T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Robinia pseudoacacia (False Acacia)

Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Rosids
Order: Fabales
Family: Fabaceae
Subfamily: Faboideae
Tribe: Robinieae
Genus: Robinia
Species: R. pseudoacacia
Binomial name: Robinia pseudoacacia
Synonym: Robinia pseudoacacia var. rectissima
Common name: False Acacia, Black locust

Robinia pseudoacacia is a rapidly growing, medium-sized, deciduous tree that is native to North America. It has been widely planted and naturalised elsewhere in temperate countries around the world. It is considered an invasive species in New Zealand as it forms dense thickets that shade out native plants. Its fragrant flowers complete with native flowers for pollinating bees. It is common throughout the North Island, in the South Island is found in Otago, Canterbury, Westland and Nelson. It inhabits forest margins, roadsides and waste places.

Robinia pseudoacacia is a tree that grows up to 25 m high. It has a rounded crown and a trunk up to 1 m in diameter. Young saplings have smooth, green bark while the bark of an older tree is a grey-brown colour and it is deeply furrowed. The young shoots and young branches are usually armed with two 1 cm long spines at the base of each leaf stalk. They are formed from pairs of stipules, leaf-like structures on the base of the leaf that become woody and sharp with age.
The leaves (20-30 cm) are pinnate (divided into a central axis bearing leaflets) with 3–11 pairs of oval leaflets and one extra terminal leaflet. The leaflets are a dark green above and are pale underneath. At maturity, the leaflets are almost hairless.
Flowering occurs from November to January. The flowers are pea-shaped and are in arranged in loose drooping racemes which are typically 10–20 cm long. The flowers themselves are cream-white with a pale yellow blotch in the centre. They are about 2.5 cm wide and are very fragrant.
The flowers are followed by shiny, smooth, hairless, narrow, flat seed pods (5-10cm long) whose upper suture (margin) is slightly winged. Each pod contains 4 to 10 seeds.

Robinia pseudoacacia reproduce by root suckering and by seeds. 
Root suckering is an asexual form of reproduction and is an important method of local reproduction for this tree. The trees vigorous root suckering forms groves of trees some distance from the main trunk. They are all interconnected by a common root system.

Robinia pseudoacacia is toxic and the poisoning of humans and livestock are occasionally reported. The leaves, young shoots, pods, seeds and the bark contain toxic components. Poisoning is due to the toxic protein toxalbumin robin and the alkaloid robinine. These toxins affect the gastrointestinal tract as well as the nervous system. Humans may display depression, weakness, dilated pupils, vomiting, bloody diarrhoea, weak pulse, the coldness of arms and legs, paleness, and shock.
Horses are particularly at risk, but all animals ingesting the plant may be poisoned. Horses that consume the plant show signs of anorexia, depression, incontinence, colic, weakness, and cardiac arrhythmia. Symptoms usually occur about 1 hour following consumption, and immediate veterinary attention is required.

Flowering November to January

The drooping racemes 

The flower with a pale yellow blotch in the centre. 

A dried open seed pod.

Young leaflets.

Two 1 cm long spines at the base of each leaf stalk.

Thanks to Wikipedia for text and Information:  http://creativecommons.org/licenses/by-sa/3.0/