a straight, cylindrical trunk. This can be seen in the very fine specimens located on the Avenue de la Brabançonne, as well as in the Leopold Park near the pond. However, the specimen in the Botanical Garden has a different type of trunk, particularly at its base. It is completely deformed*: its gnarled shape is convoluted and its base is extremely wide for such a young tree. This botanical curiosity, combined with the rarity of the species and the exceptional circumference of its trunk, make it a notable tree that is included in the scientific inventory of the Region.

The name metasequoia contains sequoia: these two trees belong to the same family. The bark is similar. It is reddish brown and highly fibrous, but in the metasequoia (dawn redwood), it does not form as thick layers as in the sequoia (coast redwood). Also, it is a small tree, growing only some 15 metres tall, much less impressive than its giant cousin.

While their branches have a similar shape, the metasequoia can be distinguished by its foliage. It has the specific quality of turning ochre and then red in autumn, and it loses its needles in the winter. This phenomenon, which also occurs in the larch and the bald cypress, is rare in conifers. The needles, which emerge tender and green in the spring, are flat, tender and supple, almost feathery-soft. They are arranged symmetrically, directly across from one another on each side of the stem. When summers are too hot, they may fall off prematurely. But if enough rain comes before autumn, the needles will regrow.

A time capsule in the evolution of plant sexuality

If you happen to pass the metasequoia in the early spring, you may get to see or touch its flowers on the branches directly overhanging the path. They bloom before the foliage emerges and are very discreet. The male flowers resemble bunches of grapes that hang from the tips of the branches. They produce the pollen. The female flowers are tiny green dome-shaped pellets scattered here and there on the branches.

You could hardly call them ‘flowers’ as they do not have petals, nor ovaries or stigmas: the parts that make up most modern flowers. In these primitive flowers, there are only semi-open scales. This is the defining characteristic of the entire group of gymnosperms: they have a structure that offers rudimentary protection for the future seed, but is not yet perfected as a flower.

Thus, if you look very carefully, you can already see the shape of the fruit: a miniature cone measuring 1 to 2 mm. Its scales, shaped like tiny shields or little shovels (this shape is called peltate) are open in order to be able to receive the pollen, which will be transported by the wind. Once the pollen settles there, the fruit closes and the seed will be able to form. The fruit will then grow. Or rather, a cone, which is not really a fruit: the seed is not embedded in a large fleshy fruit like the seed of an apple, for example.

The cones of the metasequoia resemble those of the sequoia: when mature, their shape is rounded, but they are much smaller (1 to 2 cm), and the light shines through the gaps between their scales when they have spread open. The seeds released from them are unlikely to germinate in Belgium. Currently, metasequoias are propagated from cuttings in nurseries.

Although they do not exceed 20 m at our latitudes, they may reach 30 to 50 m in height in their original habitat. They tolerate pollution well. This collector's specimen, already rare for its age, should therefore be around for a long time to come.

(Story and photos created by Priscille Cazin https://www.sylvolutions.eu)