Alnus cordata (Loisel.) Duby

Italian Alder is a distinctive species that quickly grows into a large, handsome, upright-conical tree. It has rather small, glossy, thick leaves, with typically cordate leaf bases and semicraspedodromous venation, and has large ovoid cones. It is most closely related to Caucasian Alder (Alnus subcordata) and relatives, and is separated by its smaller leaves, typically with cordate bases and shorter male catkins which appear in spring rather than over winter. Alnus japonica is also superficially similar but is distinct in having small ovoid buds, leaves with bases that are cuneate to truncate (never cordate), conduplicate in bud, and with much shorter male catkins. A. japonica is probably only distantly related despite Murai (1964) placing Italian Alder in Section Japonicae. This Section is likely to be a mixture of taxa which cannot straightforwardly be placed anywhere else. Italian Alder hybridises with A. glutinosa where the two grow together in the wild (Villani et al. 2021), giving rise to A. × elliptica.

Italian Alder is an exceedingly useful species – this is reflected in its wide availability in the nursery trade both for horticulture and forestry. It is drought tolerant, grows well in infertile soils, and is wind-firm, making it a useful species for urban forestry, wind breaks, soil improvement, agroforestry or land reclamation (Hirons & Sjöman 2019; CABI 2018). It should be widely grown, especially in urban areas, away from water containing Phytophthora alni. It is fast growing with a straight single trunk, with timber that stains red in sunlight. The timber is highly versatile and is used in a variety of ways, including for turning, carpentry, furniture, panelling, plywood and paper. The timber degrades rapidly when exposed to air or soil, but is more durable when immersed in water (Caudullo & Mauri 2016). It will freely self-seed in cultivation in full sun and is somewhat invasive in drier regions. The species appears to be somewhat resistant to Alder Leaf Beetle due to its thick leathery leaves (T. Baxter pers. obs.).

In horticulture this is a very ornamental species, and potentially a large tree. Bean called it ‘undoubtedly one of the handsomest of the alders’ (Bean 1976). Cultivated as an ornamental since the early 19th century, its many virtues include its ease of growth, large upright habit, and good foliage; it is also attractive in flower in early spring, but less so than A. subcordata which has much longer catkins. It is commonly planted as an amenity tree throughout suitable parts of Europe and North America, where it was in commerce by the 1850s (Jacobson 1996). There are many fine specimens in cultivation; the tallest on record was 31.5 m tall in 2016, growing at Stourhead, Wiltshire, UK. The tree with the largest recorded girth is at Sittingbourne Parish Church (Kent, UK; 3.46 m in 1999) (Tree Register 2021) which is larger than even the largest wild tree recorded by the website monumentaltrees.com (25 m × 3.32 m girth in 2020, at Piano Migliato in the municipality of Avellino, Campania, Italy) (monumentaltrees.com).