Aesculus hippocastanum Monstrosa

Aesculus hippocastanum 'Monstrosa' is a Horse Chestnut tree that is also known as Monstrous, because it has a mutation called fasciation, which is quite common in the plant world. This mutation is responsible for its small size and the very unusual appearance of its branches. More picturesque than ornamental, it will delight enthusiasts of botanical curiosities. Its foliage resembles that of the classic horse chestnut, but smaller, and it grows on branches that are shaped like atrophied crests, carried by remarkably stout, curiously flattened, furrowed and twisted branches. This dwarf tree astonishes with its supernatural structure, especially interesting to observe in winter when it is devoid of leaves.

Aesculus hippocastanum 'Monstrosa' belongs to the Sapindaceae family, formerly known as the Hippocastanaceae family. The type species, contrary to what its common name of Horse Chestnut suggests, is native to Macedonia, a region that includes northern Greece, Albania, and southern Bulgaria. It is a forest species. In nature, the common horse chestnut can reach a height of 25m (82ft) with a spread of 15 to 20m (49ft 2in to 65ft 7in).

The Monstrous horse chestnut is a grafted variety. Its trunk and branches are covered with a brown to reddish bark, initially smooth, becoming grey and fissured with age. Its habit is variable depending on the subjects, but generally quite narrow and upright. A 15-year-old specimen will not exceed 1.50m (4ft 11in) in height. Eventually, after many years, the tree reaches a height of about 3m (9ft 10in). The crown is irregular, very dense. The deciduous foliage appears in spring and falls in autumn. In winter, large reddish buds covered with shiny resin can be seen on the branches. The foliage is composed of leaves measuring less than 10cm (3.9in) long, divided into 5 to 7 dentate leaflets, light green in colour, strongly veined and wrinkled. Flowering occurs in May-June, on branches that are already leafy. It takes the form of upright pyramidal clusters called thyrses, 20cm (7.9in) long, composed of numerous small flowers, 1cm (0.4in) wide, which are close to white in colour. Fasciation and cresting, of uncertain origin, are the result of abnormal growth at the apex of a stem. Fasciation is characterized by flattened, striated stems in the form of a bundle, while cresting gives them a crest-like appearance.

The Monstrous Horse Chestnut stands out well, as an isolated specimen or in an exotic-inspired bed, with ferns for example. It can also be adopted in a large pot on the terrace. Very hardy, it adapts to any deep soil that remains slightly moist, even limestone. Collectors of unusual plants will also appreciate other twisted trees: Corylus avellana ‘Contorta’ and its purple version Corylus avellana ‘Red Majestic’, the willow Salix erythroflexuosa, Robinia pseudoacacia ‘Twisty Baby’, or Poncirus trifoliata 'Flying Dragon', a very strange hardy citrus.