Daisy tree  (Scalesia stewartii)

Classified as Vulnerable (VU) on the IUCN Red List (1).

Having descended from a single daisy-like ancestor that colonised the Galapagos many millennia ago, the genus Scalesia is now one of the most significant plant groups in the archipelago (3) (4). Rivalling Darwin’s more famous finches for levels of diversity and endemism, Scalesia comprises 15 species of tree and shrub commonly known as daisy trees (3). Scalesia stewartii is a small tree or shrub that grows up to 3 metres tall and has alternate leaves with long, white hairs on the lower surface. The daisy-like flower-heads are made up of 35 to 90 white flowers (2).

Scalesia stewartii is endemic to the Galapagos Islands, where it is restricted to the east of Santiago Island, and the neighbouring islet of Bartolomé (1) (2).

Found in sparsely vegetated arid lowlands (1) (2).

Very little is known about the biology of Scalesia stewartii, but, in common with other species in the genus, it has dandelion-like seeds dispersed by the wind (5).

Since humans arrived on the Galapagos, dramatic ecological changes have been caused by agricultural activities, exploitation of native species, and the introduction of non-native animals and plants (4). Consequently, many species of Scalesia are now under significant threat of extinction (3) (4). A study conducted in 2002 revealed that introduced goats and scale insects were having a serious effect on Scalesia stewartii (4). Although goats have now been eradicated from Santiago (6) and the scale insect has been brought under control by the introduction of a biological control agent (7), Scalesia stewartii is still regarded as Vulnerable given its highly restricted distribution (8).

Scientists at the Charles Darwin Research Station are involved in several projects to restore and preserve populations of Scalesia species, including those on Santiago Island (3). A project that began in 1997 culminated in the eradication of all goats, pigs and donkeys on Santiago Island by 2005 (3) (9). Since the removal of the goat population on Santiago Island, the native vegetation has made a remarkable recovery. Further restoration efforts are now underway that will help to re-establish natural ecological conditions on the island (9).

For further information on the conservation of endemic flora and fauna of the Galapagos see:

• The Charles Darwin Foundation:
  www.darwinfoundation.org