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Plant of the month October

Common Name: Ombu, Bella Sombra

Scientific Name: Phytolacca dioica L.

Family: Phytolaccaceae

 

Etymology

Genus:  

Phyto - plant, lacca - dye. Refers to red dye produced by some species in the genus.

Species:

dioica - indicates individual plants are either male or female (dioecious)

Distribution

Native to the Pampa (Pampas) region of South America. Occurs in Argentia, Uruguay and the southernmost state of Brazil, Rio Grande do Sul.

Native Habitat

Grows in open grasslands or prairies. The climate is temperate and rainfall regionally variable from 500 mm to 1200 mm. Ombu trees are found in the lower rainfall areas.

Description 

A massive tree with a broad umbrella-like canopy. Trees can reach 12 to 18 metres in height, with a spread often equal to or greater than their height. Although listed as evergreen by most sources, our two trees are deciduous, losing their leaves each year in late winter. The massive swollen trunk and branches are the result of an abnormal thickening of the stem and not true wood. This reflects the Ombu’s evolution from herbaceous relatives. It results in fast growth but soft and spongy wood. You will often find fallen branches on the ground, pick one up and feel how light they are.

Flowers and Fruit

Plants are either male or female. Flowers are creamy white and occur in pendulous racemes. Male flowers have 20 -30 prominent stamens. Female flowers have a greenish tinge, are larger and feature a showy ovary.

Location in Garden

Middle Garden. Large, male plant near entrance to Succulent Garden. Younger plant in the Succulent Garden.

Information

Ombu trees are one of the only tree-like plants that live on the Pampas, a landscape dominated by grasses. They provide shade for gauchos (South American cowboys), other travellers and cattle in these landscapes. Their poisonous sap makes them resistant to cattle grazing, locust and other pests. Leaves are sometimes used as a laxative or purgative.

The Ombu’s massive spongy trunk contains water storage tissue, providing protection against intense grass fires that occur in its native habitat.

The larger of our two trees was planted in 1955 by Allan Correy. Allan joined these gardens as a horticultural apprentice in 1946. He studied horticulture and his leaving certificate at night before gaining a position as a botanical assistant. He later studied landscape architecture in England and the USA before returning to Australia. He designed Mount Lofty Botanic Garden in South Australia before becoming the NSW government landscape architect. In the 1970s he started the undergraduate program in landscape architecture at the University of Sydney. In 1993, he returned to the Royal Botanic Garden Sydney as a volunteer guide, leading our free guided tours until he retired in 2012. Allan passed away in 2016 and this wonderful tree is a great reminder of his accomplishments and contribution to horticulture in Australia.

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