Ptelea trifoliata Aurea - Hoptree

Ptelea trifoliata, also known as Samaritan Elm, is a little-known North American species that is not widely planted in European gardens, despite its remarkable adaptability. This shrub or small tree is not an elm, but belongs to the same family as citrus trees, which explains why its foliage is also fragrant. Its golden colour in spring and autumn further enhances its appeal. Its discreet spring flowering is both fragrant and melliferous, giving way to decorative clusters of winged fruits that last until late in the season. Its trifoliate leaves give it an exotic look, especially since its rarity makes it difficult to identify. Hardy and very accommodating, it deserves to be more widely planted in our gardens.

Ptelea trifoliata is a member of the Rutaceae family, which includes about 160 genera, including the large group of citrus trees and related species, as well as numerous ornamental genera such as Choysia (Mexican Orange), Skimmia, and Boronia. Ptelea is monospecific and is native to a vast area covering eastern North America, from Mexico to the United States and Quebec. In the wild, it is often found anchored in rocky hillsides in mountainous areas, on shallow soils where it develops thick roots. The Hop Tree often develops several thin and twisted trunks, showing an overall open habit and a sparse and wide crown supported by upright and intertwined branches. It is a large shrub or small tree that is very hardy, with slow growth, reaching about 6 m (20ft) in height and 4 m (13ft) in width.

The cultivar 'Aurea' is a horticultural introduction that enhances the ornamental interest of this species. Even rarer than the type, it offers particularly decorative foliage in spring when the three-leaved compound leaves emerge with a beautiful yellow colour. They then turn lime green during the season before becoming golden again in autumn for a grand finale. The bark covering the trunk and branches is initially smooth and reddish-brown, but becomes more grayish and slightly grooved with time. The branches bear a very dense, deciduous foliage that falls late in autumn and develops late in spring. When crushed, it releases a musky and lemon scent, aromatic compounds that betray its membership to the Rutaceae family. The leaves, which are somewhat soft in texture and measure 6 to 15 cm (2 to 6in) in length, are divided into 3 ovate lobes with pointed tips.
Ptelea trifoliata 'Aurea' has a discreet flowering period in June, with clusters of small white-cream star-shaped flowers, 1 to 2 cm (1in) wide, appearing among the leaves. Intensely nectar-rich, they emit a heady fragrance reminiscent of honeysuckle, more noticeable at dusk, and more or less appreciated by humans, but attracting bees and butterflies. The flowers are followed in late summer by generous clusters of small nuts, each surrounded by a green, then yellow-brown oval membrane, measuring 2 to 2.5 cm (1in) in diameter and having a papyraceous texture. Dispersed by the wind, they are appreciated by many birds and small mammals. These fruits, also aromatic, can be used as a substitute for hops in beer production.
Very accommodating, this slow-growing small tree adapts to most soils, except for excessively acidic ones. It appreciates humus but can grow in poor soil, from moderately moist to moderately dry, and can tolerate drought once well-rooted. It also tolerates wind quite well. Hardy to about -20 °C (1°F), its adaptability and moderate size make it suitable for almost any garden. It can tolerate full sun, which is not always the case for golden-leaved plants that tend to scorch in this type of exposure, but it also grows well in partial shade.

If the green Hop Tree is suitable for wild, natural gardens, this golden variety is worthy of being included among other horticultural selections. You can create strong colour contrasts by planting purple foliage next to it, a classic but always effective combination. Choose the very attractive Cercis canadensis Forest Pansy, a small tree with heart-shaped leaves that are highly decorative. If you prefer lighter foliage, opt for the Albizia 'Summer Chocolate', where it's hard to decide what to admire most, between its fern-like cut leaves with an incredible almost black colour or its large feathery flowers. If you plant your 'Aurea' Hop Tree in the background, many smaller-sized shrubs also offer interesting purple foliage, such as the upright Sambucus nigra Black Tower, or for more compact forms, one of the many purple-leaved Physocarpus, such as 'All Black', aptly named, or the tiny Cotinus coggygria Lilla, a miniature version of the Smokebush.