Download Article 143 Updated List Acer negundo_Box Elder

Weeds in our Area (Part One Hundred and Forty Three)
By Bob and Ena McIntyre – Garden Route Region.
UPDATED LIST: Acer negundo (Ash-leaved maple, Box elder)
A.negundo is native to North America and is well-known across the world. Today it is found in
China and in Australia. In Australia it has been declared an invasive alien species. Bearing in mind
our own experience with the invasive trends of Australian species in the RSA and vice versa, as
well the climatic similarities, it is easy to understand why the species has been moved from the Xlist as proposed category 3 to the updated list. The variegated hybrids have been particularly
popular because of their striking appearance - A.negundo variegatum is particularly attractive with
wide white or yellow-green leaf margins. In this sense A.negundo were regarded ideal subjects for
isolated “lawn” specimens or as a backdrop to shrubbery. The fact that they do well everywhere
except for the very dry regions of the country contributed to their popularity with landscapers and
home gardeners.
Description: The Box elder is a hardy deciduous species
that grows up to 10m tall. Quite different to other Acer sp.
which mostly have simple palm-shaped leaves; A.negundo
has compound pinnate leaves that usually have three to
seven leaflets. Simple leaves are occasionally present. The
leaflets are lance-shaped with serrated margins. The trees
often have several trunks and can form impenetrable
thickets. The bark on the trunks is pale gray or light brown,
scaly, deeply split into broad ridges. Leaflets are ±5-10 cm
in length and ±3-7 cm wide and translucent pale green in
colour. The flowers are small and appear in early spring on
drooping racemes 10-20 cm long. The seeds are paired samaras, each seed slender, 1-2 cm long,
with a 2-3 cm inward curved wing; they drop in autumn or may persist through winter. Seeds are
usually both prolific and fertile. Unlike most other maples, A. negundo bears male and female
flowers on separate plants, therefore both "male" and "female" trees are needed for either to
reproduce.
Invasive Status: Human influence has greatly favoured this species and it can be found in hedges,
gardens and vacant areas. The Box elder often grows on flood plains and other disturbed areas
with ample water supply, such as along riverbanks. The seeds are wind-dispersed and are also
eaten by birds. The updated list reflects A.negundo as Category 3 (regulated by activity). The
species may not be propagated or traded. In its country of origin its natural enemy is the Maple
Bug (also called the Box Elder bug) which will lay its eggs on all maples but shows a preference for
A.negundo.
Control: Remain alert to any seedlings appearing in your garden – remove and destroy.
References: ALIEN WEEDS AND INVASIVE PLANTS: Lesley Henderson - Copyright @ 2001
Agricultural Research Council. www.wikipedia.org. A-Z of Gardening in SA: W G Sheat