The largest section of the garden, at the back of the Biology Department buildings, extends to the bastions of the city; is mostly dedicated to distinct collections of particular value (e.g. the carnivorous plants) and to the reconstruction of natural habitats. The Back arden includes: the grove of broad leaved trees; the greenhouses; an area of medicinal herbs, once known as ‘simples’, or, more precisely, “simple principles” (in which the drugs were directly extracted from the plants) and from which derives the denomination ‘Garden of the Simples’ – ‘Giardino dei Semplici’; two artificial ponds with aquatic plants, and; a woodland consisting largely of broad leaved species of temperate climates. In the latter zone, there are also several monumental tree specimens, in particular an old Sweet Gum (Liquidambar styraciflua), a Taxodium distichum, a Pistacia atlantica, and several majestic poplars.
The grove of Broadleaved Trees
A small, raised area with several woody plants. Some of the plants – many recently introduced – come from the forests in the hills surrounding Bologna (both the Gessi bolognesi and the Apennines around Bologna). Herbaceous plants have been introduced, in conformance with the themes of the woody vegetation. The main elements marking the structure of the grove are: the Hop Hornbeam (Ostrya carabinieri Scop.), with a scaly, rough bark, and alternate and double-toothed leaves 3–10cm long. The distinct fruit clusters of nutlets hang almost 5cm long, which give the tree its common name; the Manna Ash (Fraxinus aunts L.), with flowers in dense panicles produced before the new leaves appear in late spring; the Black Elder (Sambucus nigra L.); the true service tree and the wild service tree (Sorbus domesticate L. and Sorbus terminates (L.) Crantz, respectively); the black alder (Alnus glutinosity L.), a medium size tree that thrives in wet locations.
In springtime, the underbrush is characterised by the beautiful and exuberant blossoms of herbaceous plants with like lungwort (Pulmonaria vallarsae Kerner), periwinkle (Vinca minor L.), hellebore (Helleborus viridis L.) and the Italian arum (Arum italicum Miller). This stemless, toxic species native to Europe has an erect, finger-like spadix covered with minute, creamy white flowers. The spadix is partially enveloped by a large, sheath-like, light green spathe. In summer, the plant develops attractive, bright orange-red berries.
Amongst the shrubs, the most noteworthy are: the guelder rose (Viburnum opulus L.); the firethorn (Pyracantha coccinea Roemer), with typical, small, orange/red berries; the evergreen butcher’s broom (Ruscus aculeatus L.); the common juniper (Juniperus communis L.).
Aquatic plants require special morphological, physiological and anatomical adaptations for living in aquatic environments. Aquatic vascular plants have originated on multiple occasions in different plant families: Despite evolving independently, they acquired similar growth habits (convergent evolution) because of living in a analogous environment, and so facing the same environmental factors.
In the two artificial ponds, aquatic plants are grouped according to their geographical origin:
– round pond with Europe-native plants, e.g. kingcup (Caltha palustris L.), European white waterlily (Nymphaea alba L), bog-bean (Menyanthes trifoliata L.), sweet flag (Acorus calamus L.).
– bean-shaped pond with exotic plants. This includes: the well-known papyrus sedge (Cyperus papyrus L.); the water hyacinth (Eichhornia crassipes (Mart.) Solms), with its broad, thick, glossy leaves floating above the water surface – since the roots of Eichhornia crassipes naturally absorb pollutants, the plant is cultivated for waste water treatment; Nelumbo nucifera Gaertner, commonly called sacred lotus in reference to the sacred and symbolic status the flower holds in Buddhism and Hinduism. Recent researches demonstrated that the lotus has the remarkable ability to regulate the temperature of its large, cupped, pink flowers.
Last but not least, Azolla caroliniana Willd., a small freshwater aquatic fern, native to the Americas, naturalized and growing as wild in Italy. This plant grows very fast on backwaters pervading rapidly the environment.