A very common invasive species at Chadwick lakes is the Castor Oil tree, indigenous to Africa, a fast-growing perennial flowering 4 m shrub which can grow to a small 12 m. tree.
Easily identified by its glossy dark green 15 – 45 cm. leaves growing on long stalks, which resemble a palm of the hand with 5 – 12 deep lobed fingers. Young leaves may be dark reddish purple, changing as they mature.
The tree matures in the first season. The petal-less flowers, can almost be seen all the year round. These can be either male or female, borne on the same tree. Female flowers having prominent red stigmas are fewer than males. Male flowers are yellowish-green with visible creamy pollen bearing sacks. Flowers can be pollinated by wind or by insects, but they can pollinate other flowers on the same tree.
The 10 – 20 mm spiny reddish-purple fruit is quite showy. These contain large, oval shiny bean-like 9 – 17 mm seed, reddish-brown to blackish, with shades of white, grey or brown markings.
The seeds can be dispersed in a number of ways: by birds, rodents, adhering to muddy boots or clinging to vehicles and machinery, and also by flood waters. Besides when the capsule dries, it splits and ejects the seeds and throws the seeds possibly to more than 5 m. away from the tree.
The presence of ricin – a poisonous protein – found in the seeds, is a water-soluble toxin, present also throughout the plant. Seeds are poisonous if chewed and ingested.
The abundant wind borne pollen produced by the tree can easily be inhaled, possibly causing allergic reactions and asthma.
The castor oil is legally declared as an invasive, alien or environmentally incompatible species in the Maltese Islands.