The species are grouped according to a phytogeographic or ecological criterion in order to evoke different natural growth environments and to observe the various adaptations that plants have gone through over time.
Climate change has altered the geographical distribution of many plant species, favouring, for example, the spread of Mediterranean plants to continental Europe, including the Po Valley. The Garden, characterized by a local microclimate due to its location in the city centre, is able to house some typical species of the Mediterranean maquis, such as the holm oak (Quercus ilex), the Mediterranean tree par excellence, the lentisk (Pistacia lentiscus) and the immortelle (Helichrysum italicum) which gives out an intense aroma and the strawberry tree (Arbutus unedo) which blooms from October to March, in the same period when the previous year’s fruits are ripening.
Xerophytes plants are able to live in arid environments thanks to morphological or physiological adaptations that limit water loss by evaporation through the tissues. Some species are cultivated in one of the Garden’s flowerbeds, to represent the different survival strategies: for example, you will see leaves densely covered by fine hairs, reflecting sunlight and trapping dew drops as in Glaucium flavum, the growth of longer roots in order to absorb water from deeper under the soil as in Stipa tenuissima, or the sponge structure of stems and leaves of the so-called succulent plants (e.g. genus Sedum) due to cells that are capable of retaining moisture.
Hygrophytes are plants that have colonized humid environments by adopting strategies that favour the dispersion of water from their tissues: leaves with very thin, hairless epidermis; numerous stomata, tiny pores on the leaf surface; reduced root system and elongated stems. In the Garden you can find quite common specimens from around the world such as Alisma plantago-aquatica, the aromatic calamus (Acorus calamus) and the marsh hibiscus (Hibiscus palustris), but also species that are part of Lombardy’s protected flora, such as the siberian iris (Iris sibirica), the dwarf cattail (Typha minima) or the mouse garlic (Allium angulosum).
Some species bloom at the end of winter, early spring: these are the so-called undergrowth plants, such as lily of the valley (Convallaria majalis), winter aconite (Eranthis hyemalis) or cyclamen (Cyclamen sp.) which make the flower beds and the Arboretum of the Garden delightfully colourful, in the shadiest areas. In the course of evolution they have developed strategies to survive in an ecological space available for only a very short period each year, avoiding to compete with other species. In this brief timespan they are able to complete their lifecycle by defending themselves effectively, due to the toxic substances they produce, from herbivores hungry after the winter’s meagre diet.