The trees and shrubs are planted according to family groups. The arrangement corresponds to the basic concept of Armen Takhtajan, one of the most important systematists of the 20th century. The best time to explore the arboretum is the months of April / May, when most of the trees are flowering, and September / October, when the trees show their splendid autumn colors.
1. Ginkgo and conifers
The group of the gymnosperms is divided into different areas. Ginkgo, swamp cypress, yew and a part of the pine trees (fir, spruce, larch and cedar) were housed in a rather shaded and partly moist area. The pines (genus Pinus) are on the opposite side on a sunny south slope.
2. Witch hazels and catkin-bearing plants
This group of woody plants are species which are considered to be relatively original. Most representatives have kitten-shaped inflorescences and are wind-flowered. This group includes a large proportion of our lawns of the temperate zone, e.g. elms, oaks, beeches, birches, alders, hornbeaks and plane trees. This group also contains the witch hazels, which unfold their flowers at mild temperatures in the middle of winter.
3. Magnolia and pinna trees
Among the magnolia trees are stately trees (tulip tree) as well as some of the most beautiful flowering plants, such as the well-known tulip and star magnolia. The spice bushes belong to this group of relatives. A further large group in this section are the pinna trees, whose main focus lies in the tropics. These include, for example, the soaps, such as, for example, wig, cork, pimples and vinegar. The latter group includes the many magical maples with an extraordinary variety of leaf and bark structures as well as the horse chestnut trees.
4. Willows, poplars and lilacs
The group of willow species, with their simple flowers, is very isolated in the plant kingdom and is associated with various related groups. In the northern temperate zone, two genera are common: willow trees (Salix) and poplars (populus). Of the pastures, about 450 different species are known, while the poplars are about 50 species. In addition, there are several other related groups, such as the gentian ones, including ash, lilac, forsythia, honeysuckle, elderberry and snowball.
5. Rose family and leguminous
The rose plants, with their approximately 100 genera and about 3,000 species, form a very important family, which includes the majority of our native fruit trees as well as many magnificent flowering plants, eg ornamental apples and Japanese flower cherries as well as rock pears, white thorns and mountain ash. This area is particularly beautiful in May when the fruit trees and ornamental cherries unfold their flowers in many different forms and colors. In this section can be found also the 'Rosarium' with about 200 different types of roses and varieties.
In addition to the rose plants, this area of ??the arboretum is also associated with legume fruits (legumes).
6. Limes, cornels and spindle trees
To the linden family belong in total about 50 genera, whose main spread lies in the tropics. Only the genus Tilia (lime) about 45 species is spread in the northern hemisphere.
In addition to the lime trees, there are two other groups of relatives: the spindle tree plants and the cornels. Of the latter we know above all the common cornelian corn (Cornus mas). In this genus, however, there are still many magnificent ornamental shrubs with large, colored high-leaves and a conspicuously stagiform growth. To the spindle-tree plants, on the other hand, belongs the native European spindle (Euonymus europaeus). With over 200 species, this species has produced numerous ornamental shrubs with colorful autumn colors and strikingly colored fruits, which are often planted in the gardens because of their small size.
source: [DE] Arboretum Ulm